Atlantic bonito (Sarda) genomic analysis reveals population differentiation across Northeast Atlantic and mediterranean locations: Implications for fishery management.

The Atlantic bonito (Sarda, family Scombridae) is a pelagic species and one of the most exploited small tuna species. Despite its economic importance, biological information is scarce with no associated management directives. In this study, using a population genomic approach resulted in a lack of panmixia of two genetic pools with different effective population sizes (east central-tropical Atlantic and northeast Atlantic-Mediterranean) and an intermixing zone in Atlantic Morocco. The absence of genetic heterogeneity between the locations in Atlantic - Mediterranean transitional zone adds new evidence that challenges the Strait of Gibraltar as a phylogeographic barrier for marine pelagic species. These results are proposed to the ICCAT Commission to establish management areas for this species, although they are not consistent with the recently adopted pelagic ecoregions. Finally, a panel of highly informative SNPs was developed for efficient and low-cost population assignment and the analysis of unresolved population structures.

Not out of the Mediterranean: Atlantic populations of the gorgonian Paramuricea clavata are a separate sister species under further lineage diversification.

The accurate delimitation of species boundaries in nonbilaterian marine taxa is notoriously difficult, with consequences for many studies in ecology and evolution. Anthozoans are a diverse group of key structural organisms worldwide, but the lack of reliable morphological characters and informative genetic markers hampers our ability to understand species diversification. We investigated population differentiation and species limits in Atlantic (Iberian Peninsula) and Mediterranean lineages of the octocoral genus Paramuricea previously identified as P. clavata. We used a diverse set of molecular markers (microsatellites, RNA-seq derived single-copy orthologues [SCO] and mt-mutS [mitochondrial barcode]) at 49 locations. Clear segregation of Atlantic and Mediterranean lineages was found with all markers. Species-tree estimations based on SCO strongly supported these two clades as distinct, recently diverged sister species with incomplete lineage sorting, P. cf. grayi and P. clavata, respectively. Furthermore, a second putative (or ongoing) speciation event was detected in the Atlantic between two P. cf. grayi color morphotypes (yellow and purple) using SCO and supported by microsatellites. While segregating P. cf. grayi lineages showed considerable geographic structure, dominating circalittoral communities in southern (yellow) and western (purple) Portugal, their occurrence in sympatry at some localities suggests a degree of reproductive isolation. Overall, our results show that previous molecular and morphological studies have underestimated species diversity in Paramuricea occurring in the Iberian Peninsula, which has important implications for conservation planning. Finally, our findings validate the usefulness of phylotranscriptomics for resolving evolutionary relationships in octocorals.

Genetic hypervariability of a Northeastern Atlantic venomous rockfish.

BACKGROUND: Understanding the interplay between climate and current and historical factors shaping genetic diversity is pivotal to infer changes in marine species range and communities' composition. A phylogeographical break between the Atlantic and the Mediterranean has been documented for several marine organisms, translating into limited dispersal between the two basins. METHODS: In this study, we screened the intraspecific diversity of 150 individuals of the Madeira rockfish (Scorpaena maderensis) across its distributional range (seven sampling locations in the Atlantic and Mediterranean basins) using the mitochondrial control region and the nuclear S7 first intron. RESULTS: The present work is the most comprehensive study done for this species, yielding no genetic structure across sampled locations and no detectable Atlantic-Mediterranean break in connectivity. Our results reveal deep and hyper-diverse bush-like genealogies with large numbers of singletons and very few shared haplotypes. The genetic hyper-diversity found for the Madeira rockfish is relatively uncommon in rocky coastal species, whose dispersal capability is limited by local oceanographic patterns. The effect of climate warming on the distribution of the species is discussed.

Insights into the genetic structure of the rabbitfish Chimaera monstrosa (Holocephali) across the Atlantic-Mediterranean transition zone.

A comparison of the genetic structure of Chimaera monstrosa populations from the Atlantic Ocean and the Mediterranean Sea was carried out using mitochondrial DNA analysis. Results indicate high and significant pairwise ΦST values with no shared haplotypes between the two areas. Furthermore, migration rate estimates suggested absence of gene flow between the two basins. These findings, coupled with the species vertical distribution, suggest that the shallow depth of the Strait of Gibraltar may act as a barrier limiting the dispersal capabilities of these populations, which likely became separated at the end of the middle Pleistocene.