1. The importance of dietary lipids for carotenoid-based ornaments has rarely been investigated, although theory predicts that dietary lipids may control the development of these widespread animal signals. Dietary lipids have been suggested to enhance the expression of male carotenoid-based ornaments because they provide carotenoids with a hydrophobic domain that facilitates their absorption and transport. Dietary lipids may also enhance the uptake of tocopherols (vitamin E), which share common absorption and transport routes with carotenoids. Here, we test whether dietary lipids enhance carotenoid availability and male carotenoid-based colorations. We also explore the effects of dietary lipids on plasma tocopherol concentration, which allow disentangling between different pathways that may explain how dietary lipids affect ornamental expression.

2. Following a two-factorial design, we manipulated dietary access of naturally occurring fatty acids (oleic acid) and carotenoids (lutein and zeaxanthin) and measured its effects on the circulating concentrations of carotenoids (lutein and zeaxanthin) and vitamin E (α- and γ-(β-) tocopherols) and on the ventral, carotenoid-based coloration of male common lizards (Lacerta vivipara).

3. Lutein but not zeaxanthin plasma concentrations increased with carotenoid supplementation, which, however, did not affect coloration. Lipid intake negatively affected circulating concentrations of lutein and γ-(β-) tocopherol and led to significantly less orange colorations. The path analysis suggests that a relationship between the observed colour change and the change in plasma concentrations of γ-(β-) tocopherol may exist.

4. Our study shows for the first time that dietary lipids do not enhance but reduce the intensity of male carotenoid-based ornaments. Although dietary lipids affected plasma carotenoid concentration, its negative effect on coloration appeared to be linked to lower vitamin E plasma concentrations. These findings suggest that a conflict between dietary lipids and carotenoid and tocopherol uptake may arise if these nutrients are independently obtained from natural diets and that such conflict may reinforce signal honesty in carotenoid-based ornaments. They also suggest that, at least in the common lizard, sexual selection with respect to carotenoid-based coloration may select for males with low antioxidant capacity and thus for males of superior health.

1. Natural selection can generate correlated suites of phenotypic traits by acting independently on physiological and behavioural characters or on mechanisms that exert pleiotropic actions.

2. Current theory, supported by artificial selection studies, suggests that physiological and behavioural stress responses are at least partially under genetic control and covary in a predictable manner. Indeed, physiological mechanisms such as hormonal stress responsiveness may underlie variation in behaviour, including consistent behaviours described as temperament or personality, with bolder, more exploratory and active individuals being less hormonally responsive to stressors.

3. This relationship, however, has yet to be demonstrated in natural populations. We investigated the relationship between hormonal and behavioural stress responsiveness in multiple natural populations of a tropical freshwater poeciliid fish, Brachyrhaphis episcopi, that experience different levels of predation pressure and hence encounter different rates of stressful events. Predation can impose a strong selection pressure, and living with a high risk of predation is known to select for specific behavioural traits.

4. We quantified variation in stress responsiveness via cortisol release rates (exp. 1) and behaviour in an open field test followed by cortisol release rates (exp. 2). Populations exposed to high levels of predation were consistently more exploratory and active and had lower release rates of cortisol in response to a stressor than conspecifics sampled at sites with few predators.

5. However, this difference in stress responsiveness was only apparent after fish had experienced the mild stress of behaviour testing (in exp. 2), which resulted in elevation of cortisol levels. The relationship between hormone release and behaviour was also not apparent within populations once independent factors were controlled for, highlighting the importance of factors such as size and sex on individual variability.

6. This study demonstrates that the relationship between hormonal and behavioural stress responsiveness can result from natural selection pressures, such as that imposed by predation.

1. Experiments in ecology occur in the laboratory, mesocosm or field. The choice of venue can influence the outcome and may be associated with trade-offs involving realism and precision.

2. We evaluated these trade-offs in an experiment measuring effects of venue on larval traits of Rana temporaria tadpoles. The design included laboratory, mesocosm and field venues, crossed with two treatments (presence and absence of caged Anax imperator dragonfly larvae). Realism of venues was evaluated by comparing experimental with wild tadpoles.

3. Venue influenced nearly every trait we measured, but some were more sensitive to venue than others. Larval and metamorphic performance, external morphology and predator-induced plasticity in many traits varied among venues, while behaviour was less dependent on venue. Tadpoles in mesocosms were most similar to those in field enclosures and the wild, although the phenotypic response to predation risk was greatest in the mesocosm venue. The laboratory environment triggered highly distinctive morphology. Precision was not higher in the laboratory than in other venues.

4. This study suggests that both constraints and research questions must be considered when choosing an appropriate experimental venue.

1. Seasonal carry-over effects may be important structuring components of avian life-history cycles. However, little is known on physiological transitions between stages and on phenotypic compromises that may be made at such time to improve fitness.

2. We studied postmigratory body remodelling in red knots (Calidris canutus islandica) arriving on the Arctic breeding grounds. Our objectives were to determine the effects of body reconstruction and preparation for breeding on maintenance energy costs and to determine whether weather conditions can force compromises between functions required for postmigration recovery of body composition, thermoregulation and breeding.

3. During two consecutive springs at the northernmost land on Earth (Alert, Ellesmere Island, Canada, 82°30′N), we monitored changes in knots post-arrival body stores. Using ultrasonography, we also tracked changes in gizzard size, an indicator of gut size, and pectoral muscle thickness, not only an endogenous protein source but also a thermogenic organ. We measured basal metabolic rate (BMR) throughout reconstruction and compared it with BMR of nonbreeding red knots wintering in the Dutch Wadden Sea.

4. Arriving knots faced temperatures up to 13 °C lower than during midwinter. Birds arrived with large body stores and pectoral muscles, which declined in size while they grew their gizzard and prepared for breeding. BMR at arrival was indistinguishable from winter BMR and increased linearly throughout reconstruction. BMR increased up to 69% faster in females than males, likely due to the development of their reproductive organs.

5. Birds had lower body stores but larger muscles in the colder year, and muscle loss was correlated with the warming of spring temperatures. Therefore, muscles would not only serve as a nutrient source, but their thermogenic function could also provide the flexibility to cope with high thermostatic costs in the spring. However, retaining muscles for shivering may limit protein recirculation and delay the onset of breeding.

6. Postmigratory recovery therefore involves significant energy costs and arriving birds likely have to make physiological compromises, depending on spring conditions, which may impact on fitness. Although this period is clearly critical in the life cycle of red knots, it is one of the least understood life-history stages in Arctic-breeding shorebirds.

1. Adaptive phenotypic plasticity enables plant lineages to match trait expression to contemporary environmental conditions, while maternal environmental effects arise in response to environmental factors encountered in the previous generation. Maternal effects on seed dispersal distance in spatially structured habitats could determine the level of microenvironmental variation encountered by a lineage across generations.

2. We conducted a greenhouse experiment that spanned three generations to assess the relationship between variation in maternal phenotype and seed dispersal distance, maternal environmental effects on fitness in response to variation in nutrient availability across generations, fruit morphology, and seed dispersal distance in populations of an invasive annual forb Erodium cicutarium growing on serpentine and non-serpentine soils. Macro- and micronutrient availability is lower on serpentine soils than surrounding non-serpentine soils and result in a significant source of stress for plants growing on serpentine soils.

3. The combined effects of maternal and offspring environment on the fitness of E. cicutarium were substantial. We demonstrated a positive relationship between fruit length and ballistic dispersal distance, and found no evidence for a trade-off between fruit length and seed number in either high- or low-nutrient environments. The maternal environment had a significant effect on the mean ballistic seed dispersal distance such that lineages exposed to consistent nutrient availability across generations disperse their seeds significantly farther than lineages exposed to environmental heterogeneity. Although lineages exposed to different environments across generations on average dispersed their seeds shorter distances, there was a marginally non-significant trend for greater variance in dispersal distance in response to environmental heterogeneity than lineages exposed to consistent environments across generations. On average, lineages from non-serpentine source populations had significantly greater variance in dispersal distance than serpentine lineages.

4. This pattern of maternal effects on mean seed dispersal distance, and the observed trend for maternal effects on the breadth of the dispersal kernel, could be adaptive in the mosaic serpentine soil landscape where E. cicutarium was collected. However, field experiments are needed to rigorously demonstrate the fitness consequences of maternal environmental effects on seed dispersal.

1. Plants must balance water expenditure from their crown with water supplied through root and stem tissues. Although many different combinations of hydraulic traits could accomplish water balance, we ask whether variation across species in stem hydraulic traits has been concentrated along few, or many, dimensions of trait variation.

2. We measured stem hydraulic traits for 120 woody dicot species across a range of different biomes in eastern Australia. Mean annual temperatures ranged from 10 to 27 °C and aridity (precipitation/potential evapotranspiration) from 0·33 to 1·02 across study sites.

3. Xylem-specific conductivity, species’ height and ratio of leaf area to xylem area were positively correlated, manifesting as a single axis of trait variation, with other traits mostly orthogonal to this axis. Thus, as height and ratio of leaf area to xylem area increased across species and habitats (increasing resistance per leaf area), xylem-specific conductivity partially compensated for this resistance. Xylem-specific conductivity was well predicted by increasing height (r² = 0·45) and ratio of leaf area to xylem area (r² = 0·36). This three-trait axis was positively correlated with increasing precipitation (r² = 0·28) and temperature (r² = 0·15), but most of the explained variance lay within sites (39%) rather than across sites (10%). Thus, the spread of species’ traits along this functional axis reflected structural and hydraulic differences among co-occurring species, at least as much as it reflected differences associated with contrasting climates.

4. High xylem-specific conductivity in stems was accomplished by high vessel diameter to number ratio (r² = 0·32) and/or by high vessel lumen fraction (r² = 0·13). Low midday water potential (higher xylem tension) was associated with low ratio of vessel diameter to number (r² = 0·25), whereas low specific gravity (r² = 0·18) and stiffness (r² = 0·12) were associated with high vessel lumen fraction.

5. Light capture (i.e. increasing height and leafiness) may be facilitated by high xylem-specific conductivity, but marked increases in xylem-specific conductivity may also be associated with reduced hydraulic and mechanical safety. Although the trade-offs associated with increasing xylem-specific conductivity remain unclear, our data suggest that xylem-specific conductivity is important for maintaining water balance across a large range of species and biomes.

1. Prey species often possess defences (e.g. toxins) coupled with warning signals (i.e. aposematism). There is growing evidence that the expression of aposematic signals often varies within species and correlates with the strength of chemical defences. This has led to the speculation that such signals may be ‘honest’, with signal reliability ensured by the costliness of producing or maintaining aposematic traits.

2. We reared larval seven-spot ladybirds (Coccinella septempunctata) on a Low or High aphid diet and measured the effects on warning signal expression (elytral carotenoid pigmentation, conspicuousness, spot size), levels of defensive alkaloids (precoccinelline, coccinelline), and relationships between these traits.

3. High-diet individuals had greater total precoccinelline levels, and elytra carotenoid concentrations at adulthood which was detectable to a typical avian predator. However, larval diet did not significantly affect adult body mass or size, spot size or coccinelline levels.

4. Elytra carotenoid concentrations correlated positively with total precoccinelline levels in both diet groups and sexes. However, the relationship between elytra carotenoid concentrations and total levels of coccinelline depended on sex: in both diet groups, elytra carotenoids and coccinelline levels were positively correlated in females, but negatively correlated in males. Spot size and coccinelline levels correlated positively in Low-diet individuals, but negatively in High-diet individuals.

