A pioneer morphological and genetic study of the intertidal fauna of the Gerlache Strait (Antarctic Peninsula).

The underexplored intertidal ecosystems of Antarctica are facing rapid changes in important environmental factors. Associated with temperature increase, reduction in coastal ice will soon expose new ice-free areas that will be colonized by local or distant biota. To enable detection of future changes in faunal composition, a biodiversity baseline is urgently required. Here, we evaluated intertidal faunal diversity at 13 locations around the Gerlache Strait (western Antarctic Peninsula), using a combination of a quadrat approach, morphological identification and genetic characterization. Our data highlight a community structure comprising four generally distributed and highly abundant species (the flatworm Obrimoposthia wandeli, the bivalve Kidderia subquadrata, and the gastropods Laevilitorina umbilicata and Laevilitorina caliginosa) as well as 79 rarer and less widely encountered species. The most abundant species thrive in the intertidal zone due to their ability to either survive overwinter in situ or to rapidly colonize this zone when conditions allow. In addition, we confirmed the presence of multiple trophic levels at nearly all locations, suggesting that complex inter-specific interactions occur within these communities. Diversity indices contrasted between sampling locations (from 3 to 32 species) and multivariate approaches identified three main groups. This confirms the importance of environmental heterogeneity in shaping diversity patterns within the investigated area. Finally, we provide the first genetic and photographic baseline of the Antarctic intertidal fauna (106 sequences, 137 macrophotographs), as well as preliminary insights on the biogeography of several species. Taken together, these results provide a timely catalyst to assess the diversity and to inform studies of the potential resilience of these intertidal communities.

Facilitating population genomics of non-model organisms through optimized experimental design for reduced representation sequencing.

BACKGROUND: Genome-wide data are invaluable to characterize differentiation and adaptation of natural populations. Reduced representation sequencing (RRS) subsamples a genome repeatedly across many individuals. However, RRS requires careful optimization and fine-tuning to deliver high marker density while being cost-efficient. The number of genomic fragments created through restriction enzyme digestion and the sequencing library setup must match to achieve sufficient sequencing coverage per locus. Here, we present a workflow based on published information and computational and experimental procedures to investigate and streamline the applicability of RRS. RESULTS: In an iterative process genome size estimates, restriction enzymes and size selection windows were tested and scaled in six classes of Antarctic animals (Ostracoda, Malacostraca, Bivalvia, Asteroidea, Actinopterygii, Aves). Achieving high marker density would be expensive in amphipods, the malacostracan target taxon, due to the large genome size. We propose alternative approaches such as mitogenome or target capture sequencing for this group. Pilot libraries were sequenced for all other target taxa. Ostracods, bivalves, sea stars, and fish showed overall good coverage and marker numbers for downstream population genomic analyses. In contrast, the bird test library produced low coverage and few polymorphic loci, likely due to degraded DNA. CONCLUSIONS: Prior testing and optimization are important to identify which groups are amenable for RRS and where alternative methods may currently offer better cost-benefit ratios. The steps outlined here are easy to follow for other non-model taxa with little genomic resources, thus stimulating efficient resource use for the many pressing research questions in molecular ecology.

Locked in the icehouse: Evolution of an endemic Epimeria (Amphipoda, Crustacea) species flock on the Antarctic shelf.

The Antarctic shelf's marine biodiversity has been greatly influenced by the climatic and glacial history of the region. Extreme temperature changes led to the extinction of some lineages, while others adapted and flourished. The amphipod genus Epimeria is an example of the latter, being particularly diverse in the Antarctic region. By reconstructing a time-calibrated phylogeny based on mitochondrial (COI) and nuclear (28S and H3) markers and including Epimeria species from all oceans, this study provides a temporal and geographical framework for the evolution of Antarctic Epimeria. The monophyly of this genus is not supported by Bayesian Inference, as Antarctic and non-Antarctic Epimeria form two distinct well-supported clades, with Antarctic Epimeria being a sister clade to two stilipedid species. The monophyly of Antarctic Epimeria suggests that this clade evolved in isolation since its origin. While the precise timing of this origin remains unclear, it is inferred that the Antarctic lineage arose from a late Gondwanan ancestor and hence did not colonize the Antarctic region after the continent broke apart from the other fragments of Gondwanaland. The initial diversification of the clade occurred 38.04Ma (95% HPD [48.46Ma; 28.36Ma]) in a cooling environment. Adaptation to cold waters, along with the extinction of cold-intolerant taxa and resulting ecological opportunities, likely led to the successful diversification of Epimeria on the Antarctic shelf. However, there was neither evidence of a rapid lineage diversification early in the clade's history, nor of any shifts in diversification rates induced by glacial cycles. This suggests that a high turnover rate on the repeatedly scoured Antarctic shelf could have masked potential signals of diversification bursts.

