Looking beneath the tip of the iceberg: diversification of the genus Epimeria on the Antarctic shelf (Crustacea, Amphipoda)

The amphipod genus Epimeria is very speciose in Antarctic waters. Although their brooding biology, massive and heavily calcified body predict low dispersal capabilities, many Epimeria species are documented to have circum-Antarctic distributions. However, these distribution records are inevitably dependent on the morphological species definition. Yet, recent DNA evidence suggests that some of these Epimeria species may be complexes of species with restricted distributions. Mitochondrial COI and nuclear 28S rDNA sequence data were used to infer evolutionary relationships among 16 nominal Epimeria species from the Antarctic Peninsula, the eastern Weddell Sea and the Adélie Coast. Based on this phylogenetic framework, we used morphology and the DNA-based methods GMYC, bPTP and BPP to investigate species boundaries, in order to revise the diversity and distribution patterns within the genus. Most of the studied species appeared to be complexes of pseudocryptic species, presenting small and previously overlooked morphological differences. Altogether, 25 lineages were identified as putative new species, increasing twofold the actual number of Antarctic Epimeria species. Whereas most of the species may be geographically restricted to one of the three studied regions, some still have very wide distribution ranges, hence suggesting a potential for large-scale dispersal

DNA analyses reveal abundant homoplasy in taxonomically important morphological characters of Eusiroidea (Crustacea,Amphipoda)

Eusiroidea is one of the 20 amphipod superfamilies that were erected to subdivide the very large and controversial suborder Gammaridea. Yet, the definition of the superfamily is not based on synapomorphies, but on a combination of diagnostic phenetic similarities that hold more or less consistently across families. Moreover, many of the characters used to define eusiroid families are suspected to show convergent evolution. The current classification of the Eusiroidea may therefore not reflect evolutionary relationships accurately. Here, we present a molecular phylogenetic re-analysis of the Eusiroidea based on a comparison of 18S and 28S rDNA sequences of 73 species, representing 47 genera and 16 families that potentially belong to the superfamily. The results suggest that at least species belonging to 14 of these traditional families would be part of a eusiroid clade, increasing by more than twofold the species and generic richness of the group. However, most of the eusiroid families surveyed do not appear monophyletic. Finally, the analyses show that several important morphological characteristics, traditionally used in eusiroid taxonomy, are homoplastic

On the genus <i>Halirages</i> (Crustacea, Amphipoda), with the description of two new species from Scandinavia and Arctic Europe

A new common deep-sea species of Halirages Boeck, 1871 closely related to H. qvadridentatus G.O. Sars, 1877, H. cainae sp. nov., is described after specimens collected in the Norwegian Sea during the MAREANO 2009-111 cruise. Examination of the syntypes of H. elegans Norman, 1882 demonstrates that Norman’s species is a junior synonym of H. qvadridentatus G.O. Sars, 1877 and that the species usually named H. elegans in literature was actually undescribed. The name H. stappersi sp. nov. is proposed for that species. A key to and a checklist of Halirages species is given.</p

Genetic and Morphological Divergences in the Cosmopolitan Deep-Sea Amphipod Eurythenes gryllus Reveal a Diverse Abyss and a Bipolar Species

Eurythenes gryllus is one of the most widespread amphipod species, occurring in every ocean with a depth range covering the bathyal, abyssal and hadal zones. Previous studies, however, indicated the existence of several genetically and morphologically divergent lineages, questioning the assumption of its cosmopolitan and eurybathic distribution. For the first time, its genetic diversity was explored at the global scale (Arctic, Atlantic, Pacific and Southern oceans) by analyzing nuclear (28S rDNA) and mitochondrial (COI, 16S rDNA) sequence data using various species delimitation methods in a phylogeographic context. Nine putative species-level clades were identified within E. gryllus. A clear distinction was observed between samples collected at bathyal versus abyssal depths, with a genetic break occurring around 3,000 m. Two bathyal and two abyssal lineages showed a widespread distribution, while five other abyssal lineages each seemed to be restricted to a single ocean basin. The observed higher diversity in the abyss compared to the bathyal zone stands in contrast to the depth-differentiation hypothesis. Our results indicate that, despite the more uniform environment of the abyss and its presumed lack of obvious isolating barriers, abyssal populations might be more likely to show population differentiation and undergo speciation events than previously assumed. Potential factors influencing species’ origins and distributions, such as hydrostatic pressure, are discussed. In addition, morphological findings coincided with the molecular clades. Of all specimens available for examination, those of the bipolar bathyal clade seemed the most similar to the ‘true’ E. gryllus. We present the first molecular evidence for a bipolar distribution in a macro-benthic deep-sea organism

