Evolutionary history and biogeographical patterns of barnacles endemic to deep-sea hydrothermal vents

The characterization of evolutionary and biogeographical patterns is of fundamental importance to identify factors driving biodiversity. Due to their widespread but discontinuous distribution, deep-sea hydrothermal vent barnacles represent an excellent model for testing biogeographic hypotheses regarding the origin, dispersal, and diversity of modern vent fauna. Here we characterize the global genetic diversity of vent barnacles to infer their time of radiation, place of origin, mode of dispersal, and diversification. Our approach was to target a suite of multiple loci in samples representing seven out of the eight described genera. We also performed restriction-site associated DNA sequencing on individuals from each species. Phylogenetic inferences and topology hypothesis tests indicate that vent barnacles have colonized deep-sea hydrothermal vents at least twice in history. Consistent with preliminary estimates, we find a likely radiation of barnacles in vent ecosystems during the Cenozoic. Our analyses suggest that the western Pacific was the place of origin of the major vent barnacle lineage, followed by circumglobal colonization eastward through the southern hemisphere during the Neogene. The inferred time of radiation rejects classic hypotheses of antiquity of vent taxa. The timing and the mode of origin, radiation and dispersal are consistent with recent inferences made for other deep-sea taxa, including non-vent species, and are correlated with the occurrence of major geological events and mass extinctions. Thus, we suggest that the geological processes and dispersal mechanisms discussed here can explain current distribution patterns of many other marine taxa and have played an important role shaping deep-sea faunal diversity. These results also constitute critical baseline data with which to assess potential effects of anthropogenic disturbances on deep-sea ecosystems.