Catalogue of Organisms

Brachythecium salebrosum: Some Like It Temperate

noreply@blogger.com (Christopher Taylor) — Tue, 24 Jan 2012 05:09:00 +0000

Brachythecium salebrosum, photographed in Slovakia by M. Lüth.

Brachythecium salebrosum is a species of moss found in many temperate regions of the world. It often grows in drier habitats than other mosses; in a study of the effects of human disturbance on forest moss communities in Estonia, B. salebrosum made up slightly less than a tenth of the moss flora in unmanaged forests, but accounted for more than a quarter of the flora in managed forests (Vellak & Paal 1999). Brachythecium salebrosum is known from Eurasia, North America, southernmost Africa and Australasia. Interestingly, it hasn't yet been recorded from South America (Delgadillo 1993), and an explanation for its distribution would need to explain how it came to disperse (or vicariate) between North America and South Africa yet bypass South America and northern Africa. Another oddity in its distribution can be seen in comparison to the similar species Brachythecium rotaeanum: while both species are found in Eurasia and North America, B. salebrosum is more common in the western part of each continent while B. rotaeanum dominates in the east (so as one travels east from Europe, the distribution bands are salebrosum-rotaeanum-salebrosum-rotaeanum) (Ignatov et al. 2008). Some authors (particularly European ones) have expressed scepticism about the distinction between these two species, but they are distinguished by both morphological and molecular characters according to Ignatov et al. (2008).

Individual leaf of Brachythecium salebrosum, photographed by Russ Kleinman & Karen Blisard.

Distinguishing Brachythecium salebrosum from related species is, admittedly, not a simple task. Specimens of this species can vary quite significantly across their range. Generally, however, B. salebrosum has plicate leaves (i.e. they are folded longitudinally like an accordion) that are more or less falcate in shape with serrated margins. There is a clearly distinct group of small subquadrate cells at the lower corners of the leaf. The spore capsules are held more or less horizontally, and the seta supporting the capsule is generally about two centimetres high (Ignatov et al. 2008).

REFERENCES

Delgadillo M., C. 1993. The Neotropical-African moss disjunction. The Bryologist 96 (4): 604-615.

Ignatov, M. S., I. A. Milyutina & V. K. Bobrova. 2008. Problematic groups of Brachythecium and Eurhynchiastrum (Brachytheciaceae, Bryophyta) and taxonomic solutions suggested by nrITS sequences. Arctoa 17: 113-138.

Vellak, K., & J. Paal. 1999. Diversity of bryophyte vegetation in some forest types in Estonia: a comparison of old unmanaged and managed forests. Biodiversity and Conservation 8: 1595-1620.

The Ornithocheirids: Misunderstood Giants

noreply@blogger.com (Christopher Taylor) — Tue, 17 Jan 2012 09:24:00 +0000

The original specimen of Ornithocheirus simus, from Joseph Dinkel.

The pterosaurs of the Ornithocheiridae that lived between the Early and mid-Cretaceous were not the largest pterosaurs to ever live, but with a possible maximum known wingspan of about 7 m (Martill & Unwin 2011) they were certainly big enough (for comparison, an Australian pelican has a wingspan of about 2.5 metres). Ornithocheirids have been recorded from numerous parts of the world—Europe, South America, Africa and China—and, like the large seabirds that are perhaps their closest modern analogues (where 'closest' is a relative term), were probably found worldwide.

Reconstruction of Ornithocheirus mesembrinus, by Dmitry Bogdanov.

The 'misunderstood' in the title to this post refers specifically to the type genus, Ornithocheirus, which has suffered something of an identity crisis over the years. In the 1800s, 'Ornithocheirus' was used as a catch-all genus for almost all Cretaceous European pterosaurs, many known from only fragmentary remains. Eventually, the name came to be associated with a number of species centred around the British O. compressirostris. However, Unwin (2001) pointed out that, at its earliest publication, only one valid species was associated with Ornithocheirus, O. simus, and that species automatically becomes the type of the genus. Ornithocheirus simus is not currently regarded as congeneric with 'O.' compressirostris (and had for many years been treated under the name of Criorhynchus, e.g. Wellnhofer 1991), and so most species previously treated as Ornithocheirus are now treated as a genus Lonchodectes, and not ornithocheirids. Just to confuse matters further, however, some recent authors have continued to treat Ornithocheirus as typified by O. compressirostris, and refer to the 'Ornithocheiridae' of Unwin (2001) as the 'Anhangueridae'. On the other hand, some recent phylogenies have even suggested that Lonchodectes may itself be related to the Ornithocheiridae (e.g. Andres & Ji 2008).

Reconstruction of Coloborhynchus piscator, by Joseph Conway.

Ornithocheirus simus was originally described from a piece of the front of the rostrum found in the Cambridge Greensand of England. This piece was notably deep, and so O. simus was reconstructed as having a short, deep puffin-like skull. It wasn't until the later discovery of a more complete skull in a closely-related South American species, Ornithocheirus mesembrinus (alternatively known as Tropeognathus mesembrinus), that a more accurate reconstruction was possible: Ornithocheirus species had a long rostrum, similar to that found in related pterosaurs, but with prominent rounded dorsal and ventral crests at the distal end. Species of another ornithocheirid genus, Anhanguera (also known from England and South America), had rostral crests set further back and differently shaped. These crests most likely served some form of display function; suggestions that they may have aided in the capture of fish on the wing by easing the rostrum's passage through the water (Wellnhofer 1991) seem unlikely, as other ornithocheirid genera, such as Brasileodactylus and Barbosania, lacked rostral crests entirely (Elgin & Frey 2011). The possibility has been raised that some crested and crestless forms may represent different sexes of the same species, but unfortunately the fossil record of ornithocheirids may not be extensive enough to establish whether this is the case.

The skull of Ludodactylus piscator, via Darren Naish.

The phylogeny of pterosaurs remains a contentious issue but most studies have agreed that ornithocheirids form part of a clade that also includes the Istiodactylidae, Pteranodontidae and Nyctosaurus (though how exactly these taxa are interrelated has not been agreed upon). Ornithocheirids are distinguished from related forms by the arrangement of their teeth, with the first three pairs enlarged to form a terminal rosette. Most ornithocheirids are also distinguished from Pteranodontidae and Nyctosaurus by the absence of a crest on the back of the head. A noteworthy exception is Ludodactylus sibbicki, described by Frey et al. (2003) from a skull possessing a crest at least basally like that of Pteranodon (the skull is preserved on a slab of rock prepared commercially, and the distal portion of the crest [if it had been present] was removed when the slab was cut). However, it is worth noting that Ludodactylus has not (to my knowledge) been included in a formal phylogenetic analysis. Ludodactylus was identified as an ornithocheirid due to its tooth morphology, but the absence of teeth in Pteranodontidae and Nyctosaurus makes them incomparable in this regard. As the Istiodactylidae (with their broad, duck-like rostra) are also reasonably autapomorphic in their skull morphology, I can't help wondering whether the supposed ornithocheirid characters might be plesiomorphic for the larger pteranodontoid clade. But that, of course, is pure speculation on my part, and something only further study could establish.

REFERENCES

Andres, B., & Ji Q. 2008. A new pterosaur from the Liaoning Province of China, the phylogeny of the Pterodactyloidea, and convergence in their cervical vertebrae. Palaeontology 51 (2): 453-469.

Elgin, R. A., & E. Frey. 2011. A new ornithocheirid, Barbosania gracilirostris gen. et sp. nov. (Pterosauria, Pterodactyloidea) from the Santana Formation (Cretaceous) of NE Brazil. Swiss Journal of Palaeontology 130: 259-275.

Frey, E., D. M. Martill & M.-C. Buchy. 2003. A new crested ornithocheirid from the Lower Cretaceous of northeastern Brazil and the unusual death of an unusual pterosaur. In Evolution and Palaeobiology of Pterosaurs (E. Buffetaut & J.-M. Mazin, eds) Geological Society Special Publications 217: 55-63. The Geological Society: London.

Martill, D. M., & D. M. Unwin. 2011. The world’s largest toothed pterosaur, NHMUK R481, an incomplete rostrum of Coloborhynchus capito (Seeley, 1870) from the Cambridge Greensand of England. Cretaceous Research 34: 1-9.

Unwin, D. M. 2001. An overview of the pterosaur assemblage from the Cambridge Greensand (Cretaceous) of Eastern England. Mitt. Mus. Nat.kd. Berl., Geowiss. Reihe 4: 189-221.

Wellnhofer, P. 1991. The Illustrated Encyclopedia of Pterosaurs. Salamander Books: London (reprinted 2000, in The Illustrated Encyclopedia of Dinosaurs (D. Norman & P. Wellnhofer). Salamander Books).

Callocystitids: Ambulacra Advancement and Rhomb Reduction

noreply@blogger.com (Christopher Taylor) — Tue, 10 Jan 2012 05:43:00 +0000

The Upper Silurian callocystitid Staurocystis quadrifasciata, from Museum Victoria.

The Palaeozoic echinoderms included many distinctive groups that have no close relatives among the modern fauna: blastoids, cornutes, solutes, ctenocystoids... to name just a few. From the Ordovician to the Devonian, this diverse fauna also included a hodge-podge assemblage known as cystoids. Cystoids are a grouping of mostly stalked echinoderms in which certain plates in the theca are perforated by regular arrangements of pores that probably functioned in respiration. Cystoids were not always regularly pentamerous like other echinoderms, and some were notably asymmetrical. The ambulacra were recumbent on the theca, and the feeding appendages were brachioles rather than arms (for the difference between brachioles found in many fossil echinoderms and arms found in crinoids, see the post on blastoids). Cystoids would have been filter-feeders and were probably largely sedentary. Cystoids include some very disparate forms, and many researchers have suggested that they may represent a polyphyletic assemblage. Various authors have suggested cystoid ancestry for other echinoderm groups, such as blastoids or crinoids, but this remains controversial.

The Upper Silurian Schizocystis armata, from Kesling (1967). The two pore rhombs of this species are visible just above the center and at the lower right of the theca.

The Callocystitidae were a family of cystoids that persisted over most of the total cystoid time range. Callocystitids belonged to the major cystoid subgroup called the Rhombifera, in which the diagnostic pore groups were arranged as paired assemblies, commonly called pore rhombs, that spanned the border between two thecal plates (as opposed to the remaining cystoids, the Diploporita, in which pore assemblies each occupied a single plate). Broadhead & Strimple (1978) diagnosed the Callocystitidae based on the arrangement and position of the pore rhombs, together with their possession of a relatively small periproct (the circle of plates that indicates the position of the anus) and the number of radial plates in the theca. All callocystitids possessed a stalk, often divided into a flexible proximal section and a more rigid distal section. Broadhead & Strimple (1978) recognised four subfamilies of callosystitids, but one of these, the Apiocystitinae was explicitly suggested to be paraphyletic to the Callocystitinae and Staurocystinae. This was supported by the numerical phylogenetic analysis of Sumrall & Brett (2002), who furthermore suggested that the Callocystitinae was polyphyletic.

Theca of the Upper Silurian apiocystitine Lovenicystis angelini, from Kesling (1967).

The fourth of Broadhead & Strimple's subfamilies, the Scoliocystinae, was suggested to lie outside the clade formed by the other three; Sumrall & Brett's analysis only included Scoliocystis, but does not contradict this. Scoliocystines have the ambulacra relatively short, restricted to the summit of the theca, and would have had only a small number of brachioles. The most extreme example was the Lower Silurian Osculocystis, which had only a single extremely long brachiole (Paul & Donovan 2011). Another scoliocystine, Schizocystis, had one side of the theca relatively flat and the pore rhombs reduced in number and restricted to the other side, and may have lain on its side in life rather than standing upright.

