Phylogeography and trans‐Pacific divergence of the rocky shore gastropod Nucella lima

AbstractAimWe have used phylogeographical and multilocus coalescent population genetic methods to reconstruct the Pleistocene biogeographical history of a broadly distributed north Pacific rocky shore gastropod, Nucella lima.LocationNorthern Pacific rim, from south‐eastern Alaska to Hokkaido Island.MethodsWe gathered DNA sequence data from three loci from N. lima, whose current distribution spans the entire North Pacific rim. We used a combination of population genetic summary statistics (Tajima's D, Fu's FS and ΦST), isolation‐with‐migration divergence models, and extended Bayesian skyline plots to reconstruct the recent biogeographical history of this species.ResultsThe largest values of ΦST across all loci were always between eastern and western samples. Population divergence models indicated no gene flow and mid‐Pleistocene divergence times (> 600 ka) between eastern and western populations. Mitochondrial DNA diversity in the east was low, and coalescent‐based estimates of effective population size were significantly smaller in the east 20,000 years ago, at the end of the last glacial period.Main conclusionsThe results are consistent with a hypothesis in which north Pacific populations were separated into eastern and western refugia by 317 ka with no gene flow since the split. Eastern populations probably underwent a severe bottleneck in population size during the last glacial period. The contrasting demographic histories of eastern and western populations are consistent with the general palaeobiogeographical pattern of greater climate‐related extinction of marine taxa in the eastern Pacific.