We have developed a bioinformatics pipeline for the comparative evolutionary analysis of Ensembl genomes, and have used it to analyse the introns of the five available teleost fish genomes. We show our pipeline to be a powerful tool for revealing variation between genomes that may otherwise be overlooked with simple summary statistics. We identify that the zebrafish, Danio rerio, has an unusual distribution of intron sizes, with a greater number of larger introns in general and a notable peak in the frequency of introns of ∼500 bp to 2,000 bp compared to the monotonically decreasing frequency distributions of the other fish. We determine that 47% of Danio rerio introns are composed of repetitive sequences, although the remainder, over 331 Mb, is not. Since repetitive elements may be the origin of the majority of all non-coding DNA, it is likely that the remaining Danio rerio intronic sequence has an ancient repetitive origin and has since accumulated so many mutations that it can no longer be recognised as such. To study such an ancient expansion of repeats in the Danio lineage will require further comparative analysis of fish genomes incorporating a broader distribution of teleost lineages.

In order to examine the physiological capabilities of marine invertebrates in their natural environment, a series of physiological measurements were conducted on congeneric amphipod species (Genus Gammarus) distributed along a natural thermal gradient in the NE Atlantic and Arctic Oceans. This synoptic paper summarises our most recent findings by describing physiological differences within and between Gammarus species collected from the intertidal between Portugal at 38N and Svalbard at 79N. Two physiological variables were examined to include temperature-adaptive responses at two different levels of biological organisation: (1) whole animal responses by measuring oxygen uptake rates as a measure of metabolic rates or costs of living; and (2) molecular responses by examining sequence variation in two functional regions of the myosin heavy chain gene (loops 1 and 2) which influence muscle contractibility. Our initial observations on Gammarus species showed that physiological variation as a function of latitude was species-specific. For instance, the sub-arctic/boreal species Gammarus oceanicus did not compensate its metabolism at polar latitudes. Instead, metabolic rates declined with latitudinal changes in temperature resulting in relatively low rates of metabolism in the sub-arctic population. In contrast, the boreal and temperate species G. locusta and G. duebeni duebeni conserved metabolic rate across latitudes indicating a capacity for physiological compensation. A similar response was observed at the molecular level as sequence diversity in the loop 2 region of the myosin heavy chain gene remained unchanged with latitude in G. oceanicus but increased with latitude in G. d. duebeni which was attributed to differences in thermal habitat. Further work is required to establish whether these physiological differences involve local adaptation or are dependent on phenotypic plasticity. These findings provide valuable information on the ability of each species to adjust their physiology to maintain function despite increases in temperature due to global warming.

Through adaptive radiation, ancestral species rapidly diversify into multiple species with different ecological adaptations. The haplochromine cichlid fishes of the East African Great Lakes are considered classic examples of adaptive radiation, but our understanding of the evolutionary origins of these radiations has been limited by inadequate taxonomic and genomic sampling [1,2]. Perhaps the largest of these radiations is from Lake Malawi, estimated to contain between 500 and 800 endemic species. Surprisingly, its monophyly – the origin from a single ancestral species – has never been critically tested. This is because river populations which could have seeded the radiation, with one very limited exception [3], have never been included in phylogenetic reconstructions. Moreover, phylogenies have relied heavily on mitochondrial DNA (mtDNA), which can be a misleading phylogenetic marker for species capable of hybridization [4,5] because its non-recombining nature means that transfer to other species can occur via asymmetric introgression and ‘allele surfing’[6]. Here, we used broad taxonomic sampling and nuclear DNA markers with wide genomic coverage and find that the Lake Malawi radiation is not monophyletic, but instead contains genetic material from divergent riverine ancestors indicating multiple invasions and hybridization.

Background: Nematodes represent the most abundant benthic metazoa in one of the largest habitats on earth, the deep sea. Characterizing major patterns of biodiversity within this dominant group is a critical step towards understanding evolutionary patterns across this vast ecosystem. The present study has aimed to place deep-sea nematode species into a phylogenetic framework, investigate relationships between shallow water and deep-sea taxa, and elucidate phylogeographic patterns amongst the deep-sea fauna.

Results: Molecular data (18 S and 28 S rRNA) confirms a high diversity amongst deep-sea Enoplids. There is no evidence for endemic deep-sea lineages in Maximum Likelihood or Bayesian phylogenies, and Enoplids do not cluster according to depth or geographic location. Tree topologies suggest frequent interchanges between deep-sea and shallow water habitats, as well as a mixture of early radiations and more recently derived lineages amongst deep-sea taxa. This study also provides convincing evidence of cosmopolitan marine species, recovering a subset of Oncholaimid nematodes with identical gene sequences (18 S, 28 S and cox1) at trans-Atlantic sample sites.