Reconstruction of Pseudocrinites together with a number of individuals of the discosorid Phragmoceras by Alison Carey.

The remaining three subfamilies had more extensive ambulacra, extending right down to the base of the theca in some species. Apiocystitines and callocystitines had four or five ambulacra, usually branched in callocystitines and unbranched in apiocystitines, that did not strongly protrude above the surface of the theca and had widely spaced brachioles. The more distinctive Staurocystinae had two to four stongly protruding ambulacra that carried tightly packed brachioles. In the staurocystine Pseudocrinites, the theca was discus-shaped with its two ambulacra running around the outer rim of the disc (Kesling 1967).

REFERENCES

Broadhead, T. W., & H. L. Strimple. 1978. Systematics and distribution of the Callocystitidae (Echinodermata, Rhombifera). Journal of Paleontology 52 (1): 164-177.

Kesling, R. V. 1967. Cystoids. In Treatise on Invertebrate Paleontology pt. S. Echinodermata 1. General characters. Homalozoa-Crinozoa (except Crinoidea) (R. C. Moore, ed.) vol. 1 pp. S85-S267. The Geological Society of America, Inc., and The University of Kansas: Lawrence (Kansas).

Paul, C. R. C., & S. K. Donovan. 2011. A review of the British Silurian cystoids. Geological Journal 46: 434-450.

Sumrall, C. D., & C. E. Brett. 2002. A revision of Novacystis hawkesi Paul and Bolton 1991 (Middle Silurian: Glyptocystitida, Echinodermata) and the phylogeny of early callocystitids. Journal of Paleontology 76 (4): 733-740.

The Gagrella Problem Cranked Up to Eleven

noreply@blogger.com (Christopher Taylor) — Fri, 06 Jan 2012 06:27:00 +0000

A Leiobunum eating a cricket, photographed in North Carolina by Jeffrey Pippen.

In previous posts on this site, I have referred to the problem of Gagrella: a large genus of Asian harvestmen diagnosed on the basis of characters long since recognised as unreliable that remains unrevised because no-one has yet been in a position to take on the amount of work required. Well, a paper has come out in the last few weeks that indicates that the Gagrella issue is just part of a larger problem, one of truly demonic proportions.

The British Nelima gothica, photographed by Gordon.

Gagrella belongs to a family of harvestmen called the Sclerosomatidae. Sclerosomatids are distinguished by having a more heavily sclerotised dorsum than most other long-legged harvestmen, and by the morphology of the male genitalia, with many (but not all) species having lateral extensions (like wings) on the shaft just behind the glans. Within the Sclerosomatidae, most authors have recognised four subfamilies: Sclerosomatinae, Gagrellinae, Leiobuninae and Gyinae. The boundaries between the subfamilies have long been realised to be a bit fuzzy, particularly between the Leiobuninae and Gagrellinae. A few molecular studies (for instance, Giribet et al. 2010) that have included more than one representative of more than one subfamily have failed to resolve them as separate. Nevertheless, the subfamilies have served as a convenient way to divide what is a quite large family of over 1200 described species, at least until a more extensive analysis can be conducted.

Enter Hedin et al. (2012) who take molecular data for six genes from seventy-odd sclerosomatids, mostly of the Holarctic genera Leiobunum and Nelima (both Leiobuninae). One suspects that the primary focus of the authors was originally just the phylogeny of these two genera, with the smattering of other sclerosomatids in the mix primarily intended as outgroups. But then they got a result that looks like this (click on the image for a higher resolution):

Yikes. That is a mess. The two main genera have not only failed to resolve as monophyletic, they have completely exploded. Gyas (the type species of the Gyinae) has apparently been so terrified by this show of opilionid pyrotechnics that it has scurried off to join the Phalangiidae. The Gagrellinae have also undergone something of a breakdown, appearing in four separate places on the tree (two of those including species supposedly of a single genus). But this is not simply a matter of poor resolution: many of the incongruent clades are reasonably supported. It is also worth noting that the results are not inconsistent with those recovered by Giribet et al. (2010) who included seven sclerosomatid species in their analysis.

As noted by the authors, the distribution of taxa in the results is not entirely random. There is a certain amount of biogeographic patterning, with the European and Japanese taxa included forming distinct clades, while the New World taxa form three clades. Within the Japanese taxa (which are some of the best studied sclerosomatids), there is some correlation with species groups recognised on morphological grounds, such as monophyly of the Leiobunum curvipalpe group. This latter example is interesting, as it represents a group of species that exhibit conservative features of external morphology despite showing broad variation in genitalic characters (Tsurusaki 1985).

The sclerosomatine Astrobunus laevipes, photographed by Ch. Komposch.

Draining the morass of sclerosomatid taxonomy and phylogeny will doubtless be an arduous process, with all the large genera currently recognised likely to be polyphyletic. The support by Hedin et al. for previously recognised groups such as the Leiobunum curvipalpe complex suggest that morphological features will not be irrelevant in revising the family, but they will have to be analysed in their proper context. For instance, Hedin et al. suggest that the recovered polyphyly of Nelima may indicate that this genus, primarily defined by the absence of ornamentation found in other genera, may represent convergence through paedomorphosis (the acquisition of sexual maturity in a juvenile stage of development). In particular, this could explain how Giribet et al. (2009) found Nelima silvatica nested within two species of Sclerosomatinae, a primarily Mediterranean group of flattened, particularly heavily sclerotised species that might have been thought better supported than the other sclerosomatid subfamilies (unfortunately, Hedin et al.'s analysis includes only a single sclerosomatine). The view of the road ahead might be daunting, but it promises to be a memorable journey.

REFERENCES

Giribet, G., L. Vogt, A. Pérez González, P. Sharma & A. B. Kury. 2010. A multilocus approach to harvestman (Arachnida: Opiliones) phylogeny with emphasis on biogeography and the systematics of Laniatores. Cladistics 25: 1-30.

Hedin, M., N. Tsurusaki, R. Macías-Ordóñez & J. W. Shultz. 2012. Molecular systematics of sclerosomatid harvestmen (Opiliones, Phalangioidea, Sclerosomatidae): geography is better than taxonomy in predicting phylogeny. Molecular Phylogenetics and Evolution 62: 224-236.

Tsurusaki, N. 1985. Taxonomic revision of the Leiobunum curvipalpe-group (Arachnida, Opiliones, Phalangiidae). I. hikocola-, hiasai-, kohyai-, and platypenis-subgroups. Journal of the Faculty of Science of the Hokkaido University VI, Zoology 24: 1-42.

Marginal Limpets

noreply@blogger.com (Christopher Taylor) — Mon, 02 Jan 2012 07:31:00 +0000

Shells of Emarginula solidula, photographed by Jan Delsing.

For today's subject taxon, I've drawn the Emarginulini. This is a tribe within the gastropod family Fissurellidae, members of which are commonly known as keyhole or slit limpets. They get these names because of openings in their shells: keyhole limpets have a distinct hole at the apex of their shell, while slit limpets have a longitudinal slit running back from the front of their shell. In both groups, the slit or 'keyhole' functions in excretion. Gastropods undergo a process early in development known as torsion: the viscera of the embryo twists around so that it reverses its original direction (you can see a basic diagram of the process here). The reasons why this happens remain somewhat uncertain (one early suggestion was that it is what allowed the larval gastropod to retract into its shell and close the shell opening with an operculum) but a potentially negative side-effect of the process is that the anus comes to open directly above the mouth. Unless you want to go through your life with a bit of a funny taste in your mouth, this is not ideal. Therefore, many torted gastropods develop some sort of sinus or recess in their shell so the anal opening can be moved rearwards, away from the mouth.

Live individual of Tugali parmophoroidea, from here. Tugali has an expanded mantle, but is still able to retract it body underneath the shell for protection.

The members of the Emarginulini as recognised by Bouchet et al. (2005) are slit limpets rather than keyhole limpets, though in some species the slit has become much reduced and may only be visible on the underside of the shell (i.e there is a ventral groove rather than a full slit). Bouchet et al. (2005) divided the Fissurellidae between the Fissurellinae and Emarginulinae, a classification based on the structure of the radula and shell muscles (Aktipis et al. 2011). The Fissurellinae are all keyhole limpets, but Bouchet et al.'s Emarginulinae included (in addition to the Emarginulini) the tribe Diodorini, whose members are keyhole limpets like the Fissurellinae but have emarginuline internal anatomy. Other authors have recognised this group as a third intermediate subfamily. Two further tribes of Emarginulinae, the Scutini and Fissurellideini, include species with expanded mantles and reduced shells that may be entirely concealed within the soft body of the slug-like animal.

An elephant snail or shield limpet Scutus sp., from here. This genus has a greatly enlarged mantle, which usually folds over to conceal the reduced shell.

However, this classification of the fissurellids was challenged by the molecular analysis of Aktipis et al. (2011). The results of these authors indicated that the Emarginulini of Bouchet et al. (2005) is para- or polyphyletic. A clade of Fissurellinae with Diodorini indicates a single origin of keyhole limpets, with the emarginuline radula and muscle structure being ancestral for fissurellids as a whole. This result is also consistent with the fossil record: 'emarginulines' are known as early as the Triassic, but fissurellines and diodorines have not been found earlier than the Caenozoic. Aktipis et al. (2011) therefore recognised a more restricted monophyletic Emarginulinae containing the genera Emarginula, Montfortula, Tugali and Scutus, while more basal forms (sister to all other fissurellids) were separated as the Hemitominae (Aktipis et al. did not analyse the position of the Fissurellideini). Of Aktipis et al.'s Emarginulinae proper, only Emarginula has a well-developed slit (the others have ventral shell grooves; Scutus has a quite reduced shell), but this genus was also not monophyletic. Instead of aligning by morphology, the species analysed formed clusters corresponding more to their biogeography: a Mediterranean Emarginula clade, a Pacific clade of Emarginula and Montfortula species, and an Australian clade of Scutus and Tugali. The relationships between these three clades varied by analysis method. The Australian Scutus clade was not necessarily sister to the remaining Emarginulinae, so it may not be worthwhile at this point in time distinguishing the tribes Emarginulini and Scutini.

REFERENCES

Aktipis, S. W., E. Boehm & G. Giribet. 2010. Another step towards understanding the slit-limpets (Fissurellidae, Fissurelloidea, Vetigastropoda, Gastropoda): a combined five-gene molecular phylogeny. Zoologica Scripta 40 (3): 238-259.

Bouchet, P., J.-P. Rocroi, J. Frýda, B. Hausdorf, W. Ponder, Á. Valdés & A. Warén. 2005. Classification and nomenclator of gastropod families. Malacologia 47 (1-2): 1-397.

Ormyrids: Attacking the Gall

noreply@blogger.com (Christopher Taylor) — Wed, 28 Dec 2011 05:34:00 +0000

Female of Ormyrus nitidulus, photographed by Penny Metal.

Everyone knows about God's supposed inordinate fondness for beetles, but it is my opinion that the true poster children for insect diversity should be the wasps. Wasps, admittedly, do not have as many described species as beetles (there are some who suspect that the actual number of species of wasp may eventually be higher, but that remains in the realm of the hypothetical). However, many species of beetle are very difficult to distinguish except by skilled specialists, being otherwise small, brown, and conservative. Wasps, on the other hand, come in a kaleidoscopic array of colours and shapes, such that even a novice may look at an array of wasps (see the top of this post, for instance) and be immediately struck by the disparity.

An unnamed species of Ormyrus, photographed by Simon van Noort.

