The Belgica 121 expedition to the Western Antarctic Peninsula: a detailed biodiversity census.

BACKGROUND: This dataset relates to the biodiversity census carried out during the Belgica 121 (B121) expedition to the Western Antarctic Peninsula from February to March 2019. One of the aims of the campaign was to explore the surroundings of the Gerlache Strait and to carry out a detailed biodiversity census focusing on inter- and subtidal shallow-water areas using both classic descriptive marine ecology methods, as well as state-of-the art techniques (habitat mapping, genetics, trophic ecology). The biodiversity census was carried out onboard a nimble research vessel, RV Australis. This dataset will offer access to the raw data on biodiversity occurrences, obtained using a range of methods described in this data paper. NEW INFORMATION: New raw biodiversity data for a poorly-sampled region (Western Antarctic Peninsula) with a special focus on shallow ecosystems.

Not Frozen in the Ice: Large and Dynamic Rearrangements in the Mitochondrial Genomes of the Antarctic Fish.

The vertebrate mitochondrial genomes generally present a typical gene order. Exceptions are uncommon and important to study the genetic mechanisms of gene order rearrangements and their consequences on phylogenetic output and mitochondrial function. Antarctic notothenioid fish carry some peculiar rearrangements of the mitochondrial gene order. In this first systematic study of 28 species, we analyzed known and undescribed mitochondrial genome rearrangements for a total of eight different gene orders within the notothenioid fish. Our reconstructions suggest that transpositions, duplications, and inversion of multiple genes are the most likely mechanisms of rearrangement in notothenioid mitochondrial genomes. In Trematominae, we documented an extremely rare inversion of a large genomic segment of 5,300 bp that partially affected the gene compositional bias but not the phylogenetic output. The genomic region delimited by nad5 and trnF, close to the area of the Control Region, was identified as the hot spot of variation in Antarctic fish mitochondrial genomes. Analyzing the sequence of several intergenic spacers and mapping the arrangements on a newly generated phylogeny showed that the entire history of the Antarctic notothenioids is characterized by multiple, relatively rapid, events of disruption of the gene order. We hypothesized that a pre-existing genomic flexibility of the ancestor of the Antarctic notothenioids may have generated a precondition for gene order rearrangement, and the pressure of purifying selection could have worked for a rapid restoration of the mitochondrial functionality and compactness after each event of rearrangement.

Species integrity, introgression, and genetic variation across a coral reef fish hybrid zone.

Hybridization and introgression are evolutionarily significant phenomena breaking down species boundaries. "Hybrid zones" (regions of species overlap and hybridization) enable quantification of hybridization frequency and examination of mechanisms driving and maintaining gene flow. The hybrid anemonefish Amphiprion leucokranos is found where parent species (A. chrysopterus; A. sandaracinos) distributions overlap. Here, we examine geographic variation in hybridization and introgression, and potential impacts on parent species integrity through assessing relative abundance, social group composition, and genetic structure (mtDNA cytochrome b, 21 microsatellite loci) of taxa at three hybrid zone locations: Kimbe Bay (KB) and Kavieng (KA), Papua New Guinea; the Solomon Islands (SO). Relative abundances of and size disparities between parent species apparently drive hybridization frequency, introgression patterns, and genetic composition of taxa. Conspecific groups are most common in KB (65%) where parent species are similarly abundant. Conversely, mixed species groups dominate SO (82%), where A. chrysopterus is more abundant. Hybrids most commonly cohabit with A. sandaracinos in KB (17%), but with A. chrysopterus in KA (22%) and SO (50%). Genetic differentiation (nDNA) analyses indicate that parent species remain distinct, despite ongoing hybridization and hybrids are genetically similar to A. sandaracinos-resulting from persistent backcrossing with this smallest species. This study shows that hybridization outcomes may depend on the social and ecological context in which taxa hybridize, where relative abundance and disparate size of parent species explain the frequency and patterns of hybridization and introgression in the A. leucokranos hybrid zone, reflecting size-based dominance behaviors of anemonefish social groups.