Detection and characterisation of mutations responsible for allele-specific protein thermostabilities at the Mn-superoxide dismutase gene in the deep-sea hydrothermal vent polychaete Alvinella pompejana.

Alvinella pompejana (Polychaeta, Alvinellidae) is one of the most thermotolerant marine eukaryotes known to date. It inhabits chimney walls of deep-sea hydrothermal vents along the East Pacific Rise (EPR) and is exposed to various challenging conditions (e.g. high temperature, hypoxia and the presence of sulphides, heavy metals and radiations), which increase the production of dangerous reactive oxygen species (ROS). Two different allelic forms of a manganese-superoxide dismutase involved in ROS detoxification, ApMnSOD1 and ApMnSOD2, and differing only by two substitutions (M110L and A138G) were identified in an A. pompejana cDNA library. RFLP screening of 60 individuals from different localities along the EPR showed that ApMnSOD2 was rare (2 %) and only found in the heterozygous state. Dynamic light scattering measurements and residual enzymatic activity experiments showed that the most frequent form (ApMnSOD1) was the most resistant to temperature. Their half-lives were similarly long at 65 °C (>110 min) but exhibited a twofold difference at 80 °C (20.8 vs 9.8 min). Those properties are likely to be explained by the occurrence of an additional sulphur-containing hydrogen bond involving the M110 residue and the effect of the A138 residue on the backbone entropy. Our results confirm the thermophily of A. pompejana and suggest that this locus is a good model to study how the extreme thermal heterogeneity of the vent conditions may help to maintain old rare variants in those populations.

Balanced Polymorphism at the Pgm-1 Locus of the Pompeii Worm Alvinella pompejana and Its Variant Adaptability Is Only Governed by Two QE Mutations at Linked Sites.

The polychaete Alvinella pompejana lives exclusively on the walls of deep-sea hydrothermal chimneys along the East Pacific Rise (EPR), and displays specific adaptations to withstand the high temperatures and hypoxia associated with this highly variable habitat. Previous studies have revealed the existence of a balanced polymorphism on the enzyme phosphoglucomutase associated with thermal variations, where allozymes 90 and 100 exhibit different optimal activities and thermostabilities. Exploration of the mutational landscape of phosphoglucomutase 1 revealed the maintenance of four highly divergent allelic lineages encoding the three most frequent electromorphs over the geographic range of A. pompejana. This polymorphism is only governed by two linked amino acid replacements, located in exon 3 (E155Q and E190Q). A two-niche model of selection, including 'cold' and 'hot' conditions, represents the most likely scenario for the long-term persistence of these isoforms. Using directed mutagenesis and the expression of the three recombinant variants allowed us to test the additive effect of these two mutations on the biochemical properties of this enzyme. Our results are coherent with those previously obtained from native proteins, and reveal a thermodynamic trade-off between protein thermostability and catalysis, which is likely to have maintained these functional phenotypes prior to the geographic separation of populations across the Equator about 1.2 million years ago.

Epimeria cleo sp. nov., a new crested amphipod from the Ross Sea, Antarctica, with notes on its phylogenetic affinities (Crustacea, Amphipoda, Eusiroidea, Epimeriidae).

A new crested amphipod, Epimeria cleo sp. nov., is described after specimens collected in the western Ross Sea, Southern Ocean, at 151-409 m depth. This increases the number of Epimeria species known from the Ross Sea to eleven. This new species belongs to the subgenus Drakepimeria d'Udekem d'Acoz Verheye, 2017. E. cleo sp. nov. has very robust walking pereiopods, no mid-dorsal tooth or bump on pereonites 1-2, no lateral tooth or angle on the lateral carina of coxa 4 and no pair of small teeth pointing upwards on urosomite 2. It is morphologically very similar to Epimeria leukhoplites d'Udekem d'Acoz Verheye, 2017, E. reoproi Lörz Coleman, 2001 and E. vaderi Coleman, 1998, the latter three species being known only from the Antarctic Peninsula and South Shetland Islands. Epimeria cleo sp. nov. can be distinguished from them by the following combination of characters: flexed rostrum, narrow coxa 3, long ventral tooth on coxa 4 and non-duplicate lateral tooth on pleonites 1-2. The phylogenetic relationships between E. cleo sp. nov. and other Epimeria of the subgenus Drakepimeria, for which DNA sequences are available, are briefly outlined based on a phylogenetic analysis of 28S rDNA fragments.