The Chalcidoidea, commonly referred to as chalcids, are one of the largest subgroups of wasps, a clade of mostly small (often minute), mostly parasitoid wasps (some have larvae that feed on plants). Members of the Ormyridae, one of the commonly recognised families of chalcids, are generally about two to three millimetres long. Ormyrids are distinguished from other chalcids by their robust body form, with a strongly sclerotised gaster* (ormyrids and perilampids tend to look like steroid-abusing pteromalids). The segments of the gaster are usually ornamented by rows of coarse foveae (pits) that give it a distinctive rough appearance, though in some species these foveae are less obvious or are replaced by longitudinal ribs (Bouček 1988). Ormyrids are often recorded in association with plant galls, but are not gall-formers themselves: rather, they are parasites of the insect larvae that formed the galls (usually flies or other wasps). Some ormyrids are associated with figs and parasites of fig wasps.

*Wasp researchers generally refer to the sections of the body behind the head by terms such as 'mesosoma' and 'gaster' (or metasoma), rather than 'thorax' and 'abdomen'. This is because the section of the body that is the first segment of the abdomen in other insects has become the last segment of the mesosoma in Hymenoptera.

A female of Ormyrus on a knopper gall (a type of gall that develops when a developing acorn of the pedunculate oak Quercus robur is parasitised by the cynipid wasp Andricus quercuscalicis), photographed by Tristram Brelstaff.

There are about 125 known species of ormyrid (making this a quite small family by chalcid standards) according to the Universal Chalcidoidea Database (an absolutely wonderful resource). However, there isn't yet a really good classification system within the family. Ormyrids vary to a fair degree, particularly in the form of the antennae or the ornamentation of the gaster, but most authors have placed almost all species within the single genus Ormyrus. Attempts to subdivide this diverse group (for instance, that of Doğanlar, 1991, who recognised four genera of ormyrids with three subgenera within Cyrtosoma) have suffered from not considering the full range of ormyrid diversity. Some of the Australian forms referred to by Bouček (1988), for instance, may not be placeable in Doğanlar's system. Until an appropriately large-scale review is conducted, most authors will probably continue to recognise an all-purpose Ormyrus.

REFERENCES

Bouček, Z. 1988. Australasian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International: Wallingford (UK).

Doğanlar, M. 1991. Systematic positions of some taxa in Ormyridae and descriptions of a new species of Ormyrus from Turkey and a new genus in the family (Hymenoptera, Chalcidoidea). Türkiye Entomoloji Dergisi 15 (1): 1-13.

An Introduction to Malaconothrus

noreply@blogger.com (Christopher Taylor) — Tue, 20 Dec 2011 06:58:00 +0000

Specimen of Malaconothrus monodactylus, from the Biodiversity Institute of Ontario (M. mollisetosus was listed as a synonym of M. monodactylus by Subías 2004).

Malaconothrus is a genus of about sixty species of oribatid mites found almost worldwide. The only continent from which Malaconothrus species have not yet been recorded is Antarctica, though M. translamellatus is known from Île Amsterdam in the subantarctic Indian Ocean (Subías 2004). Malaconothrus species specialise in damp habitats, often found among moss or in marshes. They are small yellowish mites, often covered with an ornamented cerotegument (a thick waxy cuticle) (Luxton 1987). They are also parthenogenetic, with females laying unfertilised eggs that hatch into more females.

Schematic drawing of Malaconothrus monodactylus (minus legs) from Luxton (1987).

Malaconothrus belongs to a group of oribatids called the Crotonioidea (often also referred to as nothroids). Because crotonioids are long-lived, slow-breeding and poor dispersers, they have received a certain amount of attention as potential indicators of environment health. In the context of the post linked to above, crotonioids are part of the Desmonomata, so outside the large oribatid clade of the Circumdehiscentiae or Brachypylina*. They have broad genital and anal plates that take up the greater part of the underside behind the legs (Balogh & Balogh 1992). Malaconothrus and its most closely related genus, Trimalaconothrus, differ from other crotonioids in having a band of soft cuticle across the underside between the levels of the second and third legs, i. e. they are dichoid rather than holoid (Norton 2001). They also lack bothridia, specialised enlarged sensory setae that are present at the rear of the prodorsum in the majority of oribatids. Malaconothrus and Trimalaconothrus are distinguished from each other by Malaconothrus having one claw at the end of each leg, while Trimalaconothrus has three. Subías (2004) divided Malaconothrus between two subgenera: in Cristonothrus, the dorsum is divided by a pair of longitudinal ridges, but in Malaconothrus sensu stricto there are no dorsal ridges.

*For some reason, oribatids seem to suffer something of an embarrassment of higher taxon names.

Dorsal and ventral view of Malaconothrus rohri from Balogh (1997). Note the pattern of ridges on the dorsum characteristic of Cristonothrus.

Malaconothrus has suffered a certain degree of confusion about its type status (Luxton 1987). When he first established Malaconothrus in 1904 (as a subgenus of Lohmannia), Berlese only listed one name in explicit combination, Lohmannia (Malaconothrus) egregia. However, in his discussion of this species, Berlese compared it to the pre-existing Nothrus monodactylus in a manner that implied the latter should also be included in his new subgenus. Subsequent authors have disagreed over whether L. egregia or N. monodactylus should be regarded as the type species of Malaconothrus, though more recent authors have settled on the latter.

REFERENCES

Balogh, J. & P. Balogh. 1992. The Oribatid Mites Genera of the World vol. 1. Hungarian Natural History Museum: Budapest.

Balogh, P. 1997. New species of oribatids (Acari) from the neotropical region. Opusc. Zool. Budapest 29-30: 21-30.

Luxton, M. 1987. Mites of the genus Malaconothrus (Acari: Cryptostigmata) from the British Isles. Journal of Natural History 21 (1): 199-206.

Subías, L. S. 2004. Listado sistemático, sinonímico y biogeográfico de los ácaros oribátidos (Acariformes, Oribatida) del mundo (1758-2002). Graellsia 60 (número extraordinario): 3-305.

The State of Peridinium

noreply@blogger.com (Christopher Taylor) — Mon, 12 Dec 2011 06:04:00 +0000

As I've said on many an occasion before, dinoflagellates are complicated. Obscenely complicated. So when my search for a random post topic brought up the dinoflagellate genus Peridinium, I approached it with a certain amount of dread. If you're not familiar with dinoflagellates, the diagram at the top of this post will explain a lot of the terminology I'm about to use.

Specimen of Peridinium cf. cinctum, photographed by Kate Howell. Peridinium cinctum is the type species of Peridinium.

Peridinium is a genus that has been used in the past to cover a wide range of freshwater and marine dinoflagellates. For a long time, the standard diagnosis of Peridinium was that it contained species with four apical plates (the ring of plates at the front of the cell when it is moving), seven precingular plates (the ring of plates in front of the cingulum), five postcingular plates and two antapical plates (Carty 2008). However, the genus has been divided by differences in the shape and arrangements of the plates making up the theca into a number of species groups, and more recent studies have concurred that these species groups are not all closely related to each other. While support remains low in most phylogenetic studies of dinoflagellates, and many species remain to be analysed, indications are that all of the marine species and many of the freshwater species are not true Peridinium (Horiguchi & Takano 2006; Logares et al. 2007). As it currently stands, the probably monophyletic Peridinium sensu stricto includes two species groups, the P. cinctum and P. willei groups, and is exclusively freshwater. As well as the characters mentioned above, true Peridinium species have three apical intercalary plates between the apical and precingular plates, five cingular plates, and ridges on all the plates forming an areolate pattern. They are also united by a distinct combination of which plates in the front section of the organism break off when the theca is shed during cell division (Craveiro et al. 2009). The two species groups differ in the exact arrangement of the plates anterior to the cingulum: in the P. willei group they are symmetrical relative to the dorsal-ventral axis, vs asymmetrical in the P. cinctum group. Slightly surprisingly, though the presence or absence of an apical pore was one of the first characters used to subdivide the genus Peridinium, Peridinium sensu stricto includes both species with (such as P. bipes) and without (such as P. cinctum and P. willei).

SEM image of Peridinium gatunense, by Pawel Owsiany.

Peridinium species are photosynthetic, with a much-lobed chloroplast that ramifies through the cell. One species, identified by Hickel & Pollingher (1988) as P. gatunense, has been intensely studied as the creator of annual blooms in Lake Kinneret in Israel.

REFERENCES

Carty, S. 2008. Parvodinium gen. nov. for the Umbonatum Group of Peridinium (Dinophyceae). Ohio Journal of Science 108 (5): 103-107.

Craveiro, S. C., A. J. Calado, N. Daugbjerg & Ø. Moestrup. 2009. Ultrastructure and LSU rDNA-based revision of Peridinium group Palatinum (Dinophyceae) with the description of Palatinus gen. nov. Journal of Phycology 45: 1175-1194.

Hickel, B., & U. Pollingher. 1988 Identification of the bloom-forming Peridinium from Lake Kinneret (Israel) as P. gatunense (Dinophyceae). British Phycological Journal 23 (2): 115-119.

Horiguchi, T., & Y. Takano. 2006. Serial replacement of a diatom endosymbiont in the marine dinoflagellate Peridinium quinquecorne (Peridiniales, Dinophyceae). Phycological Research 54: 193-200.

Logares, R., K. Shalchian-Tabrizi, A. Boltovskoy & K. Rengefors. 2007. Extensive dinoflagellate phylogenies indicate infrequent marine–freshwater transitions. Molecular Phylogenetics and Evolution 45 (3): 887-903.

Mosses Have a Place for Reproduction

noreply@blogger.com (Christopher Taylor) — Mon, 05 Dec 2011 08:12:00 +0000

A Rhizogonium photographed in the Philippines by Leonardo L. Co.

The Rhizogoniaceae are a family of mosses found in tropical and subtropical parts of the world, with a concentration of diversity in the Southern Hemisphere. Many species in the family are epiphytic; in particular, many show a preference for growing on the trunks of tree ferns (O'Brien 2007). The family has been defined by features such as sharply toothed, usually bistratose (i.e. with two cell layers) leaves and sporophytes located in the basal half of the erect stems, but molecular studies have indicated that the Rhizogoniaceae in the broad sense are para- or polyphyletic, and for this post I'll be using Rhizogoniaceae in a more restricted sense, corresponding to the 'clade C' of O'Brien (2007), including genera such as Rhizogonium, Cryptopodium, Calomnium, Goniobryum and Pyrrhobryum. One member of the Rhizogoniaceae, Pyrrhobryum dozyanum, is often used in moss gardens (it appears that there may also be a moss doing the rounds under this name in the European aquarium trade, though I haven't found anything to confirm whether this species, also being referred to as "Mayaca fern" or "Indonesiae bogoriensis", is actually P. dozyanum. Many bryophytes and other such plants in the aquarium trade have been misidentified, sometimes dramatically so).

View under microscope of leaf of Pyrrhobryum dozyanum, showing the toothed margins characteristic of Rhizogoniaceae. Image from here.

Most attention on Rhizogoniaceae from an evolutionary point of view has focused on what they might say about the relationship between acrocarpy and pleurocarpy. To explain what these terms mean, we'll start with the following diagram (from here):

Like other plants, mosses go through an alternation of generations, with both haploid and diploid multicellular stages. The haploid stage of the life cycle, the gametophyte, is the leafy green part of the moss. The gametophyte produces perichaetia, whorls of modified leaves within which the gamete-producing organs are contained. When a female gamete is fertilised, the resulting diploid zygote grows into the sporophyte, the brown thread-like structure you will often see growing out of a moss. The sporophyte produces haploid spores that will be dispersed to grow into new leafy gametophytes.

