Phylogeny and biogeography of deep sea vestimentiferan tubeworms and their bacterial symbionts

The present study combines previously published morphological descriptions and molecular-based characterizations of vestimentiferans and their symbionts with new molecular data to summarize and extend the understanding of vestimentiferan host and symbiont phylogeny and biogeography. Host cytochrome oxidase I (COI) and symbiont 16S ribosomal gene (16S) DNA sequences were used to explore evolutionary relationships among the vestimentiferans and their symbionts. Lamellibrachids of the northern Gulf of Mexico (GOM) are identified as a single species, Lamellibrachia cf luymesi, and new data and analyses are presented for Lamellibrachia barhami, Paraescarpia echinospica, and Arcovestia ivanovi. In general, both vestimentiferan hosts and symbionts have very large species ranges that are interrupted by depth. No evidence for cospeciation was found between vestimentiferans and their symbionts, supporting an environmental acquisition of the symbionts. Symbiont acquisition depends on host type (vent or seep), depth of site, and possibly host species. A test of evolutionary rate showed that vent vestimentiferans had a significantly faster COI sequence evolution than lamellibrachids, and symbionts from vent and seep vestimentiferans from deep water sites had a significantly slower rate of evolution than those from mid-depth and shallow sites.