5. These results point to physiological linkages between components of aposematism, which are modulated by resource (i.e. food) availability and affect the honesty of signals. Developmental diet, but also sex, influenced the relationships between signals and toxin levels. Ladybirds are sexually size dimorphic, and thus in comparison with males, females may be more susceptible to resource limitation and more likely to be honest signallers.

1. With the global increase in CO₂ emissions, there is a pressing need for studies aimed at understanding the effects of ocean acidification on marine ecosystems. Several studies have reported that exposure to CO₂ impairs chemosensory responses of juvenile coral reef fishes to predators. Moreover, one recent study pointed to impaired responses of reef fish to auditory cues that indicate risky locations. These studies suggest that altered behaviour following exposure to elevated CO₂ is caused by a systemic effect at the neural level.

2. The goal of our experiment was to test whether juvenile damselfish Pomacentrus amboinensis exposed to different levels of CO₂ would respond differently to a potential threat, the sight of a large novel coral reef fish, a spiny chromis, Acanthochromis polyancanthus, placed in a watertight bag.

3. Juvenile damselfish exposed to 440 (current day control), 550 or 700 μatm CO₂ did not differ in their response to the chromis. However, fish exposed to 850 μatm showed reduced antipredator responses; they failed to show the same reduction in foraging, activity and area use in response to the chromis. Moreover, they moved closer to the chromis and lacked any bobbing behaviour typically displayed by juvenile damselfishes in threatening situations.

4. Our results are the first to suggest that response to visual cues of risk may be impaired by CO₂ and provide strong evidence that the multi-sensory effects of CO₂ may stem from systematic effects at the neural level.

1. Arctic ecosystems are experiencing rapid climate change, which could result in positive feedbacks on climate warming if ecosystem carbon (C) loss exceeds C uptake through plant growth. Bryophytes (mosses, liverworts and hornworts) are important components of Arctic vegetation, but are currently not well represented in terrestrial C models; in particular, seasonal patterns in bryophyte C metabolism compared to vascular plant vegetation are poorly understood.

2. Our objective was to quantify land-surface CO₂ fluxes for common sub-Arctic bryophyte patches (dominated by Polytrichum piliferum and Sphagnum fuscum) in spring (March–May) and during the summer growing season (June–August) and to develop a simple model of bryophyte gross primary productivity fluxes (P_B). We use the model to explore the key environmental controls over P_B for P. piliferum and S. fuscum and compare seasonal patterns of productivity with those of typical vascular plant communities at the same site.

3. The modelled total gross primary productivity (ΣP_B) over 1 year (March – November) for P. piliferum was c. 360 g C m⁻² ground and for S. fuscum c. 112 g C m⁻² ground, c. 90% and 30% of total gross primary productivity for typical vascular plant communities (ΣP_V) over the same year. In spring (March–May), when vascular plant leaves are not fully developed, ΣP_B for P. piliferum was 3 × ΣP_V.

4. Model sensitivity analysis indicated that bryophyte turf water content does not significantly affect (March–November) ΣP_B for P. piliferum and S. fuscum, at least for periods without sustained lack of precipitation. However, we find that seasonal changes in bryophyte photosynthetic capacity are important in determining ΣP_B for both bryophyte species.

5. Our study implies that models of C dynamics in the Arctic must include a bryophyte component if they are intended to predict the effects of changes in the timing of the growing season, or of changes in vegetation composition, on Arctic C balance.

1. The temperature-size rule (TSR) is a widespread phenomenon, which describes the phenotypic plastic response of species’ size to temperature: individuals reared at colder temperatures mature as larger adults than at warmer temperatures.

2. The TSR is driven by an unequal thermal response of growth and development rates. However, we currently lack an understanding of how these rates change through ontogeny and their decoupling. Further, we do not know how this decoupling varies across generations.

3. Using the brine shrimp Artemia franciscana as a model, we examine growth and development rates through ontogeny at different temperatures across two generations.

4. The slopes of natural-logged weight-specific growth rates against temperature are steeper in earlier than later larval stages, indicating their greater temperature dependence, whereas development rates maintain the same temperature dependence across life stages. An inverse TSR is generated in early larval stages; the typical TSR (smaller size at warmer temperatures) is only established later in ontogeny.

5. Phase-specific temperature dependence of growth and development rates is not significantly different across the 1st and 2nd generation, suggesting the TSR is primarily a within-generation outcome.

6. Ontogenetic size responses in Artemia are compared to other crustacean species to identify patterns within this subphylum. Data for a range of crustaceans follow the same ontogenetic pattern: early larval stages show an inverse or no TSR, with TSR being only established in later stages. Adults often, but not always, show the greatest response.

1. How predators and prey distribute themselves across space can have large population and community-level consequences by affecting the frequency and potential strength of interactions between and within trophic levels. The general pattern that emerges from numerous studies is that predators seek areas with higher prey densities and prey avoid areas with higher predation risk. However, little is known about the behavioural mechanisms underlying the emergent spatial patterns between freely interacting predators and prey.

2. We examined the behaviour and space use of groups of Pseudacris regilla (Pacific treefrog) tadpole prey and larval Rhionaeschna multicolor (blue-eyed darner) odonate predators in arenas consisting of four patches of the prey’s resources divided into two spatial scales over two observation periods a day apart. Distributions were assayed both alone and together. We predicted scale should inherently affect the resulting spatial patterns because factors such as selection, competition, interference, movement ability and prey responses to predators all have potentially similar effects as scale become larger or smaller. These factors predict that prey should be more able to dictate the spatial pattern at smaller scales and predators at larger scales.

3. Results generally match these predictions with measures of joint space being consistent with the predators dictating the joint space use more than expected at the larger scale. Moreover, at the smaller scale, either the predator and prey responses offset or reverse to favour the prey. We used a model selection approach to look at the underlying behavioural rules shaping these spatial patterns. Prey were more likely to leave patches with lower resources across both scales. However, their response to predators and competitors differed between the scales, with prey appearing to become trapped with predators only at the larger scale and only avoiding other prey at the small scale.

4. These results highlight the importance of investigating freely interacting predators and prey and the factors that are likely to affect the predator’s or prey’s ability to dictate spatial patterns. An ability to predict predator–prey spatial outcomes should be a great benefit with habitat fragmentation and shifting population densities, distributions and community compositions.

1. Maintaining a high and stable body temperature is often critical for female ectotherms during reproduction. Yet this strategy may be energetically costly, and therefore challenging, during this period of already high-energy demand.

2. Here, the 6-week deployment of tri-axial accelerometers (n = 6) on a marine ectotherm, the loggerhead turtle (Caretta caretta), reproducing at the northern limit of the species’ breeding range (i.e. in a thermally dynamic environment) revealed the behavioural mechanisms underlying its energy management strategy during the breeding season.

3. The estimated activity levels of female loggerheads using overall dynamic body acceleration (ODBA) were high during the breeding season, suggesting that marine turtles may not be able to remain inactive for long periods in the same manner as terrestrial ectotherms, because of the thermally dynamic nature of their environment.

4. However, activity levels were not constant throughout the season, being impacted by both ambient water temperature and female reproductive status. In cold water at the beginning of the nesting season, high levels of activity suggested that females behaviourally thermoregulated by seeking out warm water patches along the shoreline. Interactions with male turtles (courtship and/or avoidance) may also explain this high level of activity. As sea temperatures warmed up and the amount of energy devoted to reproduction probably increased, the turtles spent more time resting during long sequential flat-bottomed dives, and reduced any unnecessary locomotory activity.

5. Turtles may therefore adjust their activity patterns in response to seasonal variations in abiotic (i.e. ambient temperature) and biotic (i.e. reproductive status) factors. This may help minimize activity-linked metabolic rate and maximize reproductive output over a season while breeding in thermally dynamic environments.

6. A mechanistic model gave support to these empirical results. The model revealed that actively maintaining high and stable body temperature is of clear benefit to female turtles at temperate breeding sites. While energetically costly, such active thermoregulatory behaviour may speed up egg maturation, allowing turtles to initiate nesting earlier in the season, and hence maximize reproductive output.

1. Immune activity may be a cause of resistance to parasites, but it can also be a consequence of infection. Thus, the adaptive significance of an immune response is more accurately assessed when it is measured alongside both host fitness and infection status.

2. We sought to determine the significance of immune responses in a naturally coevolving host–parasite system in the wild, with support from laboratory experiments. We measured haemocyte numbers in Daphnia magna in relation to an infection that has a clear fitness consequence: infection with the bacterium Pasteuria ramosa causes sterilization.

3. Haemocyte number was consistently elevated in infected Daphnia in the field and in parasite exposed or infected hosts in the laboratory. Thus, elevated haemocyte numbers were essentially a symptom of infection, and we found no evidence that haemocytes help hosts exclude the parasite.

4. Consequently, these results provide an especially clear example where increased immune activity does not mean increased immunity or fitness: hosts with the highest haemocyte counts have extremely low health and low fitness potential.

1. Although competition for pollination is often invoked as a driver of broad-scale evolutionary and ecological patterns, we still lack a clear understanding of the mechanics of such competition. When flower visitors alternate between two species of flower, heterospecific pollen transfer takes place. The impact of these mixed loads on the female reproductive success of a recipient has received considerable attention, but the concomitant loss of male reproductive success – because of pollens grains being lost to foreign stigmas – has received less. Furthermore, pollen losses are not limited to grains that land on stigmas, but can also include deposition on non-stigmatic surfaces of the intervening flowers, or loss from the animal’s body through passive detachment or active grooming. We collectively term these losses because of competition ‘pollen misplacement’.

2. Here, we quantify pollen transferred by nectar bats between focal flowers (Aphelandra acanthus) with and without intervening visits to one of two competitor species. One competitor (Centropogon nigricans) places its pollen in the same region of bats’ heads as the focal species, while the other (Burmeistera sodiroana) places its pollen farther forward.

3. We found that (i) any intervening visit caused some reduction in the number of pollen grains transferred, (ii) competitor flowers with similar pollen-placement locations caused greater reductions in pollen transfer and (iii) of these competitors, those in male phase (dispensing pollen) caused greater pollen loss than those in female phase (without pollen).

4. This study provides rare empirical support for the detrimental effects of competition for pollination on male fitness via pollen misplacement and is the first to show an added cost imposed by male-phase competitors. Although this competition is especially strong when competitors overlap in pollen placement, diverging in pollen placement will not completely eliminate pollen loss during visits to foreign flowers, simply because pollen sheds or is groomed from pollinator’s bodies at some background rate over time. This suggests that any angiosperms that share pollinators face pervasive selection through male fitness to diverge in floral traits, alleviating competition by attracting different pollinators, altering floral phenology or encouraging floral constancy.

1. Arbuscular mycorrhizal fungi (AMF) have been proposed as a mechanism to reduce nutrient inputs in agriculture, thereby reducing costs and increasing environmental sustainability. However, before this can be achieved, we need to gain a better understanding of the importance of the prolonged selective pressures acting on indigenous AMF communities.

2. Much research concentrates on short-term ecological soil × plant × AMF interactions. However, we have little understanding of how long-term manipulations of abiotic conditions can be strong selection agents for AMF communities. Here, we ask how the long-term management of soil fertility and fertilizer use can influence the AM symbiosis. More specifically, we investigated whether 70 years of consistently imposed nutrient limitations affected the structure and symbiotic functioning of indigenous AMF communities.