The diagram above shows an acrocarpous moss, in which the perichaetium is produced at the end of a growing branch of the gametophyte. Other mosses, however, are pleurocarpous, with perichaetia produced on the side of a branch. Whether a moss is acrocarpous or pleurocarpous is one of the first things a botanist will look at when attempting to identify it. However, many Rhizogoniaceae do not easily fall on either side of the acrocarpous/pleurocarpous distinction. They are what is called cladocarpous: the perichaetia are produced at the ends of small side-branches. However, lest any moss enthusiasts accuse me of overly simplifying things, I must point out that a great deal has been written on the exact distinctions between acrocarpous vs cladocarpous vs pleurocarpous. Like so many distinctions in nature, there are examples that blur the distinction between these states. As the perichaetia-bearing side-branches in a cladocarpous moss get progressively shorter, they become less and less distinguishable from pleurocarpy. In light of this, recent authors have suggested that the distinction between cladocarpy vs pleurocarpy should be defined by whether or not the side-branch bearing a perichaetium also bears normal vegetative leaves. If it only bears perichaetial leaves, then it is pleurocarpous: by this definition, some Rhizogoniaceae (including the genus Rhizogonium) are truly pleurocarpous (Bell & Newton 2007).

Goniobryum subbasilare, photographed by David Tng.

The vast majority of pleurocarpous mosses belong to a clade called the Hypnanae, which is massively speciose (probably about half of living mosses are hypnanaens). Because the hypnanaen mosses are so successful, there is a lot of interest in their relationships with other mosses. And as it turns out, the Rhizogoniaceae (with their combination of cladocarpous and pleurocarpous members) are closely related to the Hypnanae. Indeed, the Hypnanae are nested within the older, paraphyletic grade referred to the Rhizogoniaceae (O'Brien 2007). The acrocarpous state is the plesiomorphic one for mosses, with cladocarpy evolving in numerous lineages. Pleurocarpous mosses, it seems likely, have then evolved from cladocarpous ancestors, though either a number of times or with a number of reversals.

REFERENCES

Bell, N. E., & A. E. Newton. 2007. Pleurocarpy in the rhizogoniaceous grade. In: Newton, A. E., & R. S. Tangney (eds) Pleurocarpous Mosses: systematics and evolution pp. 41-64. CRC Press.

O'Brien, T. J. 2007. The phylogenetic distribution of pleurocarpous mosses: evidence from cpDNA sequences. In: Newton, A. E., & R. S. Tangney (eds) Pleurocarpous Mosses: systematics and evolution pp. 19-40. CRC Press.

The Tuna-Lizards

noreply@blogger.com (Christopher Taylor) — Mon, 28 Nov 2011 09:07:00 +0000

The classic ichthyosaur Ichthyosaurus communis, from here.

Ichthyosaurs have long been one of the most famous examples of convergent evolution. These Mesozoic marine reptiles, as any textbook will tell you, evolved a body form similar to that of modern dolphins and sharks, and presumably held a similar niche as fast-swimming apex predators. But interesting as that might be, it's certainly not all there is to be said about ichthyosaurs.

The classic ichthyosaurs that said textbooks will usually depict are members of the clade Thunnosauria that first appeared in the upper Triassic (Thorne et al. 2011). Thunnosaurs differ from other ichthyosaurs in having a relatively short tail, shorter than the trunk, and hindfins that are much shorter than (usually less than half as long as) the forefins (Maisch & Matzke 2000). The name 'Thunnosauria' appropriately means 'tuna-lizards': as with modern tunas, the compact body of the thunnosaurs indicates greater specialisation for more powerful, tail-driven swimming.

Cast of the short-beaked Ichthyosaurus breviceps, from Charmouth Heritage Coast Centre.

In the Lower Jurassic, thunnosaurs are represented by the genera Ichthyosaurus and Stenopterygius, though the known fossil record for the former is earlier than that of the latter. Both genera are represented by hundreds (if not thousands in the case of Stenopterygius) of known specimens from Europe (Motani 2005): primarily England for Ichthyosaurus, Germany for Stenopterygius. Stenopterygius grew up to 4 m in length; Ichthyosaurus would have been somewhat smaller (Maisch & Matzke 2000). One species of Ichthyosaurus, I. breviceps, stands out for its particularly short and robust rostrum in comparison to other species. Another potential Lower Jurassic thunnosaur is Hauffiopteryx typicus, which also has a distinctively small rostrum, but in this case a particularly fine and slender one (Maisch 2008).

Mounted skeleton of Ophthalmosaurus icenicus, from the British Natural History Museum.

During the Lower Jurassic, the thunnosaurs were among a number of ichthyosaur lineages present. By the time of the Upper Jurassic, all surviving ichthyosaurs (with one possible exception*) belonged to a single thunnosaur lineage, the Ophthalmosauridae. Unfortunately, for most of the Middle Jurassic the ichthyosaur fossil record is missing, and a gap of more than ten million years separates Stenopterygius from Ophthalmosaurus. The only break in this gap is the Argentinan Chacaicosaurus cayi, which sits a few million years later than Stenopterygius. Intriguingly, Chacaicosaurus is not only intermediate in age, it is intermediate in morphology: while its skull is similar to that of Ophthalmosaurus, its forefin is more similar to that of Stenopterygius. As noted by Maisch & Matzke (2000), "It appears as if Chacaicosaurus cayi is one of the rare forms that are true structural intermediates".

*The possible exception is the Upper Jurassic Nannopterygius enthekiodon, some features of which suggest that it occupies a more basal Stenopterygius-grade position (Maisch & Matzke 2000). Unfortunately, it has not yet been adequately described and included in a formal phylogenetic analysis. This is rather frustrating: Nannopterygius promises to be a quite distinctive animal, with greatly reduced fins and long spinal processes on the anterior tail vertebrate.

Reconstruction of Platypterygius bannovkensis, by Olorotitan. Platypterygius was the latest surviving ichthyosaur genus.

The ophthalmosaurids survived from the late Middle Jurassic to the early Upper Cretaceous. Ophthalmosaurus had a slender rostrum with reduced dentition, while other genera such as Brachypterygius and Platypterygius had higher, more robust rostra with their full complement of teeth. Some ophthalmosaurids grew very large: Platypterygius reached up to 9 m. The name Ophthalmosaurus means 'eye lizard', and reference to the large eyes of this ichthyosaur seems to be de rigeur for any popular book in which it features, together with some speculation that it may have been a nocturnal hunter. However, a quick scan through the various ichthyosaur skulls illustrated by Maisch and Matzke (2000) indicates that ichthyosaur eyes were generally large. Those of Ophthalmosaurus were not the largest; the eyes of Eurhinosaurus longirostris are particularly ridiculous, with orbits filling almost the entire side of the cranium! So perhaps the question should not be why Ophthalmosaurus had large eyes, but why those ichthyosaurs without large eyes had reduced them.

REFERENCES

Maisch, M. W. 2008. Revision der Gattung Stenopterygius Jaekel, 1904 emend. von Huene, 1922 (Reptilia: Ichthyosauria) aus dem unteren Jura Westeuropas. Palaeodiversity 1: 227-271.

Maisch, M. W., & A. T. Matzke. 2000. The Ichthyosauria. Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 298: 1-159.

Motani, R. 2005. True skull roof configuration of Ichthyosaurus and Stenopterygius and its implications. Journal of Vertebrate Paleontology 25 (2): 338-342.

Thorne, P. M., M. Ruta & M. J. Benton. 2011. Resetting the evolution of marine reptiles at the Triassic-Jurassic boundary. Proceedings of the National Academy of Sciences of the USA 108 (20): 8339-8344.

The Source

noreply@blogger.com (Christopher Taylor) — Sun, 27 Nov 2011 07:10:00 +0000

I was taking some photos today of the new house to send to my parents in New Zealand, when I thought I might take some extras to put up here and demonstrate the current state of my office. You never know, someone might be interested. I'm somewhat anachronistic in that I do still largely work from printed material rather than pdfs, and the ghosts of a thousand trees probably haunt my workspace.

The person who is able to identify the most of the books visible in these photos wins the grand prize of having identified the most books in these photos. Of course, most of my reference collection is not quite so photogenic:

Most of my papers lurk in large filing cabinets, while the boxes contain copies of particularly lengthy papers and out-of-print or otherwise unobtainable books that I haven't yet gotten ring-bound like the ones on the shelves.

Hat-tip to Darren Naish, of whom this post is something of a blatant rip-off.

Tetragraptines

noreply@blogger.com (Christopher Taylor) — Tue, 22 Nov 2011 06:47:00 +0000

Colonies of Tetragraptus quadribrachiatus, from the University of Oslo.

In preparation for this post, I have been attempting to develop an understanding of graptolite branching patterns. This is not something that should be attempted lightly, if at all. If anything in this post seems confused, it's because it is.

The Tetragraptinae were a group of graptolites that lived during the Lower Ordovician, and formed part of the early radiation of planktonic graptoloids. In one of the earlier phylogenetic (or at least quasi-phylogenetic) classifications of graptolites, that of Fortey & Cooper (1986), the tetragraptines (including the genera Tetragraptus and Pseudophyllograptus) were recognised on the basis of what was called the 'Tetragraptus serra proximal type'. In an earlier post, I explained how graptolite colonies grew as a series of branching zooids (individuals). The colony section for each individual zooid is called the theca, and graptolite workers usually refer to the thecae in discussions rather than the zooids (as the zooids are generally not preserved in fossils). A developing colony starts with the initial larval zooid, called the sicula. Out of the side of the sicula grows the first mature theca, which is referred to as th1¹ (the sicula is not included in the thecal count because it has a different growth pattern from the sequential thecae). The second theca, th1², then buds off from th1¹. The third theca to arise is th2¹, then th2², then th3¹, and so on and so forth. If all these bud in a simple sequence, the colony is not branching. However, if one or more of these basal thecae is what is known as a dicalycal theca (it produces two daughter thecae instead of just one), the colony branches. In most tetragraptines, th1² is a dicalycal theca, as are its two daughter thecae, so the mature colony has four branches. The basal canals of th1² and th2¹ crossing over the sicula, plus the proximal part of th2², make the lower part of the proximal region very robust: this massiveness is what characterises the Tetragraptus serra proximal type. Other characters listed by Fortey & Cooper (1986) as synapomorphies for the Tetragraptinae, reclined colony branches and a reduction in the number of branches, were also found in other lineages.

Proximal region of Tetragraptus bigsbyi, showing robust morphology, together with diagrammatic representation of thecal connections in early colony. From Bulman (1970).

The Tetragraptinae were one of a number of groups of Ordovician graptolites with four-branched colonies, though other taxa lacked the T. serra proximal region. In a phylogenetic analysis of graptoloids, Maletz et al. (2005) identified four-branched graptoloids as a single clade that they called the Tetragrapta. This is in contrast to Fortey & Cooper (1986), who placed these taxa at a number of places in the graptoloid tree. The analysis of Maletz et al. (2005) differed from that of Fortey & Cooper (1986) in being a computational analysis rather than being constructed 'by hand'. Some characters given high weight by Fortey & Cooper (1986), such as the presence of a structure called a virgella, were found to be less significant by Maletz et al. (2005). However, in some regards the coverage of the latter study was less complete than the earlier. Most notable for the present post is that Fortey & Cooper (1986) had also included 'Dichograptus' solidus in the Tetragraptinae. This species apparently also has the T. serra proximal region, but also has more than four branches in the colony. It is possible that its inclusion in a computational analysis would weaken the association of four-branched graptoloids as a clade.

By the end of the Ordovician, the graptoloid lineages with multi-branched colonies were extinct. There have been numerous suggestions for why this may have happened—buoyancy issues or competition between zooids are among the front runners—but for the rest of graptoloid history, simplicity would become the watchword.

REFERENCES

Bulman, O. M. B. 1970. Graptolithina with sections of Enteropneusta and Pterobranchia. In Treatise on Invertebrate Paleontology Part V 2nd ed. (C. Teichert, ed.) pp. V1-V149. The Geological Society of America, Inc.: Boulder (Colorado), and the University of Kansas: Lawrence (Kansas).

