Phylogenetic divergence and population genetics of the hydrothermal vent annelid genus Hesiolyra along the East Pacific Rise: Reappraisal using multi-locus data

Aim: Maintaining genetic connectivity is crucial for species that inhabit the disjunct and unstable deep-sea hydrothermal vents. We aimed to re-assess the connectivity of the annelid genus Hesiolyra distributed at hydrothermal vents along the East Pacific Rise (EPR). A previous study detected a major clade among five Hesiolyra populations spanning from 13°N to 21°S and a minor sympatric southern clade with ~1% divergence from the major clade. However, this study was based on a short locus of 366-bp COI gene, which might not contain sufficient informative sites.

Location: East Pacific Rise.

Methods: We sequenced 188 specimens of Hesiolyra from five hydrothermal vent fields along the East Pacific Rise for six mitochondrial and two nuclear loci to infer their genetic divergence, population diversity and gene flow.

Results: We found a minor southern clade (Hesiolyra aff. bergi) which was genetically distinct from Hesiolyra bergi sensu stricto for all gene markers explored except 16S. We also found shared genotypes between H. bergi and H. aff. bergi likely resulted from incomplete lineage sorting. For H. bergi s.s., we found a low but fixed divergence between the north and south EPR populations. We estimated the northern and southern metapopulations of H. bergi s.s. split ~0.45 Mya (HPD: 0.27–0.74 Mya). The northern metapopulation had a higher haplotype diversity than the southern metapopulation, indicating historical gene flow and loss of genetic diversity in the southern clade.

Main conclusions: We confirmed that the equatorial dispersal filter observed previously on several other vent species also applies to H. bergi. Our results highlight the power of the multi-locus approach in revealing the divergence and population genetic history of marine species with strong dispersal capabilities, indicating that the NEPR and the SEPR should be considered as separate biogeographic regions in environmental management and biological conservation.