3. Using the long-term Static Nutrient Deficiency Experiment carried out since 1937 in Thyrow, Germany, with and without nitrogen (N) and phosphorus (P) additions, we addressed the following questions: (i) Do different soil fertilizer treatments affect the overall abundance and diversity of indigenous AMF in an agricultural field; and (ii) Does the depletion of a nutrient select for an enhanced AMF ability to supply the deficient nutrient?

4. We assessed AMF spore diversity in the field and established a common garden experiment where soil nutrient treatments were calibrated against those in the long-term field experiment. For each soil nutrient treatment, we compared the growth responses of barley plants to the indigenous AMF communities isolated from the different soil fertilization treatments in the field.

5. We found that the long-term use of specific soil fertilization treatments altered the effects of the AMF symbiosis on plant and fungal growth. Consistent with the optimal foraging theory, AMF from N- or P-deficient soils grew larger but reduced plant growth more in those conditions relative to AMF isolated from non-deficient soils. This could result from both community-level changes and/or adaptations within species.

6. Thus, we propose that the ongoing agronomic management of abiotic selective pressures such as soil fertility needs to be considered as a strong determinant of AMF symbiotic functioning.

1.  Investment in reproduction is anticipated to be costly and can decrease survival or future reproductive success. For males, substantial reproductive costs may be accrued when competing for mates, particularly when individuals need to invest heavily in the production of sexual signals to attract females. On a proximate level, increased male signalling effort can cause somatic damage because of oxidative stress, although this has been demonstrated only in species with visual sexual signals.

2.  We tested whether reproductive effort (comprising reproduction, aggression and scent signalling) is associated with increased oxidative stress in male house mice (Mus musculus domesticus). Sexual signalling in this species involves the production and deposition of scent signals containing a high concentration of protein around a defended territory. Male reproductive investment was manipulated by housing males alone, with a female or with a female and in the vicinity of competitors.

3.  Males breeding in the vicinity of competitors invested the most in olfactory signalling as well as having regular aggressive interactions with other males. These males tended to show greater oxidative damage to lipids in the gastrocnemius muscle but no other indication of increased oxidative stress. Instead, lipid oxidation was lower in the serum and liver of reproductive males compared with those housed alone.

4.  Our results highlight that oxidative stress does not always occur simply as a function of increasing reproductive effort. The lack of a consistent increase in oxidative damage could be due to adaptive regulation of antioxidants and/or a consequence of the scent signalling system of house mice, which differs considerably from the visual signalling of birds previously examined in this context.

1. Bogs are nutrient-poor peatland ecosystems that are sensitive to nitrogen (N) deposition. Production of peat mosses (i.e. the peat-forming genus Sphagnum) is known to decrease under elevated N deposition, but the causal mechanisms are poorly understood.

2. It is predicted that increased N deposition will cause changes in Sphagnum species composition, with fast-growing species benefiting from increased N availability in contrast to slow-growing species. Knowledge of species-specific responses to N availability can help us to understand interspecific competitive relationships.

3. We investigated the direct effects of N application on plant physiology in three Sphagnum species by exposing shoots to a range of N doses (corresponding to depositions of 0–5·6 g m⁻² year⁻¹), over 5 months, in a greenhouse experiment. The species investigated included one that grows high above the water-table (Sphagnum fuscum) and two that grow lower down (Sphagnum balticum and Sphagnum fallax). S. fuscum and S. balticum originate from ombrotrophic and S. fallax from minerotrophic environments. To estimate N responses, we measured the performance and light-capture kinetics of the photosynthetic apparatus (maximum photosynthetic rate and F_v/F_m), biomass production, shoot formation, and N and phosphorus (P) concentrations in the tissue.

4. Tissue nitrogen concentration generally increased with N application rate, and photosynthetic rate increased with N concentration, although S. balticum exhibited a unimodal response. With respect to production, a negative response to N application rate was found in S. fallax and S. fuscum (weak), while production in S. balticum was unrelated to application rate. S. fallax was the fastest-growing species, producing two to three times more biomass per shoot compared with the other species.

5. The mismatch between photosynthetic capacity and production could partly be explained by an increased N : P ratio following N application. Phosphorus limitation may not negatively affect photosynthetic capacity, but may hamper production.

6. The fast-growing species S. fallax is considered to benefit from increased N deposition, but we found a negative physiological response, suggesting stoichiometric constraints. Thus, we conclude that responses to N deposition cannot be predicted in a simple way from physiological traits related to growth rate without considering local environmental factors.

1. Resource availability can influence the structure of animal communities by mediating competitive interactions. An underappreciated aspect of resource ecology is how functional traits are built from particular sets of nutrients and thus are underexpressed when those nutrients are scarce.

2. One idea linking resource availability to competition is the metabolic fuel hypothesis, which posits that access to carbohydrate-rich resources favours high activity rates that increase competitive prowess. One prediction of this hypothesis is that an increase in dietary carbohydrate richness will lead to an increase in consumer metabolic rate (MR). An alternative prediction is that carbohydrate-rich diets will affect biochemical storage.

3. We tested these predictions by examining the effect of dietary protein : carbohydrate (P : C) ratio on the feeding behaviour, demography, physiology and MR of colonies of Ectatomma ruidum, a common tropical ant. We found that rearing colonies for 6 weeks on different P : C diets altered colony demography and worker storage biochemistry, but higher carbohydrate intake did not result in an increase in whole-colony MR.

4. Our results suggest that dietary carbohydrates may increase colony dominance through changes in colony composition and individual worker longevity rather than changes in worker activity rates. More generally, they illustrate how the identity of scarce nutrients can have particular effects on traits that impact ecological interactions.

1. Indirect induced plant defence via emission of herbivore-induced plant volatiles (HIPV) to recruit natural enemies of herbivores is a ubiquitous phenomenon, but whether and how emission of above-ground HIPVs is adaptively modulated by below-ground mutualistic micro-organisms is unknown.

2. We investigated the effects of the mycorrhizal fungus Glomus mosseae on chemical composition of HIPVs emitted by bean plants Phaseolus vulgaris attacked by spider mites, Tetranychus urticae, using proton-transfer mass spectrometry, and attraction of the spider mites’ natural enemy, the predatory mite Phytoseiulus persimilis, to these HIPVs using a Y-tube olfactometer.

3. Mycorrhiza significantly changed the HIPV composition. Most notably, it increased the emission of β-ocimene and β-caryophyllene, two compounds synthesized de novo upon spider mite attack. The constitutively emitted methyl salicylate was increased by spider mite infestation but decreased by mycorrhiza.

4. The predators responded strongly to HIPVs emitted by plants infested for 6 days and preferred HIPVs of mycorrhizal plants to those of non-mycorrhizal plants. In contrast, they were less responsive and indiscriminative to mycorrhization when exposed to volatiles emitted by non-infested plants and plants infested by spider mites for 1 or 3 days.

5. Our study provides a key example of an adaptive indirect HIPV-mediated interaction of a below-ground micro-organism with an above-ground carnivore.

1. Sexually selected traits often honestly advertise aspects of individual quality, such as immune function. Such traits have traditionally been thought to reveal real-time information (e.g. current health state), but they may also reflect immunological conditions experienced during ontogeny, which can fundamentally shape survival prospects, adult immune function, and reproductive performance.

2. We tested the effects of immune challenges (injections of sheep red blood cells) during neonatal development on adult immune function and ornamental coloration in male mallard ducks (Anas platyrhynchos). Mallards have a carotenoid-pigmented beak that plays a role in mate choice, and because carotenoids are also associated with immune responsiveness, carotenoid accumulation in body tissues may change as a function of immunological state during development and into adulthood.

3. We found that mallards that received immune challenges at the completion of growth (8–10 weeks old) had a reduced proinflammatory response (as measured by the local swelling response to phytohemagglutinin; PHA) as adults, compared to control birds and those receiving immune challenges at other developmental time points. Mallards that received immune challenges during the acquisition of nuptial plumage (13–15 weeks old) had an increased humoral immune response as adults, as assessed by antibody production to keyhole limpet hemocyanin (KLH). Body mass, adult beak colour, and carotenoid circulation were not affected by immune challenges issued at any point during development.

4. Circulating carotenoid levels prior to adult immune challenge and change in carotenoid titre over the course of the adult immune assessment period were correlated with degree of response to PHA and KLH at adulthood, as well as with nitric oxide production, which is associated with innate immunity. However, the direction of these correlations varied by type of immune assessment. Surprisingly, unlike in several previous studies, we found no link between beak coloration and adult immune function.

5. These findings demonstrate the importance of developmental immune challenges in shaping adult immune response, although the precise mechanisms remain unidentified. Moreover, we found support for the hypothesis that carotenoids are linked to immune function, because of the relationship between multiple immune responses and both initial and change in circulating carotenoid levels.

6. However, our study does not support the hypothesis that sexual signal expression reveals developmental immune history. Taken together, our findings suggest that the relationships between carotenoid physiology, carotenoid-based ornamentation, and immune function are complex.

1. In oviparous species providing maternal care, the choice of nest site is crucial for the survival of both the eggs and the mother. Most embryos only develop successfully within a narrow range of incubation conditions, which may differ from the mother’s own requirements.

2. How, then, do nest-attending mothers select sites that provide suitable conditions for embryonic development, without compromising their own viability?

3. We investigated nest-site selection in flat-rock spiders, Hemicloea major, a species that guards fixed egg sacs in a thermally challenging environment (under sun-exposed rocks). Females glue egg sacs beneath rocks during late spring and guard their eggs during summer, when temperatures beneath rocks often exceed 50 °C.

4. Our field surveys show that spiders laid eggs beneath rocks that were larger and thinner, and thus hotter, than were most available rocks. However, the egg sacs almost invariably were glued to the coolest sites on the substrate beneath a rock, rather than to the (hotter, by about 9 °C) underside of the rock.

5. By affixing their egg sacs to the coolest locations beneath the hottest rocks, females ensured that their developing offspring experienced moderate temperatures and avoided lethal extremes and, simultaneously, gave themselves access to much hotter areas (that enhance their feeding and growth rates) under the same rock. This strategy allows mobile adult spiders to actively select higher temperatures than can be tolerated by their embryos, while remaining close enough to their eggs for effective nest guarding.

1. The developmental environment plays a key role in determining offspring phenotype, and the parents’ behaviour and physiology often dictates developmental conditions. Despite the plethora of studies documenting the importance of incubation temperature on offspring phenotype in reptiles, very few studies have examined such relationships in birds.

2. Because nearly all birds physically incubate their eggs, altering the nest environment may be an important but previously overlooked way parents can influence their offspring’s phenotype. Here, we tested the hypothesis that incubation temperature would affect thermoregulation in wood duck (Aix sponsa) hatchlings.

3. We show that a reduction in <1 °C in incubation temperature affects the metabolic costs of thermoregulation in offspring of a non-domesticated bird, resulting in 27–40% greater increases in oxygen consumption of ducklings incubated at the lowest temperature relative to ducklings incubated at higher temperatures.

4. Because we demonstrate that incubation temperature affects hatchling phenotypic quality, our findings provide novel support for newly proposed frameworks that highlight the importance of incubation temperature to the evolution of clutch size in birds.

1. Inverted click-beetles (Elateridae) jump to right themselves, providing enough energy to launch the body many body lengths into the air.

2. We tested whether the apparently redundant jump energy could be an adaptation for jumping from compliant surfaces that absorb energy, in the natural habitat. Jump height was measured in beetles jumping from natural substrates and from an apparatus we designed, allowing them to adjust the level of jump energy attenuated by the substrate.