Fortey, R. A., & R. A. Cooper. 1986. A phylogenetic classification of the graptoloids. Palaeontology 29: 631-654.

Maletz, J., J. Carlucci & C. E. Mitchell. 2009. Graptoloid cladistics, taxonomy and phylogeny. Bulletin of Geosciences 84 (1): 7-19.

Life on Mars: the Cambrian terrestrial environment

noreply@blogger.com (Christopher Taylor) — Wed, 16 Nov 2011 06:45:00 +0000

The question of when life first moved onto the land has been the subject of speculation for as long as anyone has realised that there was a 'first' to speculate about. Established terrestrial communities were clearly present by the latter part of the Silurian, but was there anything earlier? The reasonable expectation is that there was, at least on some level. Pretty much as soon as there was life inhabiting the oceans in prokaryote form, weather cycles would have been carrying bacteria and their spores onto their land. It is not unreasonable to assume that some of them may have been able to acquire a toehold in some attainable niche, and from there diversify to the surrounding environment. Later, other microbial and simple organisms may have joined them. But such organisms leave little trace in the fossil record. What were they like, how did they live? A paper that has just been published in Palaeontology (Retallack 2011) has described simple terrestrial fossils preserved from the Middle Cambrian, and may provide a rare glimpse of the early Earth.

Reconstruction of Cambrian terrestrial biota from Retallack (2011).

The remains described by Retallack (2011) are extremely simple: flat, thallose impressions called Farghera, subterranean threads known as Prasinema and buried ovoid structures called Erytholus. All of these are described as form taxa: that is, they represent a particular recognisable fossil structure whose relationship to other such fossils is unknown. Different form taxa may even represent different parts of a single organism.

The linear, branching Farghera thalli were an average of just under 2 mm wide, though they could get much wider, and preserved thalli are often several centimetres in length. The living thalli would have been similar to an alga or lichen, either of which they could have been. The thread-like Prasinema are preserved as a central filament less than 1 mm in diameter, surrounded by a dark halo up to about 2.5 mm across. It seems likely that only the central filament represents the original central organism; the halo would have formed by microbes growing around the filaments as they decayed. Prasinema filaments could apparently grow to 30 cm beneath the original soil surface, and probably represent structures similar to fungal hyphae.

Most unusual are the Erytholus, globose structures up to 2 cm in diameter, divided into internal layers with a broad central column. Retallack (2011) suggests a number of possible interpretations for Erytholus: vendobiont or xenophyophore (unlikely because of the terrestrial location), alga (again unlikely, because it is both terrestrial and buried beneath the surface), or fungal or slime mold reproductive structures, comparable to truffles. However, the truffle interpretation is problematic because truffles are produced to disperse spores through being eaten by animals. Obviously, this could not have been the case in the terrestrial Cambrian! A further possibility that I can think of is that Erytholus may have been some sort of resting structure, analogous to a plant bulb or tuber (though note that this interpretation would not necessarily exclude a reproductive function).

As with the Silurian, I think it is important to remember that the environment would have been very different in those days in more ways than one might immediately think. There are parts of the world today where lichens and algae remain the primary ground cover, but we should be careful in assuming that such spots are close analogues of the Cambrian terrestrial environment. Such areas are today arid and/or highly eroded, but in the Cambrian lichens and algae would have also been able to dominate areas in which vascular plants would overshadow them today. I also find myself again wondering what effect the absence of a complex vegetation profile might have had on weather patterns at the time. Would winds have been stronger if there were less low-level wind breaks? Would the effects of rain events have been more catastrophic if water flow was less impeded by ground-cover (if Erytholus was indeed a sort-of-tuber, perhaps it functioned as a source of regrowth if the above-ground component of the organism was destroyed by weather?) If we could see the Cambrian environment for ourselves, there could be no doubt that we would find it utterly alien.

REFERENCE

Retallack, G. J. 2011. Problematic megafossils in Cambrian palaeosols of South Australia. Palaeontology 54 (6): 1223-1242.

Nerites Old and New

noreply@blogger.com (Christopher Taylor) — Mon, 14 Nov 2011 06:53:00 +0000

Four-toothed nerites Nerita versicolor, from here. Some tropical nerite species can be vary variable in their patterning.

Like many New Zealand kids, I spent a large number of my early days at the beach (my great-grandparents and great-uncle lived beside a bay near Pataua north of Whangarei, and we used to camp there most summers). Most of my time at the beach tended to be occupied with the search for animals under rocks: mud crabs, snapping shrimp, whelks, even the occasional worm. The tops of the rocks would be home to oysters and nerites, and if you pulled a nerite off the rock you could see it close itself up, hiding behind its green and white operculum.

At the time, I wasn't aware of much difference between the nerites and any other marine snail, but there is one. Nerites and their allies, the Neritimorpha (sometimes called Neritopsina) are one of the major basal lineages among gastropods. They have a distinctive protoconch (larval shell), with closely convolute whorls (Frýda & Heidelberger 2003). Most living neritimorphs also dissolve out the columella, the central whorl of the shell, as they grow, so the interior of the shell is a single open cavity. Their shells lack nacre, and are closed with an operculum.

The fossil record of neritimorphs stretches back to the Palaeozoic, though the crown group probably originated close to the Permian-Triassic boundary (Nützel et al. 2007). Among taxa identified as stem neritimorphs in the Palaeozoic are the Naticopsidae (named for their superficial resemblance to the living moon snails, Naticidae) and the Platyceratidae, open-whorled forms that include species found in apparent symbiotic associations with other invertebrates such as crinoids. However, the discovery of preserved protoconches in some 'platyceratids' have demonstrated that, while some species had protoconches comparable to those of modern neritimorphs, others had distinctive open hook-like protoconches unlike those of any other gastropod (Frýda et al. 2009). Those species with the hook-shaped protoconches have been separated out as the Cyrtoneritimorpha, while the modern neritimorphs and those with comparable protoconches are called the Cycloneritimorpha. Despite the similarities in adult shell form between cyrtoneritimorphs and cycloneritimorphs, the distinct protoconch form suggests that the two lineages may not be closely related. However, no features have been identified as yet aligning cyrtoneritimorphs with any other gastropod group, and their true affinities are a mystery.

Neritopsis radula, from here.

Among the crown group neritimorphs, the two living species of the genus Neritopsis are distinctive in being the only species to retain the columella, and molecular analysis corroborates this morphological distinction in identifying Neritopsis as basally divided from most other neritimorphs (Kano et al. 2002). Neritopsis does form a clade with the genus Titiscania, but questions of columella retention are irrelevant for that genus, as its two species lack a shell entirely (instead, they protect themselves from predators by discharging white threads from glands on their back). Neritopsids were abundant during the Mesozoic, but became progressively rarer from about the mid-Cenozoic. The living species of Neritopsis and Titiscania are found in secluded habitats such as submarine caves and crevices under rocks.

The terrestrial neritimorph Helicina clappi, photographed by Robert Pilla.

The clade formed by the remaining neritimorphs was more successful, containing about 450 living species. As well as marine species, they include a number of brackish- or fresh-water taxa, and two families (the Hydrocenidae and Helicinidae) of terrestrial snails. Members of the family Phenacolepadidae are mostly limpet-shaped inhabitants of low-oxygen, sulphide-rich environments underneath rocks or sunken logs. Other families such as the Neritidae have remained mostly more conservative (though the Neritidae also include a limpet-like genus, Septaria), but are widespread throughout the world. The species I encountered as a child, offhand, was Nerita melanotragus—and if anyone out there can tell me why a small snail should have been given a name that appears to mean 'black goat', I'd be interested to know.

REFERENCES

Frýda, J., & D. Heidelberger. 2003. Systematic position of Cyrtoneritimorpha within the class Gastropoda with description of two new genera from Siluro-Devonian strata of Central Europe. Bulletin of the Czech Geological Survey 78 (1): 35-39.

Frýda, J., P. R. Racheboeuf, B. Frýdová, L. Ferrová, M. Mergl & S. Berkyová. 2009. Platyceratid gastropods—stem group of patellogastropods, neritimorphs or something else? Bulletin of Geosciences 84 (1): 107-120.

Kano, Y., S. Chiba & T. Kase. 2002. Major adaptive radiation in neritopsine gastropods estimated from 28S rRNA sequences and fossil records. Proc. R. Soc. Lond. B 269: 2457-2465.

Nützel, A., J. Fŕyda, T. E. Yancey & J. R. Anderson. 2007. Larval shells of Late Palaeozoic naticopsid gastropods (Neritopsoidea: Neritimorpha) with a discussion of the early neritimorph evolution. Paläontologische Zeitschrift 81 (3): 213-228.

What to do with a Dead Hummingbird

noreply@blogger.com (Christopher Taylor) — Fri, 11 Nov 2011 04:36:00 +0000

We've all been there: that dead hummingbird is just cluttering things up, you don't really know what to do with it, but you don't really want to throw it out because, hey, you never know when that sort of thing might come in handy. Well, fear not! A dead hummingbird can be a very practical thing:

You need never be without a scale bar again!

The above figure, from Archibald et al. (2011), shows a rufous hummingbird Selasphorus rufus alongside the newly described early Eocene giant ant Titanomyrma lubei. This fossil comes from the American Green River Formation, in present-day Wyoming. At 51 mm in length, this is one of the largest known ants, rivalled in the modern fauna only by the marginally longer but possibly less robust driver ant Dorylus wilverthi (I wrote about driver ants in an earlier post). The title of largest ant ever goes, so far as we know, to Titanomyrma giganteum (or Formicium giganteum*) from the Messel Formation of Germany.

*There's a bit of skullduggery in Archibald et al.'s paper viz. the relative status of the pre-existing genus Formicium and their new genus Titanomyrma, whereby Titanomyrma is not diagnostically different from Formicium, but Formicium is relegated to the status of a form taxon for wing fossils only. This is all above board, ICZN-wise, but I'm not sure I'd condone it.

Living giant ants (which, except for Dorylus, are all under 35 mm) are mostly tropical in distribution, but the locality from which Titanomyrma lubei hails would have been within the Arctic Circle when it was alive (Update: Neil has corrected me: the Green River Formation was not Arctic, but northern temperate). The Eocene was a much seamier time than today and, though not tropical, the Arctic would have been far from a frozen wasteland.

REFERENCE

Archibald, S. B., K. R. Johnson, K. W. Mathewes & D. R. Greenwood. 2011. Intercontinental dispersal of giant thermophilic ants across the Arctic during early Eocene hyperthermals. Proceedings of the Royal Society of London Series B—Biological Sciences 278 (1725): 3679-3686.

Ants Go Out in the Noonday Sun

noreply@blogger.com (Christopher Taylor) — Tue, 08 Nov 2011 05:49:00 +0000

Furnace ants Melophorus carrying a dead earwig back to the colony. Despite the size range visible in the photo, all represent a single species. Photographed by Alex Wild.

If there is one group of organisms that you are guaranteed to see anywhere you go in Australia, it is ants. Especially in the inland arid parts of the country, ants are generally the most prominent insects to remain active and visible during the daylight hours, and they are perhaps the best-studied group of Australian insects (mind you, I work in a lab inhabited primarily by ant specialists, so my impression may be biased).

Melophorus, the subject of today's post, is a genus of ants unique to Australia. It is a member of the Formicinae, the clade of ants distinguished by the production of formic acid through an acidopore at the end of the abdomen, and its species are distinguished from related genera by their slit-shaped propodeal spiracle, metapleural gland and antennae inserted close to the posterior margin of the clypeus. About thirty species have been described to date, but this number is undoubtedly low: for instance, of the 30+ morphospecies identified from the south-west corner of Western Australia, only about a quarter represent named species (Heterick 2009). Estimates of species numbers are complicated by the fact that most, if not all, Melophorus species are polymorphic, though variation is continuous rather than into discrete castes.

