Connectivity study of hydrothermal vent gastropods

To date, more than 30 gastropod species live in the vent fields along the Central and Southeast Indian Ridge and all of them are assumed to be vent-related. During the INDEX project, 425 representatives of the genus Anatoma (Mollusca: Vetigastropoda) were sampled in six abyssal hydrothermal vent areas. In a previous study, a high genetic similarity was found between A. paucisculpta and an undescribed anatomid sampled from a hydrothermal vent field in the Lau Basin in the southern Pacific Ocean indicating a vent-related condition. For the first time, traditional morphology was combined with COI barcoding and 2b-RAD sequencing to study community structure and connectivity between the different vent fields. As a result, 2b-RAD sequencing confirmed the primary species hypothesis for 125 individuals of the recently-described taxa A. discapex, A. declivis, A. laevapex and A. paucisculpta. A subset of 22 additional specimens were solely determined by 2b-RAD sequencing and the updated community analyses confirmed the pattern of expanding populations. Investigating the population structure and FST-values is indicating a high connectivity along the six sampled vent fields for the three most abundant species. High levels of breeding and gene flow are suggested, pointing to good dispersal strategies of the target species along the studied area. Nevertheless, low number of heterozygosity reveals a small gene pool and therefore an increased vulnerability towards environmental changes. Our results showed that 2b-RAD sequencing, combined with other molecular methods, can accurately characterize macrobenthic mollusc communities. The sequencing technology constitutes an essential tool for continued monitoring. We also highlight that inferred molecular/ecological patterns provide important insights into hydrothermal vent ecosystems, which are essential in successful conservation and management programs.