Gene Flow among Candidatus Endoriftia persephone Symbionts of Riftia pachyptila across Hydrothermal Vent Systems in the Guaymas Basin

Abstract

Deep-sea hydrothermal vents, which are commonly found along mid-ocean ridge systems and spreading centers in the deep ocean, are home to many endemic species of animals. While much of the deep sea is limited in primary production and readily available nutrients, mutualism between animal hosts and chemolithoautotrophic symbiotic bacteria is prevalent in hydrothermal vent systems, resulting in ecosystems which are brimming with life. Among the endemic species which can be found at hydrothermal vents is Riftia pachyptila, a siboglinid tubeworm species, which harbors the chemolithoautotrophic symbiotic bacterium, Candidatus Endoriftia persephone. Hydrothermal vents represent island-like habitats that are often hundreds to thousands of kilometers apart, and it is still poorly understood how vent populations are connected across these vast geographic distances. Understanding the genetic connectivity among organisms leads to insights about population tolerance to change, including anthropogenic activities, such as extractive deep-sea mining. Although previous research has explored the level of dispersal and genetic connectivity among animal species at hydrothermal vent systems, little is known about the movement and gene flow of symbionts across these systems. Further, this is the first study of genetic connectivity of Ca. E. persephone populations across hydrothermal vent systems in the Guaymas Basin. This study examined the level of gene flow across populations of Ca. E. persephone between distinct hydrothermal vent sites of the Guaymas Basin, Gulf of California, Mexico. Genetic diversity of Ca. E. persephone was investigated through metagenomic sequencing of the symbionts’ genomic DNA (gDNA). Symbiont populations were recovered from sixty-one R. pachyptila specimens collected from five hydrothermal vent sites across the Northern Trough and Southern Trough regions of the Guaymas Basin. Downstream population genomic analyses included examination of genetic variants and assessment of gene presence and absence. This study reports evidence of a high degree of Ca. E. persephone population connectivity across the Guaymas Basin. While further research is required to fully understand the drivers for this genetic homogeneity, these results do infer population stability and robustness.