Emerging young queen (the large red winged individual) and males (smaller, black) of Melophorus bagoti, from Ken Cheng.

The highest diversity of Melophorus species is found in arid environments, where they forage during the daytime. The best-studied species, the Australian honeypot ant Melophorus bagoti, has the highest recorded heat tolerance of any ant, and forages in air temperatures above 50°C, with ground temperatures in excess of 70°C (Christian & Morton 1992). Foragers of M. bagoti mostly collect the carcasses of dead insects that have expired in the heat, though they will also collect plant material such as seeds and liquid foods such as nectar (other Melophorus species may focus on the latter food supplies). Despite their high heat tolerance, the M. bagoti workers are working on the knife-edge: about one-fifth of a colony's foragers will die each day in these punishing conditions, and the average life expectancy for a forager is only about five days (Muser et al. 2005). Indeed, Muser et al. (2005) estimated that the average forager only makes one successful food collection during its working life, and suggested that the bulk of a colony's food supply was derived from a relatively small core of foragers that managed to beat the odds (the longest forager career they recorded was at least 27 days).

Repletes of Melophorus hanging from a colony ceiling, photographed by Sarah Tahourdin.

Melophorus bagoti is known as the honeypot ant* because, in addition to the normal workers, the colony is home to specialised workers called repletes. The repletes do not leave the colony to forage; in fact, they probably barely move at all. Foragers collecting liquid food will, upon returning to the colony, pass their collections on to a replete. The replete's abdomen swells enormously as it fills with food, transforming the replete into a living food store, ready to pass its cache back to hungry workers that approach it for feeding. Needless to say, honeypot repletes are also of interest to predators, including humans, who are quite happy to take advantage of these sweet pre-packaged morsels when they find them.

*Melophorus species as a whole have been called 'furnace ants' due to their high heat tolerance.

Repletes, frozen and used to add flair to desserts. Photograph by Peter Menzel.

It has been suggested that Melophorus species became specialists in high temperatures as this avoided competition with the Iridomyrmex meat ants that dominate the Australian daytime ant fauna. Iridomyrmex species are large and aggressive, and effectively exclude most other species from competing with them. However, a small number of Melophorus species not only do not seem to avoid Iridomyrmex, but actually seek out their company. Melophorus anderseni mingles with workers of Iridomyrmex sanguineus entering and exiting their nest, from which it steals larvae and carries them back to its own nest, located alongside the Iridomyrmex nest but having smaller entrances that the large Iridomyrmex cannot enter. Melophorus anderseni workers are apparently able to avoid detection by the Iridomyrmex as they rub against them to pick up the meat ant's scent. Though the Iridomyrmex have not been observed taking action agains the Melophorus themselves, they have been observed using pebbles to block off the entrances to the Melophorus nest (Agosti 1997).

REFERENCES

Agosti, D. 1997. Two new enigmatic Melophorus species (Hymenoptera: Formicidae) from Australia. Journal of the New York Entomological Society 105 (3-4): 161-169.

Christian, K. A., & S. R. Morton. 1992. Extreme thermophilia in a central Australian ant, Melophorus bagoti. Physiological Zoology 65 (5): 885-905.

Heterick, B. E. 2009. A guide to the ants of south-western Australia. Records of the Western Australian Museum Supplement 76: 1-206.

Muser, B., S. Sommer, H. Wolf & R. Wehner. 2005. Foraging ecology of the thermophilic Australian desert ant, Melophorus bagoti. Australian Journal of Zoology 53: 301-311.

Disco Opilioni

noreply@blogger.com (Christopher Taylor) — Mon, 31 Oct 2011 12:30:00 +0000

As I do every week, I spun the wheel yesterday to find out what the topic for this week's post would be. It told me to write about Cristina. Interesting, I thought, this site doesn't usually focus on early 1980s No Wave performers:

But then, of course, I realised that I'd driven that cheap gag about as far as I could (not very far, as it turned out). The actual topic of today's post is the African harvestman genus Cristina.

Male Cristina armata, from Roewer (1911).

As is not unusual, the harvestman fauna of Africa has been far less extensively studied than that of other continents. Among the long-legged harvestmen, to which Cristina belongs, most known African species belong to the family Phalangiidae, again including Cristina. Two species of Neopilionidae (Neopilio australis and Vibone vetusta) are known from the very south of the continent, and various species of Sclerosomatidae are known from the very north (which, biogeographically speaking, is more part of Europe than Africa, at least as far as harvestmen are concerned). Otherwise, the continent is the preserve of the phalangiids, and Africa is home to the world's only tropical Phalangiidae. What is known of the African phalangiid fauna was mostly reviewed by Staręga (1984).

Cristina is found in eastern African from the Horn south to Mozambique, with an outlying species across the Gulf of Aden in Yemen. Cristina species are also known from central Africa, Ghana and Togo, and it is likely found in a broad band across the entirety of central Africa. Like many other genera of phalangiids, Cristina has transverse rows of spines across the body, but it is distinguished from most confamilials by the presence of four (sometimes two) pairs of denticles or large spines on the eye mound (Cristina crassipes from Togo has the last pair of spines directed backwards and almost looking like a pair of horns). The males have the first pair of legs distinctly swollen in comparison to the remaining legs, but do not have particularly modified chelicerae.

We don't as yet know how the African phalangiids are related to those elsewhere. The Phalangiidae tend, underneath their superficial spines, to be a fairly conservative bunch, and will not reveal themselves easily.

REFERENCES

Roewer, C.-F. 1911. Übersicht der Genera der Subfamilie der Phalangiini der Opiliones Palpatores nebst Beschreibung einiger neuer Gattungen und Arten. Archiv für Naturgesichte 77 (Suppl. 2): 1-106.

Staręga, W. 1984. Revision der Phalangiidae (Opiliones), III. Die afrikanischen Gattungen der Phalangiinae, nebst Katalog aller afrikanischen Arten der Familie. Annales Zoologici 38 (1): 1-79.

Ginseng and Ivy

noreply@blogger.com (Christopher Taylor) — Mon, 24 Oct 2011 06:10:00 +0000

Pate Schefflera digitata, photographed by Kahuroa.

The Araliaceae are a family of nearly 1500 species of flowering plants found around the world, but primarily in the Old World tropics. Most of its members are trees or shrubs, but there are also some herbaceous or climbing species. Many Araliaceae have palmate leaves, and they often produce inflorescences in umbels. Not that many Araliaceae hold much economic prominence: Tetrapanax papyriferus is used to make rice paper, while the genus Panax includes the ginsengs that are widely regarded as something of a wonder-drug for no apparent good reason. Some other species are well known as garden plants, such as ivy Hedera helix. Back in my home country of New Zealand, Araliaceae include some of the most familiar small native trees such as pate Schefflera digitata and the five-fingers and lancewoods of the genus Pseudopanax.

A young lancewood Pseudopanax crassifolius, photographed by Mike Hudson. Lancewood is notable for its differing growth habits over its lifespan: this individual is just beginning to change from its juvenile to its mature foliage. When the plant is young, the long, narrow, tooth-edged leaves hang down around the trunk. As the tree matures, it produces leaves that are shorter, broader and with less strong teeth, and that are held upwards and outwards. The juvenile and mature trees are so different in appearance that they were initially described as different species.

The Araliaceae have long been recognised as close relatives of the Apiaceae, the family including carrots and celery, to the extent that some authors have combined the two in a single family. Most recent researchers have maintained the distinction, but phylogenetic studies have indicated that some genera previously treated within the Apiaceae, notably the water and marsh pennyworts of the genus Hydrocotyle, are better treated as basal Araliaceae (Plunkett et al. 1997). Relationships within the Araliaceae are somewhat less straightforward, as molecular phylogenetic studies have indicated that there has been a great deal of homoplasy in morphological characters (Plunkett et al. 2004). Some of the larger genera in the family (notably the genus Schefflera, to which nearly half the species of Araliaceae have been assigned) appear to be significantly polyphyletic, some of them not even resolving in particularly proximate clades. The difficult nature of many araliaceous genera has long been realised: in 1868, the botanist Berthold Seemann referred to the then-poorly defined Panax as "one of the great lumber rooms of our science" (Wen et al. 2001).

American ginseng Panax quinquefolius, from here. Red ginseng is derived from the root of this species and the Asian P. ginseng; however, over-harvesting has lead to the endangerment of wild populations of the latter.

REFERENCES

Plunkett, G. M., D. E. Soltis & P. S. Soltis. 1997. Clarification of the relationship between Apiaceae and Araliaceae based on matK and rbcL sequence data. American Journal of Botany 84 (4): 565-580.

Plunkett, G. M., J. Wen & P. P. Lowry II. 2004. Infrafamilial classifications and characters in Araliaceae: Insights from the phylogenetic analysis of nuclear (ITS) and plastid (trnL-trnF) sequence data. Plant Systematics and Evolution 245 (1-2): 1-39.

Wen, J., G. M. Plunkett, A. D. Mitchell & S. J. Wagstaff. 2001. The evolution of Araliaceae: a phylogenetic analysis based on ITS sequences of nuclear ribosomal DNA. Systematic Botany 26 (1): 144-167.

The Alga of Uncertainty

noreply@blogger.com (Christopher Taylor) — Wed, 19 Oct 2011 05:18:00 +0000

The red alga Rhodomela confervoides, from Coastal Imageworks.

The tradition in taxonomy that nothing is ever really forgotten (for which there are very good reasons) means that, over the years, we have accumulated a certain amount of excess detritus. Whether referred to as nomina dubia, species inquirendae or just plain unidentifiable, there are a number of names for which the original description or material is not adequate to determine their identity with certainty. Most nomina dubia simply slumber undisturbed, not interfering with standard taxonomic practice; they simply serve to irritate those whose role it is to assemble comprehensive listings.

The red alga Rhodomela preissii was named by Sonder in 1848 for a specimen collected in Western Australia. He diagnosed it as "fronde tereti filiformi siccitate subplicata a basi dichotome ramosa, ramis inferioribus patentibus superioribus brevioribus erectiusculis, ramulis sparsis setaceis simplicibus furcatisve, capsulis subpedicellatis solitariis ramis superioribus adnatis", Latin descriptions being the fashion at the time*. The specimen appears to have never been figured.

*Some of you may be aware that the Botanical Congress recently voted to remove the requirement for Latin diagnoses or descriptions from the Botanical Code of Nomenclature**. Authors are still required to give a diagnosis for new taxa in either Latin or English, so Chinese still doesn't get a look-in.

**Though it was also decided that it would no longer be called the Botanical Code. It's now the "International Code of Nomenclature for Algae, Fungi and Plants". I suppose that we should be just grateful they didn't go with the even more explicit "International Code of Nomenclature for Plants, Fungi, Algae, Oomycetes, Labyrinthuleans, Plasmodiophoromycetes, Mycetozoans, Dinoflagellates, Euglenaceae and Cyanobacteria (and maybe Fossil Bacteria, on alternate Tuesdays)".

Hypnea rosea, photographed by Olivier De Clerck.

Womersley (2003) noted that the type specimen of Rhodomela preissii, held at the Melbourne herbarium, is small and inadequate for the species' identification. True Rhodomela is unknown from Australia, though other members of the Rhodomelaceae occur there. Womersley, however, suggested that R. preissii might be a specimen of Hypnea. If true, this would place 'R.' preissii some distance phylogenetically from Rhodomela, the latter belonging to the order Ceramiales while Hypnea is a member of the Gigartinales. As things stand, though, no-one seems to be faced with a great need to resolve the question.