3. Jump height was dramatically reduced (by c. 75%) when jumping from leaves that covered approximately half of the study site. In the remaining area, jumping for righting was either not required or not substantially attenuated. Therefore, the available power for jumping results in low jumps that are barely sufficient for righting when jumping from compliant surfaces covering c. 50% of the natural habitat.

4. The decrease in jump height was correlated with the amount of work absorbed by the substrate. We therefore conclude that the beetles do not adjust the muscle work invested in jumping to adjust for changes in substrate stiffness.

5. Scaling considerations of the jumping mechanics suggest that substrate compliance becomes a bigger problem for larger beetles.

6. The effect of substrate compliance needs to be taken into account while addressing the functional ecology of jumping animals.

1. Understanding the proximate and ultimate mechanisms shaping the expression of alternative reproductive phenotypes is a fundamental question in life-history evolution. Precocial maturation in fishes, one such alternative phenotype, has been thought to reflect rapid growth and/or energy accumulation; however, mechanistically linking these specific traits to discrete life-history patterns is complex and poorly understood.

2. Here, we use growth hormone (GH) transgenic Atlantic salmon to elucidate the effects of intrinsically fast growth on precocial male maturation as parr (freshwater life stage). Despite facilitating growth to sizes typical of mature wild-type parr, transgenesis did not influence maturation in the first year of life. In the second year, the number of maturing transgenic parr was only half that of non-transgenic individuals.

3. By manipulating intrinsic growth and controlling for both environment and genetic background, this study provides direct empirical evidence suggesting that the physiological mechanisms promoting growth do not play a causative role in precocial male maturation in fishes.

4. In addition, this study provides the first empirical data on the relative incidence of precocial male maturation in GH transgenic and non-transgenic Atlantic salmon and, therefore, provides valuable information for the ecological risk assessment process.

1. Variation in the effectiveness of mutualistic associations is well characterized in plant–soil symbiont interactions, yet there are little empirical data providing insight into how such variation evolves and persists in natural settings.

2. Heterogeneity in the strength and direction of co-evolutionary selection among spatially discrete demes is predicted to be important for the maintenance of genetic variation in species interactions. Here, we experimentally test the potential for local adaptation to generate phenotypic divergence among wild host–symbiont populations using two leguminous host species that differ in their specificity for rhizobial partners.

3. Molecular characterization of host populations and associated rhizobial communities revealed significant among-population genetic differentiation. Reciprocal cross-inoculation experiments testing for variation in the fitness of nine populations of Acacia salicina and A. stenophylla in response to inoculation with rhizobia revealed variation in host response to the mutualism (both host species), and the benefit conferred by different rhizobial populations (A. salicina only). However, there was no indication that host population-by-rhizobial population interactions influence the outcomes of mutualism for the host.

4. We further examined potential correlations between (i) plant response to inoculation and (ii) rhizobial effectiveness, with variation in soil fertility at the sites from which plant and rhizobial samples originated. Data from the cross-inoculation experiments revealed no correlations between soil chemistry, water availability and either host or rhizobial performance. However, analysis of results from an extensive whole-soil inoculation trial including nearly 60 A. salicina and A. stenophylla sites showed a significant negative correlation between levels of soil nitrogen and plant response to inoculation.

5. Overall, these findings suggest that selection for local adaptation may play little role in maintaining phenotypic variation in these interactions. We hypothesize that mutualistic interactions occurring among communities of hosts and symbionts do not favour co-evolutionary divergence among populations.

1. According to a recent hypothesis, personality traits should form integrative pace-of-life syndromes with life-history traits. Potential life-history traits that explain personality variation are immune defence and growth rate.

2. We studied whether boldness, measured as hiding behaviour, is repeatable during ontogeny in the field cricket, Gryllus integer, and if it relates to the efficiency of immune function (i.e. the capacity to encapsulate a nylon implant), growth rate, developmental time and size as an adult.

3. Hiding behaviour was rank-order repeatable, and in general, juveniles were bolder than adults. Individuals that were cautious at early juvenile stages had higher encapsulation responses late in life compared with bold individuals. Most clearly, fast-growing individuals matured early and invested little in immune defence compared with their slower-growing conspecifics, i.e. showed patterns of a ‘grow fast, die young’ life-history strategy.

4. Our results may arise from a trade-off between immunity-dependent survival and bold behaviour. Trade-offs between investment in survival and behaviour could account for the maintenance of variation in personality traits by favouring certain combinations of behavioural and life-history strategies (i.e. pace-of-life-syndromes).

1. The ecology of endotherms is driven by their great energetic need for thermoregulation, which renders mammals and birds particularly vulnerable to environmental temperature and resource fluctuations. Important outstanding questions are whether populations are specialized to their particular climate, and to what extent gene × environment interactions determine thermal responses.

2. Here, we show that phylogenetic relatedness and climate interact to determine metabolic capacities, body temperature and morphology in a wild rat (Rattus fuscipes).

3. Mitochondrial metabolic capacities are greater in warm climate populations, indicating that these responses are not the result of cold adaptation. However, glycolytic capacities, fur thickness and capacity for nonshivering thermogenesis are greater in cool climate populations. In populations from cooler climates, body temperatures are lower, but more variable. Together, these changes lead to substantial energy savings in cool climate populations, although all traits are constrained by phylogenetic relatedness.

4. We demonstrate for the first time that gene × environment interactions determine thermal responses in wild mammal populations, and we suggest that physiological variability among populations may render the species more resilient to climate change because it increases whole-species performance breadth. Climate envelope modelling is therefore insufficient to predict the future impact of climate change.

1. Interactions between primary producers and consumers (i.e. grazers) are of fundamental importance to the successful functioning of ecological communities. Plant–herbivore interactions have been extensively studied, and herbivory has been accepted as an important process contributing to the structure of terrestrial and aquatic ecosystems. In contrast, the functional importance of the ecologically equivalent interaction between scleractinian reef corals and polyp-feeding fishes is largely untested, but has generally been dismissed as unimportant.

2. This study quantified the amount of tabular acroporid coral tissue biomass consumed at the population level by corallivorous butterflyfishes and determined the proportion of both the standing biomass and productivity that is consumed annually at three exposed reef crest sites at Lizard Island, Great Barrier Reef and Australia.

3. Total daily coral consumption ranged from 18·6 (±1·6) to 27·4 (±1·5) g 200 m⁻² day⁻¹ with 61–68% of this consumption directed towards tabular acroporid corals. This selective feeding resulted in an annual consumption of between 8·9–13·5% of the total available tissue biomass and between 52–79% of the annual productivity of these tabular acroporid corals.

4. The proportion of standing coral tissue biomass removed by corallivorous butterflyfishes is similar to that removed from terrestrial plants by herbivores. However, the proportion of primary productivity consumed is considerably greater on coral reefs for both corallivorous and herbivorous fishes compared with terrestrial systems.

5. In terrestrial systems, even relatively low levels of defoliation can have significant effects on plant growth rates, seed production and overall fitness. Considering the high proportion of productivity that is consumed by polyp-feeding fishes, it would seem incongruous that these grazing fishes do not have similar effects on coral community structure and population dynamics. Our findings highlight the need to revisit previously held assumptions regarding the functional importance of corallivorous fishes to coral reef ecosystems.

1. The capacity to adapt to low temperature is critical for the persistence of insect populations in heterogeneous environments. Locusts show remarkable phenotypic plasticity, termed ‘phase change’, in response to local population density.

2. In this study, the hypothesis that population density, as a social factor, affects the cold hardiness of progeny is validated in the migratory locust, Locusta migratoria, which shows remarkable density-dependent phase changes between gregarious and solitarious phases.

3. We demonstrated that eggs of gregarious and solitarious migratory locusts significantly differ not only in size and weight, but also in cold hardiness. Eggs of solitarious locusts are more resistant to cold stress compared with those of gregarious locusts, with longer 50% lethal time at different low temperatures and under different acclimation treatments of cooling rates or cold exposure time, lower upper limit of chill injury zone, and lower sum of injurious temperature resulting from temperature–time regression. The lowest cooling rate (0·05 °C min⁻¹) yields the highest survival of cold for eggs.

4. A custom-made microarray covering 9154 unigenes of the migratory locust demonstrated quite different gene expression profiles in the two phases in response to normal or low temperature. Under cold stress, the gregarious-phase eggs have higher transcriptional levels of heat-shock proteins, DOPA decarboxylases and tyrosine hydroxylase, whereas the solitarious-phase eggs exhibit stimulated lipid metabolism and carboxylic acid transport.

5. Hybridization between the two phases showed that the cold hardiness of eggs from the hybrid with solitarious females is significantly higher than that of the hybrid with gregarious females, and the cold hardiness of eggs from each reciprocal hybrid is close to their maternal origins. These results indicate that the cold hardiness of progeny is affected by the parental phase status.

1. Many animals use signals to resolve disputes over resources. Some signals act as reliable indicators of other traits, such as whole-organism performance or body condition, which may also be important for resolving disputes. Because of the correlations inherent in reliable signals, it is challenging to determine which variables are directly relevant for resolving aggressive interactions.

2. We examined the relationships among dewlap size, bite force and condition, all traits that may be important to conflict resolution in male green anole lizards (Anolis carolinensis). Using a large sample of wild-caught animals, we showed significant positive correlations between dewlap size and maximum bite force capacity, when each trait is corrected for its correlation with body size.

3. We tested the relative importance of each trait to the outcome of interactions in a subset of our sample. We staged dominance encounters between size-matched male green anoles after surgically reducing the dewlap size of one competitor.

4. We show that reducing the size of the dewlap does not significantly change the outcome of staged interactions. Rather, males with higher values of bite force capacity were more likely to win fights. We hypothesize that during close-proximity aggressive interactions, male green anoles use more direct means of assessing one another and that dewlap size functions as a signal of bite force primarily during long-distance territorial displays. Body condition was correlated with bite force, but did not differ significantly between winners and losers.

5. Our results show how an experimental approach can decouple reliable signals from their correlated traits to test which factors influence male contest resolution.

1. Beneficial ‘services’ in mutualistic interactions have often not evolved de novo, but from ancestral traits that had a function before the emergence of the association. These traits can then acquire novel functions in a mutualism. Even in many close insect–plant relationships, the services provided by each partner are still unclear.

2. In the well-known association between the carnivorous pitcher plant, Nepenthes bicalcarata, and Camponotus schmitzi ants in Borneo, the ants benefit by receiving food and nesting space in swollen, hollow pitcher tendrils, but the benefits to the plant are less clear. Previous studies have suggested that the ants protect against herbivory, prevent putrefaction of pitchers by removing prey items from them or increase the pitcher’s prey retention rate by attacking pitcher visitors.

3. Field observations showed that C. schmitzi ants regularly clean the pitcher rim (peristome), which is the main surface responsible for prey capture. We found that this behaviour increases the carnivorous plant’s prey capture efficiency and helps to maintain it over the pitcher’s life span. Running tests with Oecophylla smaragdina ants on colonised and ant-free older pitchers demonstrated 45·8% higher capture efficiency in pitchers inhabited by C. schmitzi. Head counts of trapped ants showed that C. schmitzi-colonised pitchers indeed captured significantly (45·2%) more prey than uncolonised pitchers of the same age.

