Phylogeography and trans‐Pacific divergence of the rocky shore gastropod <i>Nucella lima</i>

Abstract

Abstract Aim We have used phylogeographical and multilocus coalescent population genetic methods to reconstruct the Pleistocene biogeographical history of a broadly distributed north P acific rocky shore gastropod, N ucella lima . Location Northern Pacific rim, from south‐eastern A laska to H okkaido I sland. Methods We gathered DNA sequence data from three loci from N . lima , whose current distribution spans the entire N orth P acific rim. We used a combination of population genetic summary statistics ( T ajima's D , F u's F S and Φ ST ), isolation‐with‐migration divergence models, and extended Bayesian skyline plots to reconstruct the recent biogeographical history of this species. Results The largest values of Φ ST across all loci were always between eastern and western samples. Population divergence models indicated no gene flow and mid‐ P leistocene divergence times (&gt; 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 conclusions The results are consistent with a hypothesis in which north P acific 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 P acific.