REFERENCES

Sonder, O. G. 1846-1848. Algae L. Agardh. In: Lehmann, C. Plantae Preissianae sive Enumeratio Plantarum quas in Australasia occidentali et meridionali-occidentali annis 1838-1841 collegit Ludovicus Preiss, Phil. Dr. Acad. Caesar. Leopold, Carol. Natur. Curios. et Reg. Societ. Bot. Ratisbonens, Sodalis, cet. vol. 2 pp. 148-160 (1846), 161-195 (1848). Meissner: Hamburg.

Womersley, H.B.S. 2003. The Marine Benthic Flora of Southern Australia.
Rhodophyta. Part IIID. Ceramiales – Delesseriaceae, Sarcomeniaceae, Rhodomelaceae. Australian Biological Resources Study, Canberra.

Groundhogs, Woodchucks and Other Big Squirrels

noreply@blogger.com (Christopher Taylor) — Tue, 11 Oct 2011 00:27:00 +0000

Thirteen-lined ground squirrel Ictidomys tridecemlineatus, photographed by Phil Myers.

The Holarctic ground squirrels of the Marmotini were the subject of one of my earliest posts at this site, before I really knew what I was doing*. So I'll have a go at improving it now.

*Not, of course, that I know what I'm doing now.

The Arctic ground squirrel Urocitellus parryii, photographed by Ianaré Sévi.

Marmotini is the clade of squirrels that includes ground squirrels (Spermophilus), antelope ground squirrels (Ammospermophilus), marmots (Marmota) and prairie dogs (Cynomys). Authors seem to differ on whether to also include the chipmunks (Tamias), but the question is somewhat semantic: agreement seems to be universal that the chipmunks represent the sister group to the remaining marmotins (Herron et al. 2004), so the only real question is how inclusive one wishes to make the term. The Chinese rock squirrels Sciurotamias may also belong to the Marmotini (Steppan et al. 2004). Except for the semi-arboreal chipmunks, marmotins are largely terrestrial in habits. They nest in underground burrows (including chipmunks), and some species form quite complex societies.

Père David's rock squirrel Sciurotamias davidianus, from here.

Ground squirrels previously assigned to the genus Spermophilus* have a wide range through Eurasia and North America. However, both morphological and molecular data indicate that Cynomys is derived from within 'Spermophilus', and molecular data indicate that Ammospermophilus and Marmota are as well (Herron et al. 2004). Helgen et al. (2009) divided the former Spermophilus between eight genera. Six of these genera are found in North America, one (Spermophilus proper) is found in Eurasia, and only one (Urocitellus) spans the divide between northeast Asia and North America. Whether the Marmotini as a whole are Eurasian or North American in origin is equivocal: of the three basalmost branches, Sciurotamias is definitely Eurasian, Tamias could be either (the Siberian chipmunk Tamias sibiricus is the sister to the remaining North American species) and the Spermophilus clade is probably North American in origin, with dispersals back to Eurasia in Marmota, Urocitellus and Spermophilus (Herron et al. 2004).

*Particularly in the European literature, it was not uncommon in the past to find the name Citellus being used in place of Spermophilus. Citellus Oken 1816 is indeed an older name than Spermophilus Cuvier 1825; however, the publication that the former derives from was not one that used the binomial system, and hence it has been declared invalid as a source of names (International Commission on Zoological Nomenclature 1956).

The woodchuck Marmota monax, from here.

Marmotins were the dominant squirrel group in North America during the Neogene; tree squirrels, though present, were exceedingly rare (Emry et al. 2005). The Pliocene Paenemarmota was the largest of all marmotins, reaching the size of a large beaver (Repenning 1962).

REFERENCES

Emry, R. J., W. W. Korth & M. A. Bell. 2005. A tree squirrel (Rodentia, Sciuridae, Sciurini) from the Late Miocene (Clarendonian) of Nevada. Journal of Vertebrate Paleontology 25 (1): 228-235.

Helgen, K. M., F. R. Cole, L. E. Helgen & D. E. Wilson. 2009. Generic revision in the Holarctic ground squirrel genus Spermophilus. Journal of Mammalogy 90 (2): 270-305.

Herron, M. D., T. A. Castoe & C. L. Parkinson. 2004. Sciurid phylogeny and the paraphyly of Holarctic ground squirrels (Spermophilus). Molecular Phylogenetics and Evolution 31: 1015-1030.

International Commission on Zoological Nomenclature. 1956. Opinion 417. Rejection for nomenclatorial purposes of volume 3 (Zoologie) of the work by Lorenz Oken entitled Okens Lehrbuch der Naturgeschichte published in 1815–1816. Opinions and Declarations Rendered by the International Commission on Zoological Nomenclature 14: 1–42.

Repenning, C. A. 1962. The giant ground squirrel Paenemarmota. Journal of Paleontology 36 (3): 540-556.

Steppan, S. J., B. L. Storz & R. S. Hoffmann. 2004. Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1. Molecular Phylogenetics and Evolution 30: 703-719.

The Long-Whipped Bryozoan

noreply@blogger.com (Christopher Taylor) — Tue, 04 Oct 2011 05:16:00 +0000

Zooids of Crepidacantha longiseta, from Tillbrook et al. (2001).

Coral is far from being the only organism involved in the construction of a coral reef. Other calcareous organisms such as coralline algae, foraminifera and molluscs may also be significant. And, of course, there are those delicate artistes known as bryozoans. Many bryozoans tend to be underestimated as reef components because, as well as being relatively small, they often prefer to settle in more cryptic habitats such as around and under coral gravel (Kobluk et al. 1988).

The organism in the SEM photo at the top of this post is one reef-inhabiting bryozoan, Crepidacantha longiseta. This species belongs to the ascophoran bryozoans, i.e. the zooid is protected dorsally by a calcified frontal wall, and each feeding zooid is associated with two long whip-like avicularia (the exact function of bryozoan avicularia is debated, but they are generally believed to be related to defense and/or cleaning the surface of the colony). In the top image, the feeding zooids are represented by the keyhole- or cartoon-fish-shaped openings, while the avicularia are positioned to either side of the main opening. Other Crepidacantha species may have the avicularia in different positions; they also differ in the length of the avicularia and the shape of the primary orifice (Tilbrook et al. 2001).

Crepidacantha longiseta is found in cryptic habitats around coral gravel in shallower waters, but may be found in more exposed positions as the water gets deeper, below about 25 m (Martindale 1992). It has been found in Vanuatu, Brazil, the Caribbean and Mauritius, and is presumably pantropical in its distribution (Tilbrook et al. 2001).

REFERENCES

Kobluk, D. R., R. J. Cuffey, S. S. Fonda & M. A. Lysenko. 1988. Cryptic Bryozoa, leeward fringing reef of Bonaire, Netherlands Antilles, and their paleoecological application. Journal of Paleontology 62 (3): 427-439.

Martindale, W. 1992. Calcified epibionts as palaeoecological tools: examples from the Recent and Pleistocene reefs of Barbados. Coral Reefs 11 (3): 167-177.

Tilbrook, K. J., P. J. Hayward & D. P. Gordon. 2001. Cheilostomatous Bryozoa from Vanuatu. Zoological Journal of the Linnean Society 131: 35-109.

Burrowing Beaky Amphipods

noreply@blogger.com (Christopher Taylor) — Mon, 03 Oct 2011 08:42:00 +0000

Oediceroides emarginatus, photographed by Gauthier Chapelle.

I've been out in the field for a couple of weeks, hence the momentary absence of regular posts. But I have returned, and shall kick off with a brief introduction to the Oedicerotidae.

The oedicerotids are another cluster within the systematic morass that is the gammaridean amphipods (other gammaridean families featured here and here). Members of the Oedicerotidae are marine benthic burrowing forms, appropriately solidly built (for an amphipod, at least), and most readily distinguished from most other gammarideans by their particularly long fifth pereiopods (the last pair of legs on the main body) (Barnard 1969). They also usually have a long peduncle on the third uropods (the 'tail' appendages), though one distinctive genus Metoediceros lacks the third uropod entirely (Barnard 1974). In many oedicerotids, the eyes have also moved upwards to become coalesced along the dorsal midline and the head often possesses a prominent rostrum. However, these features are absent from a number of Southern Hemisphere and deep-sea taxa (the latter of which generally lack eyes altogether).

Dorsal view of the head of Monoculodes borealis, showing the coalescent eyes, from Andrey Vedenin.

Oedicerotids of the genus Synchelidium have been shown to be predators of harpacticoid copepods (Yu & Suh 2006). The abundance of this food appears to determine their reproductive behaviour, as females produce larger broods in the spring when harpacticoids are more abundant than in the fall.

REFERENCES

Barnard, J. L. 1969. The families and genera of marine gammaridean Amphipoda. United States National Museum Bulletin 271: 1-535.

Barnard, J. L. 1974. Evolutionary patterns in gammaridean Amphipoda. Crustaceana 27 (2): 137-146.

Yu, O. H., & H.-L. Suh. 2006. Life history and reproduction of the amphipod Synchelidium trioostegitum (Crustacea, Oedicerotidae) on a sandy shore in Korea. Marine Biology 150: 141-148.

The Overall Scale

noreply@blogger.com (Christopher Taylor) — Tue, 13 Sep 2011 02:32:00 +0000

Scale insects have been the subjects of posts here twice before: in the first, I described their remarkable development, and in the second, I referred to the unusual genetics of some species. An appropriate next subject would, I suppose, be some of the ecological connections between scales and other animals.

Cochineal insects Dactylopius coccus on prickly pear, photographed by Joan Mundani.

Which starts, of course, with connections between scales and ourselves. Many scales are known as agricultural and horticultural pests, such as the red scale Aonidiella aurantii that attacks citrus. However, some scale species are not only welcomed but even deliberately cultivated due to commercial usage of the resins that they secrete. The two most significant commercial scales are the cochineal insects of the genus Dactylopius and the lac insect Kerria lacca. Other scale insects have also been used to produce similar products to those extracted from these species. Cochineal insects live on prickly pears, and produce carminic acid to ward off insect predators (though one predator, the caterpillar Laetilia coccidovora, is not only immune to the acid but stores it up to regurtitate at its own predators: Grimaldi & Engel 2005). Humans, on the other hand, are undeterred by carminic acid. The insects are collected, crushed, and the carminic acid extracted to produce the red dye cochineal, used (among other things) to give colour to food, or to dye fabric. It was an ill-fated attempt to establish a cochineal industry in Queensland that lead to the introduction of prickly pears to Australia: the plague-proportion spread of the prickly pears and their subsequent control by the moth Cactoblastis cactorum has become one of the textbook examples of biological pest control.

Branch covered with sticklac, produced by lac insects Kerria lacca, photographed by Jeffrey W. Lotz.

Lac insects produce a hard resinous shell for protection that, again, is their undoing in the eyes of humans. Sticklac, the twigs of trees covered by lac bugs, is harvested, then heated in canvas tubes. The resin melts and runs out through the canvas, leaving the wood and remaining insect parts behind. The resin is then processed to make the lacquer shellac. As a varnish, shellac has been mostly superseded by synthetic products, though it still has its afficionados. It is also used in the food industry to produce a shiny coating for confectionary or fruit.

Mating pair of the ant Acropyga epedana, photographed by Alex Wild. The queen is carrying the mealybug which while found the stockline for her new colony.

