Genetic structure and population connectivity of Peltospira smaragdina along the north MAR: a next-generation sequencing approach

Resilience capacities of hydrothermal vent species are largely dependent on their dispersal abilities. Characterizing gene flow and identifying biotic and/or abiotic factors impacting population exchanges are thus of prime importance. In this study we focused on Peltospira smaragdina, a gastropod species inhabiting hydrothermal vent chimneys along the Mid-Atlantic Ridge (MAR). We genotyped 237 individuals from 6 hydrothermal fields (23°N to 45°N) at 12 522 SNPs using a double-digest restriction-site associated DNA sequencing (ddRAD). Using population genetics clustering approaches, three genetic groups were detected. These groups corresponded to the Moytirra vent field, fields of the Azorean triple junction, and the deeper sites of TAG, Snake-Pit and Broken-Spur. Fst values were in accordance with such results. Half of the individuals of Rainbow were however more related to the third and most southern group. Ancestry coefficient confirmed local admixture between the Lucky-Strike and TAG/Snake-Pit/Broken-Spur genetic clusters at Rainbow. These results indicated that (1) gene flow is greatly impeded between Moytirra and the other fields sampled, (2) TAG, Snake-Pit and Broken-Spur may be panmictic, and (3) the Rainbow field may represent a putative ‘hybrid’ zone receiving migrants from TAG/Snake-Pit/Broken-Spur at a rather low rate. Several hypotheses might explain genetic breaks between vent fields, such as the presence of topographical barriers (fracture zones) or decreasing depth near to the Azorean Triple Junction. Genetic differences observed along the MAR between Peltospira smaragdina and other species highlighted the need of performing comparative studies on several species having contrasted life-history traits, as planned in the iAtlantic WP1.