Population Structure and Diversity of Polynoids Associated with Tubeworms at Axial Seamount

Abstract

Polynoid worms at Axial Seamount represent a sizable portion of the already annelid dominant environment but have comparatively little work examining the population structure of the taxa. This study examined polynoid diversity and population structuring specifically associated with Ridgeia piscesae within the Caldera. Individual worms were sampled from three sites across the seamount, including the Inferno Chimney and a site of diffuse flow within the ASHES vent field and from the El Guapo Chimney within the International District field. DNA was extracted from the elytra of the Polynoids and sequenced using Restriction Site-Associated DNA sequencing to subsample a significant portion of the genome. Analysis of heterozygosity and Fis, (the inbreeding coefficient), revealed that high diversity and a low degree of inbreeding were present within the sample groups in contrast to what is observed in other deep-sea species. In addition, paired Fst analysis, Admixture, and DAPC all revealed little to no genetic differentiation between groups and that a high degree of shared ancestry was present across sites. This shared ancestry suggests that populations of Polynoids within the Caldera are panmictic and can be considered a single genetic population. This finding aligns with hypotheses of pseudo-copulatory reproduction in other deep-sea species as it allows for the copulatory mating behavior and internal fertilization proposed to still be present within the species dwelling in the Caldera while also allowing sufficient flexibility for the dispersal of propagules. This holds important implications for conserving deep-sea polynoids and presents a need for further research into their reproductive characteristics.