Conclusions: The complex clade structures recovered within the Enoplida support a high global species richness for marine nematodes, with phylogeographic patterns suggesting the existence of closely related, globally distributed species complexes in the deep sea. True cosmopolitan species may additionally exist within this group, potentially driven by specific life history traits of Enoplids. Although this investigation aimed to intensively sample nematodes from the order Enoplida, specimens were only identified down to genus (at best) and our sampling regime focused on an infinitesimal small fraction of the deep-sea floor. Future nematode studies should incorporate an extended sample set covering a wide depth range (shelf, bathyal, and abyssal sites), utilize additional genetic loci (e.g. mtDNA) that are informative at the species level, and apply high-throughput sequencing methods to fully assay community diversity. Finally, further molecular studies are needed to determine whether phylogeographic patterns observed in Enoplids are common across other ubiquitous marine groups (e.g. Chromadorida, Monhysterida).

Background: The subclass Enoplia (Phylum Nematoda) is purported to be the earliest branching clade amongst all nematode taxa, yet the deep phylogeny of this important lineage remains elusive. Free-living marine species within the order Enoplida play prominent roles in marine ecosystems, but previous molecular phylogenies have provided only the briefest evolutionary insights; this study aimed to firmly resolve internal relationships within the hyper-diverse but poorly understood Enoplida. In addition, we revisited the molecular framework of the Nematoda using a rigorous phylogenetic approach in order to investigate patterns of early splits amongst the oldest lineages (Dorylaimia and Enoplia).

Results: Morphological identifications, nuclear gene sequences (18S and 28S rRNA), and mitochondrial gene sequences (cox1) were obtained from marine Enoplid specimens representing 37 genera. The 18S gene was used to resolve deep splits within the Enoplia and evaluate the branching order of major clades in the nematode tree; multiple phylogenetic methods and rigorous empirical tests were carried out to assess tree topologies under different parameters and combinations of taxa. Significantly increased taxon sampling within the Enoplida resulted in a well-supported, robust phylogenetic topology of this group, although the placement of certain clades was not fully resolved. Our analysis could not unequivocally confirm the earliest splits in the nematode tree, and outgroup choice significantly affected the observed branching order of the Dorylaimia and Enoplia. Both 28S and cox1 were too variable to infer deep phylogeny, but provided additional insight at lower taxonomic levels.

Conclusions: Analysis of internal relationships reveals that the Enoplia is split into two main clades, with groups consisting of terrestrial (Triplonchida) and primarily marine fauna (Enoplida). Five independent lineages were recovered within the Enoplida, containing a mixture of marine and terrestrial species; clade structure suggests that habitat transitions have occurred at least four times within this group. Unfortunately, we were unable to obtain a consistent or well-supported topology amongst early-branching nematode lineages. It appears unlikely that single-gene phylogenies using the conserved 18S gene will be useful for confirming the branching order at the base of the nematode tree–future efforts will require multi-gene analyses or phylogenomic methods.

The genus Gammarus (Amphipoda) is one of the most speciose genera of Crustacea, yet much uncertainty remains concerning taxonomy and systematic relationships, particularly for brackish and marine forms. We used DNA barcode sequences from the mitochondrial cytochrome c oxidase I (COI) gene to probe the taxonomy of prominent members of marine and brackish water Gammarus of the North Atlantic, Baltic, Mediterranean and Black Seas. We investigated 16 putative Gammarus spp. at an average number of 9 specimens per species. This constitutes the most taxonomically and geographically comprehensive molecular study of marine Gammarus to date. Average between-species sequence divergence (26.8%) was much higher than intraspecific distances (0.8%), enabling clear molecular species identification and highlighting several possible misidentifications from previously published studies. Specimens of Gammarus aequicauda and G. insensibilis from the Black Sea were at least 14% distant from their putative conspecifics elsewhere. Placing these findings in a geographic context provides strong indication of cryptic speciation. Further, we detected phylogeographic splits in G. oceanicus and G. duebeni. Our analyses also suggest phylogenetic positioning of G. marinus with members of the genus Echinogammarus, thus confirming its classification as Echinogammarus marinus. We have demonstrated that comprehensive analyses of taxonomically complex groups using DNA barcodes can result in a diversity of complementary data on taxonomy, phylogeography and phylogenetics. The combination of these results, with further morphological and ecological data, will enable significant progress in our understanding of this ecologically important group of crustaceans.