The use of scale products by humans has a long history. The Indian epic Mahabharata, believed written about the 8th century BC, describes the Lakshagriha, a highly flammable palace built by the Kaurava family out of shellac, jute and ghee in which they hoped to trap their enemies of the Pandava family (the Pandavas escaped through a tunnel when the palace burnt after having been warned by their uncle, though one wonders if the smell of ghee in the walls might have also aroused their suspicions). However, ants have been exploiting scale products for at least 40 million years, and probably much longer. Ants (like many other animals) are interested in scales for their honeydew, the excreted sugary waste from their sap diet. Ants not only collect the honeydew, they protect the scales from other insects and may carry them to fresher growth or more protected sites. Ants of the genus Acropyga are so dependent on mealybugs, waxy scale insects of the family Pseudococcidae, that when a young queen leaves her parent nest to mate, she will carry a mealybug with her so that her new colony can maintain its own stock. She even mates while holding on to it, as seen in the photo above. Acropyga queens have even been found preserved in Dominican amber, still carrying their mealybugs (Grimaldi & Engel 2005).

REFERENCE

Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press.

Gordians

noreply@blogger.com (Christopher Taylor) — Mon, 05 Sep 2011 08:14:00 +0000

Long-term followers of this site may recall this video, linked to over four years ago:

The animal emerging from the unfortunate cricket in the video is a Gordian or horsehair worm, Nematomorpha. Gordian worms spend most of their lives as internal parasites: either of insects (in the freshwater/terrestrial order Gordiida) or of shrimps and crabs (in the marine genus Nectonema). Of the two commonly used vernacular names for this group, 'Gordian worm' refers to the famed Gordian knot, and is derived from the appearance of mating tangles of these elongate animals. 'Horsehair worm' refers to the long-held belief (again, inspired by appearance) that the adult worms developed from horse hairs decaying in water. So persistent was this belief that Leidy felt compelled to report in 1870 on an attempt to generate horsehair worms by this method, explaining that, "I need hardly say that I looked at my horse-hairs for many months without having had the opportunity of seeing their vivification". He also scuttled the fear, which even Linnaeus had reported as fact, that a horsehair worm could inflict a nasty bite on anyone careless enough to handle one. In fact, Gordian worms (being internal parasites absorbing nutrients directly from the host when young and not feeding as adults) do not even possess a mouth. Instead, the males of many species possess a bifurcated tail end, used in copulation, that may have been mistaken for jaws. The complete absence of active feeding has the interesting side effect that adult Gordians may completely lack an internal bacterial flora (Hudson & Floate 2009).

Representative nematomorphs: Gordius (Gordiida) on the left and Nectonema on the right, from Biodidac.

The primary division within the Nematomorpha between the marine Nectonema and the terrestrial Gordiida is universally agreed upon. The two branches are ecologically, morphologically and molecularly divergent (Bleidorn et al. 2002). Adults of Nectonema have dorsal and ventral double rows of swimming bristles, while those of Gordiida lack bristles (except for, in some species, minute patches of bristles in front of the cloacal opening). Mature adults of Gordiida emerge from their insect host when the latter approaches or enters water. It has been suggested that the worm is able to cause its host to actively seek out water, but it seems more likely that the worm simply causes erratic but non-directional behaviour that may make the host more likely to come into contact with water than if it had remained in its preferred microhabitat (Thomas et al. 2002). Once the host does come close to water as a result of random movement, the worm may be able to induce a last suicidal jump; alternatively, it may simply be that the addled host does not recognise the water as dangerous and makes no attempt to avoid it.

Female Chordodes wrapped around a stick, laying a white egg string. Photo from the Hairworm Biodiversity Survey.

Once in the water, the adult Gordians will mate with any others present; when multiple adults emerge in close proximity, they may begin mating before they have even finished emerging from their host (Hanelt & Janovy 2004). The females lay their eggs in long strings: one female may lay nearly six million eggs, making them one of the potentially most fecund animals on the planet. The larvae that hatch from the eggs look nothing like their parents, being kind of sausage-shaped with an eversible, spiny proboscis. A larva will find itself an aquatic animal host such as an insect larva or mollusc to burrow into and form a cyst. If the aquatic secondary host is then eaten by a suitable terrestrial primary host (for instance, after an aquatic insect larva matures into a terrestrial adult), the cyst will hatch out and the Gordian will complete its development within the terrestrial host. The Gordian larva may also bypass the secondary host if a primary host drinks water containing Gordian larvae. The larva or mode of transmission of Nectonema remains unknown,but, as Nectonema adults live in the same habitat as their primary host, they probably do not require a secondary host.

Larva of Chordodes encased in a cyst, from the Hairworm Biodiversity Survey.

Phylogenetically, Gordians have usually been regarded as related to nematodes, with which they share a number of morphological features. However, a molecular analysis by Sørensen et al. (2008) suggested a relationship between Gordians and loriciferans (albeit with support that was not overwhelming). The Gordian larva (which has no equivalent in the direct-developing nematode life-cycle) does bear a vague resemblance to an adult loriciferan, though it is debatable whether the resemblance is more than superficial. Loriciferans have not appeared in many phylogenetic analyses to date, and further investigation is required to establish whether it is the adults or the larvae of the Gordians that hold the clues to their affinities.

REFERENCES

Bleidorn, C., A. Schmidt-Rhaesa & J. R. Garey. 2002. Systematic relationships of Nematomorpha based on molecular and morphological data. Invertebrate Biology 121 (4): 357-364.

Hanelt, B., & J. Janovy Jr. 2004. Untying a Gordian knot: the domestication and laboratory maintenance of a Gordian worm, Paragordius varius (Nematomorpha: Gordiida). Journal of Natural History 38: 939-950.

Hudson, A. J., & K. D. Floate. 2009. Further evidence for the absence of bacteria in horsehair worms (Nematomorpha: Gordiidae). Journal of Parasitology 95 (6): 1545-1547.

Leidy, J. 1870. The gordius, or hair-worm. The American Entomologist and Botanist 2 (7): 193-197.

Sørensen, M. V., M. B. Hebsgaard, I. Heiner, H. Glenner, E. Willerslev & R. M. Kristensen. 2008. New data from an enigmatic phylum: evidence from molecular sequence data supports a sister-group relationship between Loricifera and Nematomorpha. Journal of Zoological Systematics and Evolutionary Research 46 (3): 231-239.

Thomas, F., A. Schmidt-Rhaesa, G. Martin, C. Manu, P. Durand & F. Renaud. 2002. Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts? Journal of Evolutionary Biology 15 (3): 356-361.

Stars in the Pasture

noreply@blogger.com (Christopher Taylor) — Tue, 30 Aug 2011 03:21:00 +0000

Flowers of Stellaria graminea, photographed by Jiří Bohdal.

Last week, I described a situation where low morphological diversity disguised high chromosomal and species diversity. So it is fitting that, this week, I should be focusing on an almost opposite situation: high morphological and chromosomal diversity, but low species diversity.

Stellaria is a genus of weedy herbaceous plants native primarily to Northern Hemisphere temperate regions, though some species have been spread around the world by humans. Members of the genus are mostly characterised by deeply divided petals, so that at a glance a Stellaria flower may look to have twice as many petals as it really does. (It is notable in this regard, however, that Chinnappa & Morton (1984) recorded raising a single seedling of Stellaria longipes during breeding tests that produced flowers with entire rather divided petals, a feature generally characteristic of other related genera.) Up to about 200 species have been assigned to the genus (Bittrich 1993) but, considering what has been established with the American S. longipes complex (read on), I would not be at all surprised if that number is somewhat inflated. A review of Chinese Stellaria by Wu (1991), for instance, reduced a third of the species treated to synonyms.

Stellaria longipes, photographed by Michael Shepard.

The issue, as already alluded, is that some of the widespread Stellaria species are extremely variable. A case study of variability in Stellaria has been conducted with members of the Holarctic S. longipes complex (Macdonald et al. 1988). Four taxa are currently recognised within this group: Stellaria longipes ssp. longipes and S. longifolia both have circumpolar distributions in North America and Eurasia, but S. longipes ssp. arenicola and S. porsildii are each known from only small ranges in North America (Chinnappa 1992). Stellaria longifolia and S. porsildii are diploid species with a chromosome number of 26; S. longipes is a polyploid species, possibly derived from the hybridisation of the two diploids.

Specimens attributed to Stellaria longipes show a huge variation in morphological characters: stem pubescence, growth habit, floral and fruit characteristics, etc. They also show a wide variation in chromosome numbers: individuals have been recorded with as few as 51 or as many as 107 chromosomes. You may be thinking that such variation must indicate that a number of species have been conflated under the name of 'S. longipes', and, indeed, a number of names have been based on variant forms of this complex. However, breeding tests conducted by Chinnapa & Morton (1984) failed to find any reproductive isolation between different morphs: all were fully interfertile. What is more, different morphs are not found in different ranges, supporting the cultivation results as a valid representation of what is happening in the wild. Despite their variability in morphology, the representatives of S. longipes form a single, rampantly outbreeding gene pool. Even the apparent question of chromosome variability becomes less significant when one considers that the majority of individuals have chromosome numbers of 52, 78 or 104: all multiples of 26. If you compare this to what we find in Rhogeessa, you can see that it is not chromosome number alone that is the controlling factor for interfertility. The important thing is the ability or otherwise of the chromosomes to form associations during meiosis allowing their appropriate segregation to form viable gametes.

A slightly different form of Stellaria longipes, from here.

The only segregate of Stellaria longipes that appears to be truly distinct is the form known as S. longipes ssp. arenicola. This is a restricted range form known only from an area of sand dunes south of Lake Athabasca at the northern end of the border between Alberta and Saskatchewan (true S. longipes ssp. longipes is also found in the same area). Distinction appears to have arisen between S. l. ssp. longipes and S. l. ssp. arenicola as a result of a change in fertilisation regime for the latter. Stellaria species (including S. longipes) are mostly protandrous: the male parts of the flower mature before the female parts are ready to receive pollen. This means that a flower generally cannot fertilise itself, and individuals are generally outcrossing. Stellaria longipes ssp. arenicola has reversed this pattern: protandry is reduced, and individuals are more likely to be fertilised by themselves than by others. The nature of their sand dune habitat also means that plants are more likely to germinate successfully alongside another individual than in an isolated position. This results in a clumped and patchy distribution of individuals that also promotes fertilisation within a limited pool of individuals, as fertilising insects forage within a single patch rather than travelling between patches. Genetic analysis indicates that a limited amount of gene flow probably does still occur between sympatric S. longipes ssp. arenicola and S. l. ssp. longipes (Purdy et al. 1994); nevertheless, this outcrossing is on the order of the occasional dalliance rather than the shameless harlotry of their conspecifics elsewhere.

REFERENCES

Bittrich, V. 1993. Caryophyllaceae. In: Kubitzki, K., J. G. Rohwer & V. Bittrich (eds) The Families and Genera of Flowering Plants vol. 2. Flowering Plants: Dicotyledons: Magnoliid, hamamelid and caryophyllid families pp. 206-236. Springer.

Chinnappa, C. C. 1992. Stellaria porsildii, sp. nov., a new member of the S. longipes complex (Caryophyllaceae). Systematic Botany 17 (1): 29-32.

Chinnappa, C. C., & J. K. Morton. 1984. Studies on the Stellaria longipes complex (Caryophyllaceae)-biosystematics. Systematic Botany 9 (1): 60-73.

Macdonald, S. E., C. C. Chinnappa & D. M. Reid. 1988. Evolution of phenotypic plasticity in the Stellaria longipes complex: comparisons among cytotypes and habitats. Evolution 42 (5): 1036-1046.

Purdy, B. G., R. J. Bayer & S. E. Macdonald. 1994. Genetic variation, breeding system evolution, and conservation of the narrow sand dune endemic Stellaria arenicola and the widespread S. longipes (Caryophyllaceae). American Journal of Botany 81 (7): 904-911.

Wu Z.-Y. 1991. Some problems on the taxonomy of Chinese Stellaria. Acta Botanica Yunnanica 13 (4): 351-368.