Statistical parsimony haplotype networks based on the 16S rDNA sequences of <i>Eurythenes gryllus</i>.

<p>The dataset includes sequences from this study, that of France and Kocher <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone.0074218-France2" target="_blank">[12]</a> and Escobar-Briones <i>et al. </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone.0074218-EscobarBriones1" target="_blank">[36]</a>. The area of each circle is proportional to the frequency of the haplotype in our sampling (a scale is presented). Each line represents a single substitution, nodes represent hypothetical haplotypes and colors refer to the sampling localities. Haplotype networks (95% probability threshold) are numbered (Eg1–9) according to the different clusters identified in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone-0074218-g002" target="_blank">Figures 2</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone-0074218-g003" target="_blank">3</a>.</p

Tree constructions on the three-gene dataset.

<p>Bayesian (BI) and Maximum Parsimony (MP) trees inferred for specimens of <i>Eurythenes gryllus</i> sampled in this study, based on the combined dataset of three genes (COI, 16S rDNA, 28S rDNA), showing posterior probabilities (>0.5) and bootstrap values (>50%; number of bootstrap replicates = 2,000), respectively. Two bootstrap values are shown at each node, the upper one represents the value when gaps were treated as fifth characters whilst the lower one represents the value when gaps were treated as missing data. The different clusters are assigned with the codes Eg1–5. For each cluster, distributional ranges (ocean basin, bathyal vs. abyssal, depth) are indicated. The colored squares refer to the sample localities of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone-0074218-g001" target="_blank">Figure 1</a>.</p

Sample localities of <i>Eurythenes gryllus sensu lato</i>.

<p>Abbreviations refer to samples from this study, that of France and Kocher <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone.0074218-France2" target="_blank">[12]</a> and Escobar-Briones <i>et al. </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone.0074218-EscobarBriones1" target="_blank">[36]</a> (for details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone-0074218-t001" target="_blank">Table 1</a>). The sampling region in the Southern Ocean is shown as an enlargement. Color codes are provided for each sampling locality and are used consistently in the other figures.</p

Results of the GMYC species delimitation test for <i>Eurythenes gryllus sensu lato</i> on the 16S dataset using single and multiple threshold methods.

<p>Statistical probabilities **P<0.01 and ***P<<0.0001.</p

Data of specimens of <i>Eurythenes gryllus sensu lato</i> (EG) and <i>Eurythenes</i> sp. (ES) obtained for this study and available on GenBank from France and Kocher [12] and Escobar-Briones <i>et al.</i>[36].

<p>For the specimens sequenced by France and Kocher <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone.0074218-France2" target="_blank">[12]</a>, the number of specimens is added between parentheses. Abbreviations: n.d. – no data, BT – baited traps, FT – fish traps.</p

Bayesian tree inferred for the 16S rDNA dataset of <i>Eurythenes gryllus</i>.

<p>Posterior probabilities (>0.5) are shown at each node. In the case of identical sequences, all specimens are listed with corresponding abbreviations. For the sequences retrieved from GenBank <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone.0074218-France2" target="_blank">[12]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074218#pone.0074218-EscobarBriones1" target="_blank">[36]</a>, the accession number of the haplotype as well as the number of specimens per haplotype is indicated (when higher than 1). The different clusters are assigned with the codes Eg1–9. For each cluster, distributional ranges (ocean basin, bathyal vs. abyssal, depth) are indicated.</p