4. The peristomes of ant-free older pitchers were strongly contaminated by fungal hyphae and other particles. Experimental contamination of clean pitcher peristomes with starch also strongly reduced capture efficiency. While the peristome was cleaned rapidly in ant-colonised pitchers and capture efficiency returned to the previous level within approximately 1 week, no cleaning and recovery were observed in ant-free pitchers.

5. Within the genus Nepenthes, N. bicalcarata has exceptionally long-lived pitchers. We propose that C. schmitzi ants benefit N. bicalcarata by keeping the pitchers effective over long periods of time, likely allowing the plant to acquire more nutrients per pitcher and thereby minimise pitcher construction costs.

6. Our findings demonstrate that the cleaning behaviour typical of many plant–ants has acquired a novel function in this ant–plant association, giving rise to a new type of myrmecotrophic mutualism.

1. Trade-offs between current and future resource allocation can select for elevated reproductive effort in individuals facing mortality. Males are predicted to benefit from increasing investment in costly sexually selected signals after experiencing an acute life span reduction, although few examples of such facultative terminal investment are known.

2. In the mealworm beetle, Tenebrio molitor, males’ odours become more attractive to females following a life-threatening immune challenge. However, the pheromones involved are unknown, hindering further insight into the proximate mechanisms and ultimate consequences of terminal investment.

3. Using chemical and behavioural analyses, we show that the cuticular hydrocarbons (CHCs) of T. molitor are sexually dimorphic and are used by females to locate and select males. Moreover, both male CHCs and glandular pheromones were affected by experimental immune challenge in a fashion that made them more attractive to females.

4. The results suggest that males terminally invest in both short- and medium-range pheromones when they perceive reduced future survival. Moreover, the constitutive and inducible aspects of male and female CHC production are consistent with sex-specific selection on the signalling and defensive functions of CHCs. The implications of terminal investment for ‘dishonest’ signalling and the efficacy of sexual selection are discussed.

1. Although ecologists commonly categorize species in terms of their functional roles, function diversity occurring at the level of the individual is often dismissed.

2. Multi-female colonies of the spider Anelosimus studiosus serve as habitat for a myriad of arthropods, and colony members display notably polymorphic behavioural tendencies: females exhibit either an ‘aggressive’ or ‘docile’ behavioural phenotype.

3. We manipulated the phenotypic composition of colonies (100% aggressive, 50% aggressive and 50% docile, 100% docile) and tested its effects on species interactions between A. studiosus and its web associates, and among the web associates themselves.

4. We found that the phenotypic composition of A. studiosus colonies significantly impacted interactions within their web. In colonies of all aggressive females, the relationship between A. studiosus (−) and its web associates (+) was exploitative and web associates negative impacted each other’s performance. In colonies of all docile females, the relationship between A. studiosus (+) and its web associates (+) was facilitative and web associates positively influenced each other’s performance. Colonies of mixed phenotype had intermediate interactions.

5. Our data suggest that (i) the mixture of behavioural trait variants within groups can mediate the nature of both direct and indirect species interactions, and (ii) community structure can affect which social group compositions enjoy highest fitness.

1. Sunlight ultraviolet (UV) exposure can be highly damaging to biological tissues, being known to cause cellular damage and immunosuppression in humans and rodents, and depletion of carotenoid-based sexual plumage coloration in birds (i.e. photobleaching). However, it remains unknown whether sunlight may cause photobleaching in living tissues that comprise sexual signals such as bare parts in birds. It seems possible that any carotenoids depleted from bare parts by sunlight could be replenished, but if so, this could impact the availability of carotenoids for other functions such as immunity and antioxidant defence. Such trade-offs seem particularly likely in individuals that have a low dietary intake of carotenoids, or small amounts of carotenoids in body storage.

2. We investigated the effects of exposure to simulated sunlight UV (UV+) on bill coloration, blood plasma and liver (i.e. body storage) carotenoids and pro-inflammatory immune responses in male zebra finches (Taeniopygia guttata) in vivo, compared with individuals maintained in an identical environment but with the UV wavelengths removed by a filter (UV−). We also investigated whether any deleterious effects of UV exposure were mitigated by dietary carotenoid supplementation (UV+ Car+).

3. Exposure to simulated sunlight UV was associated with low levels of carotenoids in liver, and elevated levels of carotenoids in blood plasma, suggesting the mobilisation of stored carotenoids. Simulated sunlight UV also caused impaired pro-inflammatory immune responses, whereas this was not seen in carotenoid-supplemented birds. We found no effects of simulated sunlight UV or carotenoid supplementation on oxidative damage in blood plasma or bill.

4. Bill ‘carotenoid chroma’ diminished, and bill ‘UV chroma’ correspondingly increased, in all groups during the experiment (i.e. even in UV+ Car+ birds, and in UV− birds). This likely arose because the illuminance in the experimental cages was far higher than in standard laboratory housing conditions and suggests that carotenoid pigmentation is highly susceptible to photobleaching even under exposure to human-visible wavelengths.

5. These results highlight the potential for sunlight exposure to invoke a range of deleterious consequences for birds, including photobleaching and depression of immunity via pathways mediated by carotenoid allocation trade-offs. The expression of carotenoid-based sexual signals may therefore reveal an individual’s history of sunlight exposure and its deleterious effects on immunity.

1. Cloud cover affects carbon exchange between biota and the atmosphere. Recent studies have demonstrated that an increase in the diffuse radiation fraction enhances the photosynthetic efficiency of canopies. Although the exact mechanism behind this effect is not clear, a more even distribution of light among leaves across the vertical profile of the canopy is considered to be the most important cause of this difference.

2. To test this hypothesis, the net ecosystem production (NEP) of a Norway spruce forest (30-year-old) was measured under cloudy and sunny skies by the eddy covariance method. In parallel, measurements of the diurnal courses of gas exchange and chlorophyll fluorescence parameters were made in the upper sun (5th whorl; 1-year-old needles), middle (8th and 10th whorl; 1- and 2-year-old needles) and lower shade (15th whorl; >2-year-old needles) shoots.

3. The higher diffuse radiation fraction during cloudy days resulted in significantly higher ecosystem carbon uptake than at corresponding incident photosynthetic photon flux density on sunny days. Our shoot-level data show that shoots from deep within the canopy contribute substantially to the overall carbon balance during cloudy days. But, although shade-adapted shoots had a markedly positive carbon balance over a 24-h period on cloudy days, their performance was impaired on sunny days contributing only a marginal or even negative carbon balance from the middle and shaded parts of the canopy. The uppermost sun shoots contributed 78% of the total carbon assimilated during a sunny day, but only 43% during a cloudy day.

4. In addition, afternoon depression of canopy NEP and CO₂ assimilation rates of the uppermost shoots (5th and 8th whorl) occurred in response to irradiance on sunny days, characterized by significant decreases in CO₂ uptake and apparent quantum yield; however, this depression did not occur under cloudy conditions. Stomatal and non-stomatal regulations of carbon assimilation in the afternoon are discussed.

1. Recent evidence indicates tight control of plant resource economics over interspecific trait variation amongst species, both within and across organs, referred to as ‘plant economics spectrum’ (PES). Whether and how these coordinated whole-plant economics strategies can influence the decomposition system and thereby impact on ecosystem carbon and nutrient cycling are yet an open question. More specifically, it is yet unknown whether plant functional traits have consistent afterlife effects across different plant organs.

2. To answer those questions, we conducted a common-garden decomposition experiment bringing together leaves, fine stems, coarse stems, fine roots and reproductive parts from a wide range of subarctic plant types, clades and environments. We measured all plant parts for the same (green and litter) plant economics traits and identified a whole-plant axis of carbon and nutrient economics.

3. We demonstrated that our local ‘PES’ has important afterlife effects on carbon turnover by driving coordinated decomposition rates of different organs across species. All organ decomposabilities were consistently controlled by the same structure-related traits (lignin, C and dry matter content) whilst nutrient-related traits (N, P, pH, phenols) had more variable influence, likely due to their contrasting functions across organs. Nevertheless, consistent shifts in elevation of parallel trait–decomposition relationships between organs indicate that other variables, potentially related to organ dimensions, configuration or chemical contents, codetermine litter decomposition rates.

4. Whilst the coordinated litter decomposabilities across species organs imply a coordinated impact of plant above-ground and below-ground litters on plant–soil feedbacks, the contrasting decomposabilities between plant parts suggest a major role for the relative inputs of organ litter as driver of soil properties and ecosystem biogeochemistry. These relationships, underpinning the afterlife effects of the PES on whole-plant litter decomposability, will provide comprehensive input of vegetation composition feedback to soil carbon turnover.

1. Plants are known to respond to heterogeneous distribution of nutrients in the soil, and they also respond to the presence of neighbouring roots. However, it is unclear whether plants are able to distinguish between these factors and adjust their root responses accordingly.

2. We investigated whether the simultaneous response to nutrient heterogeneity and competition could be predicted from the responses to these factors separately. As a null model, we hypothesized that the responses to nutrients and competition are additive and thus no interactions occur. We performed a short-term competition experiment in the greenhouse with two floodplain species in homogeneous and heterogeneous conditions. The consequences of different root distributions for nutrient uptake were tested using ¹⁵N pulse-labelling.

3. Both species responded to nutrient heterogeneity by investing significantly more roots in the nutrient-rich patch, and both species showed a significant reduction in root growth in response to competition, albeit that the reduction was much more pronounced for the grass species. For Rumex palustris, the effects of heterogeneity and competition were additive. However, the response to nutrient heterogeneity of Agrostis stolonifera was reversed by competition: instead of proliferating in the nutrient-rich patch, it significantly increased root investments in the ‘empty’ (nutrient-poor) patches. As the partitioning of total N was less asymmetric than ¹⁵N uptake from the nutrient-rich patch, it appears that these altered root investments of A. stolonifera in the ‘empty’ patches have also been functional with respect to compensating N uptake.

4. Our results suggest that root responses to nutrient distribution in a competitive environment depend on the competitive strength of the neighbouring species. The foraging response of the superior species (R. palustris) was hardly affected, but that of the inferior species (A. stolonifera) was greatly inhibited and even reversed by competition: instead of proliferating in the nutrient-rich patch, it increased root growth and foraging activity in less favourable patches. Incorporating competitive hierarchy into root foraging studies may help to explain the ambiguous results found in previous studies.

1. Plants defend and predators attack, provoking the foraging dilemma faced by herbivores and frugivores of how to eat enough without being eaten. High toxin concentration in leaves and fruits inhibits consumption, while predation risk reduces feeding opportunities, as prey forage to avoid encountering predators. Thus, both factors vary and define the quality of the landscape. How foraging animals directly quantify, compare and respond to these two costs has rarely been tested.

2. We show that free-ranging bushbabies – small, frugivorous primates – change their behaviour and use of artificial food patches based on the interplay between toxin concentration in food and patch safety. Using a titration experiment, we demonstrate that bushbabies quantify the relative costs of toxin and fear. We pinpoint where these costs are equivalent and show that animals seek food patches with the lower net cost.

3. We conclude that the ecological effectiveness of plant toxins as defence against consumers needs to be considered in the context of a landscape of fear – and the relative impact of anti-predator tactics and plant defence is strongly shaped by the concentration of these defences.

4. A corollary is that plants may benefit from fear as a substitute for their own chemical defence, adding a new dimension to the concept of indirect plant defence. Whether, from the plant’s perspective, the benefits derived from fear can be considered evolutionarily adaptive rather than simply ecologically serendipitous remains to be tested.

1. To cope with stressful environmental temperatures, organisms can enhance thermotolerance when exposed to sub-lethal temperatures before thermal stress, a phenomenon referred to as thermal acclimation. Acclimation includes different forms (developmental, gradual or rapid) that vary in ecological importance depending on patterns of diurnal and seasonal thermal variation.

2. Here, we complete a comprehensive assessment of how the different forms of acclimation based on simulated field temperatures affect cold tolerance in Drosophila melanogaster under different levels of cold stress (−4·5 °C/2 h and 0 °C/10 h).

3. We predict that (i) combinations of acclimation treatments may be particularly beneficial and (ii) benefits of different acclimation types may differ for acute vs. chronic cold stress. We also investigate whether distinct forms of acclimation promote differential molecular responses to stress.

4. Acclimation treatments had very large effects on cold tolerance and resulted in phenotypes ranging from sensitive to tolerant individuals within the specific cold stress applied (−4·5 °C/2 h and 0 °C/10 h). Acclimation also influenced expression of several genes (Hsp23, Hsp70, Hsp40, Hsp68, Starvin and Frost) during recovery from cold stress but effects depended on the nature of the acclimation treatment.

5. Cumulative effects occurred between different forms of acclimation, and these as well as the different molecular responses point to different underlying mechanisms.

6. These results highlight that combined acclimation treatments may strongly impact field stress resistance.

1. Global increases in ultraviolet-B radiation (UVBR) associated with stratospheric ozone depletion are thought to be contributing to the rapid disappearance of amphibian populations from pristine habitats around the world. Much research has been dedicated to understanding the effects of ultraviolet radiation (UVR) alone and in combination with other environmental stressors on the early life stages of amphibians. Little is known, however, of how UVR affects amphibian metabolism, or how amphibian metabolism may change in response to exposure to other stressors in addition to UVR.

2. Using a controlled laboratory experiment, we examined the independent and interactive effects of UVR and non-lethal predatory chemical cues (PCC) on the tissue and whole-animal metabolic rate (MR) and activity of striped marsh frog Limnodynastes peronii tadpoles. PCC signal risk of predation, which is a natural stressor that can cause tadpoles to alter their behaviour, morphology, and life history, and for which the metabolic cost remains little explored.

3. We found that exposure to UVR caused tissue MR to increase by 36%, but whole-animal MR to decrease by 14%, which is most likely due to tadpoles reducing their activity levels by 56%. Exposure to PCC had no significant effect on tissue or whole-animal MR, but caused tadpoles to reduce their activity levels by 36%, indicating that the whole-animal MR of tadpoles exposed to PCC is elevated relative to their activity levels. Compared with tadpoles exposed to neither stressor, tadpoles exposed simultaneously to UVR and PCC showed no change in whole-animal MR despite reducing their activity levels by 62%.

4. This research shows that, for tadpoles, there is an energetic cost associated with being exposed to UVR and PCC independently, and that this cost is greater when they are exposed to both stressors simultaneously. Our previous research has shown that exposure of tadpoles to PCC enhances the lethal effects of UVR, and the present study suggests that this synergistic interaction may arise as a consequence of the effect of these combined stressors on MR. Global increases in UVBR may therefore be contributing to amphibian population declines by compromising energy allocation towards growth and development as well as energy allocation towards coping with additional environmental stressors.

1. Timing of offspring arrival (i.e. hatching, birth or emergence from nests) is commonly shown to have strong effects on their performance through body size and prior residency effects, but less is known about how such effects differ among species. The strength of such effects tends to be related to competitive intensity (e.g. population density). Variation in timing effects among species may therefore be expected to be related to their competitive ability.

2. Here, we test this hypothesis by conducting sympatric and allopatric competition experiments in two ecologically similar salmonid species, Atlantic salmon and brown trout, at the onset of exogenous feeding. We first test the competitive ability of the two species in sympatric conditions in the absence of timing effects. We then test the strength of timing effects by manipulating this for the two species in allopatric conditions, and evaluate whether any difference in response to timing between the two species corresponds to species-specific competitive abilities.

3. In sympatry, trout outperformed salmon emerging at the same time, despite salmon being 32% larger at the time of emergence. Thus, trout was the stronger competitor.

4. In allopatric treatments, late emerging trout performed significantly poorer in terms of survival and growth than late emerging salmon. Further, dominant trout appeared better able to monopolise resources at higher competitive intensities than dominant salmon. There were also indications that population regulation was stronger in brown trout. Replicates with a high initial density of salmon ended up with twice the final density of low-density replicates, whereas trout ended up with similar final densities across treatments.

5. The results demonstrate that species-level differences in interspecific competitive ability corresponded with a higher intraspecific asymmetric competition among timing phenotypes, resulting in a higher penalty of emerging late in the more aggressive, dominant trout. Further, it suggests that intrinsic competitive abilities may affect the intensity of selection on offspring arrival, and thus likely affect evolution of phenological traits such as breeding time.

1. Populations within species often occur across divergent habitats and, under the right conditions, can adapt to local conditions. For adult and larval insects, local adaptation in tolerance traits, e.g. thermoregulation and water conservation, is well documented. Eggs of insects are immobile, non-feeding and relatively small, and therefore may be at greater risk from abiotic threats. Selection, therefore, may favour strategies that allow embryos to be robust to desiccation and thermal stresses. In particular, the canteen hypothesis predicts that eggs in hot and dry environments contain more water, and this extra water protects them from elevated rates of water loss.

2. This study tests the canteen hypothesis by (i) examining geographic patterns of egg size and water content and (ii) measuring egg and neonate performance across a range of manipulated temperatures and humidities. We focused on eggs of the hawkmoth, Manduca sexta (Lepidoptera: Sphingidae). Manduca eggs are larger in xeric regions of the United States – e.g. the southwestern deserts – compared with M. sexta eggs from eastern, mesic regions.

3. Specifically, we asked: do eggs from warmer or drier regions (i) contain more water, (ii) perform better in dry conditions and (iii) tolerate higher temperatures? We also assessed whether desiccation during the egg stage affects subsequent growth of larvae. We tested M. sexta eggs from three environments: Arizona (warm, dry), North Carolina (cool, humid) and a laboratory strain (cool, dry).

4. Although M. sexta eggs from warmer and drier populations were larger and contained more water, these changes did not protect them better from abiotic stress. Eggs from all populations were similarly tolerant of high heat and low humidity. Desiccation during the egg stage also had no long-term effects on hatchling growth rate.

5. Our results provided little support for local adaptation in abiotic stress physiology via the canteen hypothesis. However, low humidity and delayed hatching suggest a different mechanism for desiccation resistance: embryos may modify eggshell conductance in response to internal water status. The geographic cline in egg size may instead arise from selection on any of the three subsequent life stages or may reflect other evolutionary pressures on number-size trade-offs.

1. Testosterone has emerged as an important mechanism linking variation in male reproductive behaviour to parasite infection in vertebrates, and there are numerous pathways by which testosterone can influence infection risk, particularly in free-living animals.

2. The immunocompetence handicap hypothesis posits that the positive effects of testosterone on sexual signalling and behaviour are traded off with negative effects on immune function. While this obligate trade-off may sometimes explain the association between testosterone and parasite infection, testosterone–parasite relationships may also be mediated by correlated changes in stress, condition and exposure to parasites.

3. In this study, we explored associations between testosterone and reproductive behaviour, immune function and parasitism in free-living Grant’s gazelle (Nanger granti). In particular, we examined how stress (glucocorticoids), behaviour and condition might mediate associations between testosterone, immunity and parasitism.

4. We found that variation in endogenous testosterone in male gazelle was correlated with mating behaviour in terms of sexual signal intensity (horn size) and resource-holding potential (territoriality). We also showed that these same levels of testosterone were associated with immunity and parasite infection, but associations between testosterone, immunity and parasitism were complex. Testosterone was negatively associated with adaptive immunity, but positively associated with innate immunity. Relationships between testosterone and parasitism varied for different parasites.

5. Our results suggest that the effects of testosterone on male immunity are not universally suppressive and that immunoenhancement may also occur. In addition, testosterone–parasite relationships vary depending on the parasite, most likely due to the opposing effects of testosterone on different aspects of immunity and indirect effects on parasite exposure mediated by changes in behaviour.

1. Inter-individual variation in metabolic rate exists in a wide range of taxa. While this variation appears to be linked to numerous aspects of animal behaviour and personality, the ecological relevance of these relationships is not understood. The behavioural response of individual fish to acute aquatic hypoxia, for example, could be related to metabolic rate via influences on oxygen demand or the willingness to take risks. Individuals with higher metabolic rates could show greater hypoxia-associated increases in activity that could allow them to locate areas with increased oxygen availability but that also make them susceptible to predation. Any relationship between metabolic rate and risk-taking behaviour among individual fish could therefore be modulated by environmental oxygen levels, perhaps becoming stronger as oxygen availability declines.

2. We measured spontaneous swimming activity as an index of risk-taking by juvenile European sea bass in normoxia, moderate hypoxia (40% air saturation) and severe hypoxia (20% air saturation) after being startled by a predator model. All fish were also separately measured for routine metabolic rate by measuring oxygen uptake.

3. In hypoxia, fish re-emerged from cover sooner after a simulated attack and were generally more active than when the same fish were startled in normoxia. In addition, individual activity and risk-taking in severe hypoxia were positively correlated with metabolic rate. Aquatic surface respiration was a major contributor towards increased activity in hypoxia and was positively related to metabolic rate during severe hypoxia. There were no relationships between risk-taking and metabolic rate in moderate hypoxia or normoxia.

4. Relative measures of risk-taking among individual fish were not consistent among oxygen levels, further suggesting that individuals differ in sensitivity to hypoxia and the degree to which this environmental stressor affects risk-taking behaviour.

5. These results suggest that fish with relatively high metabolic rates become more active during acute hypoxia, possibly leading to increased susceptibility to predation in response to differences in metabolic demand. In addition, the relationship between metabolic rate and risk-taking may only be observable during exposure to a physiological stressor or such a stressor may strengthen any relationships observable under more benign conditions.

1. The marine intertidal zone is characterized by large variation in temperature, pH, dissolved oxygen and the supply of nutrients and food on seasonal and daily time scales. These oceanic fluctuations drive ecological processes such as recruitment, competition and consumer–prey interactions largely via physiological mechanisms. Thus, to understand coastal ecosystem dynamics and responses to climate change, it is crucial to understand these mechanisms.

2. Here we utilize transcriptome analysis of the physiological response of the mussel Mytilus californianus at different spatial scales to gain insight into these mechanisms. We used mussels inhabiting different vertical locations within Strawberry Hill on Cape Perpetua, OR and Boiler Bay on Cape Foulweather, OR to study inter- and intra-site variation of gene expression.

3. The results highlight two distinct gene expression signatures related to the cycling of metabolic activity and perturbations to cellular homeostasis. Intermediate spatial scales show a strong influence of oceanographical differences in food and stress environments between sites separated by c. 65 km.

4. Together, these new insights into environmental control of gene expression may allow understanding of important physiological drivers within and across populations.

1. Plants face threats from a variety of herbivorous insects and can use induced responses to defend themselves against these attackers. Induced responses are mediated by signal transduction involving phytohormones, such as jasmonic acid (JA) and salicylic acid (SA). Cross-talk between signal transduction pathways triggered by attackers with contrasting feeding styles allows plants to fine-tune defences. A central question in this emerging field is to understand how responses to single attackers interfere with responses to other attackers, especially by integratively addressing molecular and ecological aspects.

2. We examined the plant-mediated interactions between the leaf-chewing Pieris brassicae and the phloem-sucking Brevicoryne brassicae, and their respective parasitoids Cotesia glomerata and Diaeretiella rapae, when feeding simultaneously, sequentially or in isolation on the brassicaceous ecological model plant Brassica oleracea. We analysed the underlying defence mechanisms in the plant. Levels of the phytohormones JA and SA transcriptional responses of a number of selected defence-related genes and secondary plant compounds were quantified at different time points during the single and multiple infestations.

3. The caterpillars developed faster and reached a larger body mass on plants previously attacked by aphids. Aphids initially developed faster on plants with caterpillars, although the moment of moulting to adults was independent of the presence of caterpillars. Both parasitoid species performed better under multiple-infestation scenarios than in single-herbivore situations.

4. On plants attacked by aphids, the JA levels were tenfold lower than on undamaged plants or plants with caterpillars. Additionally, the low transcript levels of LOX and MYC, genes coding for a JA biosynthesis-related enzyme and a transcription factor, respectively, in aphid-infested plants, suggest that the facilitation of the caterpillar performance was mediated by interference in signal transduction. Levels of carbon and nitrogen and secondary plant compounds (glucosinolates) did not differ significantly between treatments, suggesting that these compounds did not mediate the facilitation.

5. Our data show that the leaf chewer and phloem feeder asymmetrically interact not via competition as would be expected from interspecific herbivores but instead via facilitation; the phloem feeder attenuated JA-related plant defences, thus facilitating the growth and development of the leaf chewers. In linear bitrophic systems, interactions between JA and SA signalling pathways have been proposed to allow plants to fine-tune their defences, but if facilitation frequently occurs in interspecific interguild interactions among herbivores this may represent an important constraint for plant defences. Such a constraint might be reduced if, as in our model system, parasitoids also benefit from interactions between interguild hosts and nonhosts, but parasitoids are rarely considered in model molecular systems to assess the impact of herbivore-induced plant defences.

1. Life histories, population dynamics and geographic range limits are fundamentally constrained by the way organisms acquire and allocate energy and matter. Metabolic theories provide general, parameter-sparse frameworks for understanding these constraints. However, they require the accurate estimation of body temperature which can be especially challenging in terrestrial environments.

2. Here, I integrate a metabolic theory (Dynamic Energy Budget theory, DEB) with a biophysical model for inferring field body temperatures and activity periods of terrestrial ectotherms and apply it to study life-history variation and geographic range limits in a widespread North American lizard, Sceloporus undulatus.

3. The model successfully predicted trait co-variation (size at maturity, maximum size, reproductive output and length-mass allometry) through changes in a single parameter. It also predicted seasonal and geographic variation in field growth rates, age at first reproduction, reproductive output and geographic range limits (via r_max estimates), all as a function of spatial climatic data. Although variation in age at maturity was mostly explained by climate, variation in annual reproduction was largely a product of local body size.

4. Dynamic Energy Budget metabolic theory is concluded to be a powerful and general means to mechanistically integrate the dynamics of growth and reproduction into niche models of ectotherms.

1. Population size is often regulated by density dependence, that is negative feedbacks between growth and population density. Several density-dependent mechanisms may operate simultaneously in a population.

2. In this study, I focus on two different mechanisms of density-dependent population regulation, resource exploitation (RE) and density-dependent sexual reproduction (DDS).

3. I analyse both mechanisms in clonal populations of the rotifer Brachionus calyciflorus, which differ in the investment in sex because of a polymorphism at a single Mendelian locus. Some clones were cyclical parthenogens (CP) and possessed both mechanisms of population regulation (RE + DDS), while other clones were obligate parthenogens (OP) and thus lacking the DDS mechanism.

4. Equilibrium population size was considerably lower in CP clones, compared with OP clones, regardless of the exact measurement variable for population size (numbers of individuals or total biovolume/biomass). Interestingly, the decrease in population size was most pronounced in CP clones that heavily invested in sexual reproduction.

5. This suggests that the DDS mechanism can significantly contribute to population regulation and that genotypes lacking this mechanism (because of a mutation in genes affecting this trait) reach substantially higher population sizes. Apparently, the DDS mechanism operates already at much lower population densities than the RE, causing CP populations to stop growing before they are limited by resources.

6. As these differences in population regulation were caused by genetic variation within a single species and as rapid selective sweeps by OP clones are common in B. calyciflorus, this study provides an example for an eco-evolutionary feedback on an important ecological variable – equilibrium population size.

1. Human-induced impoverishment of pollinator faunas may affect plant–pollinator interactions and limit pollen availability. Under these conditions, chronic outcross pollen limitation is expected to select for floral characters that maintain seed production, including autonomous selfing.

2. In this study, the impact of anthropogenic disturbances of the pollinator environment of the short-lived Centaurium erythraea on mating patterns was investigated. First floral traits and the capacity for autonomous selfing were compared between two contrasting pollinator environments. In addition, transplantation experiments were combined with hand-pollination and emasculation treatments to assess the extent of pollen limitation and the contribution of autonomous selfing to total seed production in these pollinator environments.

3. Under severe pollinator impoverishment, C. erythraea produced fewer and smaller flowers that showed no herkogamy and strongly reduced P/O ratios. The capacity for autonomous selfing was 36·1% higher in these pollinator-limited environments than in more natural, pollinator-rich environments, where plants developed more, larger and markedly herkogamous flowers.

4. When assigned to the pollinator-rich environments, plants from pollinator-limited populations showed significantly higher outcross pollen limitation compared with the original plants. In contrast, plants from pollinator-rich environments assigned to pollinator-poor populations did not experience higher pollinator-mediated seed production and showed lower total seed production than plants originally occurring in these pollinator-limited environments.

5. These results demonstrate that human-induced pollen limitation selects for selfing as a means of reproductive assurance, whereas in the pollinator-rich environments, traits that support outcrossing are favoured.

1. The evolution of strategies of resource acquisition and allocation is often considered to be closely dependent on the degree of environmental variability. Within this framework, female insects that experience stochastic fluctuations in the availability of their egg-laying sites in time or space can be expected to be fully synovigenic (i.e. they start maturing eggs after a delay once reaching adulthood), which allows them to tailor their reproductive investment to variations in the resource. Proovigenic females (that have most of their eggs already mature at the onset of their adult life, which corresponds to a capital breeding strategy), on the contrary, should have an advantage when the availability of the egg-laying sites is predictable. There is, however, a dearth of empirical studies testing these predictions.

2. Here, we tested the hypothesis that four phytophagous insect species of the genus Curculio, which coexist on a strongly fluctuating resource that they exploit for egg-laying purposes, would all be synovigenic as strict proovigeny should be counterselected. The resource consisted of the acorns of oak trees Quercus spp. We conducted field surveys to determine the date of adult emergence in each weevil species and the ability of newly emerged females to produce eggs. We also analysed the stable isotope profile of wild-caught females as a proxy for their feeding activity. Finally, we tested females under laboratory conditions for their ability to produce mature eggs when not fed and investigated whether dietary intake influenced their longevity.

3. Taken together, our results show that, contrary to the usual predictions, the four weevil species that were all exposed to a markedly fluctuating environment exhibited sharply contrasting strategies of resource acquisition and allocation: three species were synovigenic, while the fourth was proovigenic. Unexpectedly, therefore, our findings show that a strict capital breeding species might not always be counterselected in a temporally stochastic environment. They further suggest that fluctuations in the environment should not promote a sole, optimal strategy of energy acquisition and allocation to reproduction but instead should favour their diversification.

1. One of the most exciting recent discoveries in the field of ecological immunology has been that insects employ the help of heritable symbionts as a defence against parasitoids and pathogens. Aphids commonly harbour the facultative bacterial endosymbiont Hamiltonella defensa, which is known to increase their resistance to parasitoids. It is unknown how this resistance develops during the aphids’ ontogeny, following the transmission bottleneck between mother and offspring, and how specific symbiont-conferred defences are.

2. We addressed these issues in the black bean aphid, Aphis fabae, by exposing aphids of different age classes to the parasitoid Lysiphlebus fabarum. The susceptibility of aphids that were either naturally or experimentally infected with H. defensa was compared with that of uninfected aphids.

3. Susceptibility to parasitoids decreased with aphid age, but aphids harbouring H. defensa showed an earlier and/or steeper decline to lower levels of susceptibility than aphids without this symbiont. This is consistent with the hypothesis that during aphid development, symbiont-conferred resistance builds up with bacterial population growth, which we documented using quantitative polymerase chain reaction (qPCR).

4. Parasitoids that successfully overcame the symbiont-conferred resistance still suffered from sublethal effects of H. defensa. They exhibited lower emergence, delayed development and reduced size compared with parasitoids developing in aphids without H. defensa.

5. The most striking result was a strong interaction on the rates of parasitism between aphid sublines infected with different isolates of H. defensa and the parasitoid lines they were exposed to, suggesting a high specificity of symbiont-conferred resistance.

6. Based on these results, we conclude that when faced with hosts possessing H. defensa, aphid parasitoids are under selection to preferentially attack the youngest host stages and/or to discriminate against symbiont-protected aphids. Furthermore, the specificity induced by H. defensa in the interaction between host and parasitoid is likely to have important consequences for co-evolution. It may result in negative frequency-dependent selection and thus promote genotypic variation.

1. Diving capacity generally increases with body size both within and among taxanomic groups because of the differential scaling between body oxygen stores and metabolic rate.

2. Despite being some of the largest animals of all time, rorqual whales exhibit very short dive times relative to other large divers because of the high energetic costs incurred during lunge feeding. This mode of filter feeding requires high drag for the engulfment of large volumes of prey-laden water, and the magnitude of both drag and engulfment volume is largely determined by the size and shape of the skull.

3. The positive allometry of rorqual skulls increases mass-specific engulfment capacity in larger whales, but the energetic requirements of feeding are also predicted to increase and thus further limit diving capacity.

4. To test the hypothesis that the energetic cost of a lunge is disproportionately higher in larger rorquals, we compared diving and lunge-feeding performance among three different-sized species (blue, fin and humpback whales) foraging on krill.

5. Our hydrodynamic analyses indicate that the mass-specific energy expenditure will increase with body size if rorquals lunge at length-specific speeds (in body lengths per second) that are independent of body size, a condition that is supported by tag data.

6. Although the absolute time required to filter each volume of water increased with body size, maximum dive duration and depth were not significantly different among species. As a consequence, the maximum number of lunges executed per dive decreased with body size.

7. These data suggest that, unlike all other true divers, adult rorqual species do not exhibit a positive relationship between body size and diving capacity. Larger rorquals forfeit diving capacity for greater engulfment capacity, a trade-off that favours the efficient exploitation of patchily dense prey aggregations. Such a trade-off may underlie different foraging strategies associated with resource partitioning, life history and ecological niche.

1. Age at maturity is hard to estimate for species that cannot be directly marked or observed throughout their lives and yet is a key demographic parameter that is needed to assess the conservation status of endangered species.

2. For loggerhead turtles (Caretta caretta) in the North Atlantic and North Pacific, juvenile growth rates (c. 10 cm year⁻¹) were calculated by examining size increases during transoceanic journeys; durations of which were estimated from satellite-tracked Lagrangian surface drifter buoy trajectories.

3. Lagrangian-derived growth estimates were used in a weighted loglinear model of size-specific growth rates for loggerhead turtles and combined with newly available information on size at maturity to estimate an age at maturity of 45 years (older than past estimates).

4. By examining the age at maturity for 79 reptile species, we show that loggerhead turtles, along with other large-bodied Testudine (turtle and tortoise) species, take longer to reach maturity than other reptile species of comparable sizes. This finding heightens concern over the future sustainability of turtle populations. By maturing at an old age, sea turtles will be less resilient to anthropogenic mortality than previously suspected.

1. Birds of marine environments have specialized glands to excrete salt, the saltglands. Located on the skull between the eyes, the size of these organs is expected to reflect their demand, which will vary with water turnover rates as a function of environmental (heat load, salinity of prey and drinking water) and organismal (energy demand, physiological state) factors. On the basis of inter- and intraspecific comparisons of saltgland mass (m_sg) in 29 species of shorebird (suborder Charadrii) from saline, fresh and mixed water habitats, we assessed the relative roles of organism and environment in determining measured m_sg species.

2. The allometric exponent, scaling dry m_sg to shorebird total body mass (m_b), was significantly higher for coastal marine species (0·88, N = 19) than for nonmarine species (0·43, N = 14). Within the marine species, those ingesting bivalves intact had significantly higher m_sg than species eating soft-bodied invertebrates, indicating that seawater contained within the shells added to the salt load.

3. In red knots (Calidris canutus), dry m_sg varied with monthly averaged ambient temperature in a U-shaped way, with the lowest mass at 12·5 °C. This probably reflects increased energy demand for thermoregulation at low temperatures and elevated respiratory water loss at high temperatures. In fuelling bar-tailed godwits (Limosa lapponica), dry m_sg was positively correlated with intestine mass, an indicator of relative food intake rates. These findings suggest once more that saltgland masses vary within species (and presumably individuals) in relation to salt load, that is a function of energy turnover (thermoregulation and fuelling) and evaporative water needs.

4. Our results support the notion that m_sg is strongly influenced by habitat salinity, and also by factors influencing salt load and demand for osmotically free water including ambient temperature, prey type and energy intake rates. Saltglands are evidently highly flexible organs. The small size of saltglands when demands are low suggests that any time costs of adjustment are lower than the costs of maintaining a larger size in this small but essential piece of metabolic machinery.

1. Acclimation or hardening to one stress in arthropods can lead to a plastic response, which confers increased resistance to other stresses. Such cross-resistance may indicate shared physiological resistance mechanisms and a possibility of joint evolution for resistance traits.

2. In this study, we tested for cross-resistance using Drosophila melanogaster as a model system. Adult females were assayed for resistance to cold, heat, desiccation and starvation following cold acclimation, heat hardening, desiccation hardening and starvation acclimation, resulting in 12 pretreatment-by-test combinations for estimating potential cross-resistance effects. The acclimation/hardening regimes were chosen so that flies enhanced their resistance to the same type of stress as that used for the particular pretreatment.

3. Two cases of cross-resistance were found, with desiccation-hardened and starvation-acclimated flies being more resistant than control ones in heat and desiccation resistance tests, respectively. In four cases, no acclimation/hardening effect was observed, and for six pretreatment-by-test combinations, the effect of acclimation/hardening was negative.

4. We also revealed that heat and desiccation hardening as well as acclimation to starvation had a cost under non-stressful conditions leading to reduced longevity. Cold acclimation did not affect longevity, although its effect was difficult to estimate precisely: during pretreatment at a low temperature, biological ageing of the flies might be delayed.

5. The pattern of acclimation/hardening responses considered in the context of literature data on stress resistance indicates that expression of heat-shock proteins is not likely to contribute to the observed cross-resistance, but other probable general stress resistance mechanisms such as reduction of metabolic rate and accumulation of energy reserves might be involved.

6. The lack of cross-resistance induced by acclimation/hardening treatments suggests that in an environment with multiple stresses, evolution of shared protective systems associated with plastic responses may be constrained.

1. Oxidative stress may provide a proximate link between investment in growth and/or reproduction and investment in self-maintenance. Dietary antioxidants, such as carotenoids and vitamin E, provide potentially important roles in regulating these trade-offs. Recent work suggests that carotenoids may have synergistic effects in combination with non-pigmentary antioxidants (e.g. vitamin E) on the expression of sexually selected traits in adulthood. However, these studies involved the supplementation of antioxidants to adults so did not take account of early life-history effects.

2. Here, we test the independent and combined roles of supplementation of carotenoids and vitamin E during early growth in regulating the expression of traits in adulthood, in ring-necked pheasants, Phasianus colchicus. Individuals supplemented with a combination of carotenoids and vitamin E were larger at adulthood than individuals receiving other treatment diets (including vitamin E or carotenoids alone), but there were no differences in ornament expression, immune function, the swelling response to phytohaemagglutinin or levels of oxidative damage.

3. This shows that there are synergistic early life-history effects of these dietary antioxidants on body size at adulthood and suggest that the allocation of limited antioxidant resources are prioritized towards traits that increase competitive ability rather than sexual attractiveness in this strongly sexually selected species.

1. The massive synchronized flowering and subsequent mortality of understorey bamboo species occur in infrequent and unpredictable intervals in temperate and subtropical forests around the world. Because of the sporadic occurrence of these flowering episodes and the long intervals between events, very little is known about their consequences on biogeochemical cycling in natural ecosystems.

2. In 2001, a synchronized flowering and dieback of the native bamboo, Chusquea culeou E. Desv., occurred, covering more than 200 000 ha in the north-west region of Patagonia, Argentina. We explored the impacts of this gregarious flowering event on litter decomposition and nitrogen turnover in an old-growth southern beech forest for 3 years after the flowering event.

3. Bamboo litter decomposed significantly slower than overstorey tree litter, and decomposition in flowered patches overall was significantly reduced compared to remnant live understorey patches. In addition, soil mineral nitrogen was reduced in flowered patches, and nitrogen transformations were altered, most notably in the third year after the flowering event.

4. This infrequent phenomenon of gregarious flowering could have consequences for carbon and nutrient cycling, as low-quality standing dead biomass is gradually incorporated into soil organic matter pools. This study demonstrates that large biotically mediated perturbations of understorey vegetation can impact biogeochemical cycles in temperate forest ecosystems by reducing carbon turnover and altering nitrogen availability and transformations, even in the absence of physical disturbance.

1.Because of its mechanical properties, wood density may affect the way that trees expand their stem and crown to exploit favourable light conditions in a mechanically stable way. From engineering theory and wood density properties, it is predicted that in terms of biomass investment, low-density wood is more efficient for vertical stem expansion, while high-density wood is more efficient for horizontal branch expansion. So far, these predictions have rarely been tested by empirical studies.

2.We tested these predictions for 145 co-occurring tree species in a Malaysian tropical rainforest. For each species, we selected trees across a broad size range and measured architectural dimensions (stem diameter, height of the lowest foliage and crown width). We used a hierarchical Bayesian model to estimate species-specific allometric relationships between architectural dimensions including estimated stem biomass. Then, we examined correlations between species wood density and estimated architectural variables at standardized heights.

3.When species were compared at standardized tree heights, wood density correlated negatively with stem diameter and positively with stem biomass at most reference heights. This indicates that species with low wood density produce thicker stems but at lower biomass costs. Wood density correlated positively with crown width and negatively with height of the lowest foliage, which indicates that high wood density species have wider and deeper crowns than low wood density species. These relationships were maintained at most reference heights. However, the relationship with crown width was nonsignificant above 18 m height. This may reflect large plastic response of lateral crown expansion to a local condition.

4. Wood density explains the trade-off between effective vertical stem expansion and horizontal crown expansion across co-occurring tropical tree species. Such mechanical constraints characterize the difference in tree architecture between low wood density species that show an efficient height expansion to attain better light conditions in the exposed canopy and high wood density species that show an efficient horizontal crown expansion to enhance current light interception and persistence in the shaded forest understorey. Our study thus suggests that the mechanical constraints set by wood density contribute to the co-existence of species differing in architecture and light capture strategy.

1. The natural enemy hypothesis (NEH) predicts that alien plant species might receive less pressure from natural enemies than do related coexisting native plants. However, most studies to date are based on pairs of native and alien species, and the results remain inconclusive. The level of attack by native generalist herbivores can vary considerably between plant species, depending on defensive traits and strategies. Plant defences include preformed constitutive and induced defences that are activated as plastic responses to herbivore attack. However, the efficacy of induced defences could be altered when alien species entering an area are exposed to native enemies.

2. We tested the NEH for several closely related alien and native pines to Europe by examining early anti-herbivore resistance to damage by two generalist native insect herbivores (Hylobius abietis and Thaumetopoea pityocampa); the differences in constitutive and inducible chemical defences (i.e. non-volatile resin and total phenolics in the stem and needles); and whether consumption preferences shift after induced defences have been triggered by real herbivory.

3. We did not find alien pines to be less damaged by two generalist herbivores than native pines were. The constitutive concentration of chemical defences significantly differed among pine species. The concentration of constitutive total phenolics in the stem was greater in native than in alien pines. The opposite trend was found for constitutive total phenolics in the needles. The concentration of chemical defences (non-volatile resin and total phenolics) in the stem significantly increased after herbivory by H. abietis. Moreover, the induction of total phenolics by H. abietis damage was significantly greater in native pine species than in alien pines. On the other hand, only concentrations of non-volatile resin in needles significantly increased after herbivory by T. pityocampa, but without significant differences in inducibility between alien and native pines. In cafeteria bioassays, H. abietis consumed the twigs from alien more than those from native species irrespective of prior exposure to the insect. Meanwhile, no differences among range origin were found in the T. pityocampa cafeteria bioassays.

4. Overall, we found no support for the NEH in alien pines to Europe. This suggests that alien pines, in regions where they coexist with native congeners, may be controlled by native generalist herbivores, this being one reason that invasion by alien pines is not frequent in Europe.

1. Constraints of resource allocation between reproduction and adult survival have been implicated in much life-history variation, yet physiological or functional trade-offs with juvenile survival may be just as important. Here, we examined selection on a juvenile trait that is a key determinant of semelparous (monocarpic) vs. iteroparous (polycarpic) life-history expression.

2. In Erysimum capitatum, iteroparous plants produce more rosettes at the juvenile stage than do semelparous plants; those rosettes perennate, enabling subsequent reproductive episodes. Thus, the number of rosettes produced before reproduction is a strong determinant of iteroparity. We tested whether increased rosette production compromised juvenile survival under conditions similar to those in which semelparity predominates over iteroparity.

3. Using plants from six natural populations, we tested the association between rosette production and juvenile survival under drought conditions typical of the field sites of semelparous E. capitatum populations. We also manipulated rosette number by physically removing rosettes and examined the effect of rosette removal on drought resistance.

4. Under drought conditions, plants with fewer rosettes had higher survival, and the physical excision of rosettes improved survival (significantly or marginally) under drought stress in five of six natural populations.

5. The lower production of rosettes, typical of semelparous E. capitatum, was associated with increased juvenile survival under drought stress. The results suggest adaptive differentiation of rosette production, at least partially in response to drought stress. Given the role of apical dominance in multiple rosette development, natural selection seems to favour stronger apical dominance under drought conditions. Drought stress is predicted to be more common at high elevation as a result of climate change, and the novel drought stress could increase juvenile mortality of alpine E. capitatum. Because rosette production at the juvenile stage is necessary for iteroparity, these results demonstrate that drought-induced selection on traits that determine early survival has significant potential to influence the evolution of adult life-history expression.