P2.114 Tuesday, Jan. 5 Going all the way: Phylogeography and trans-Pacific divergence genetics of two rocky-shore snails COX, L.N.*; EMME, S.A.; ZASLAVSKAYA, N.I.; MARKO, P.B; Clemson University; Clemson University; Russian Academy of Sciences; Clemson University email@example.com
Although fluctuating climate over the last 2 million years (MY) repeatedly caused latitudinal shifts in species distributions, did the glacial-interglacial dynamics of the Pleistocene drive regional genetic differentiation and potentially speciation? For species whose distributions spanned the entire north Pacific, regional extinction of northern populations during cooler glacial periods may have resulted in isolation of eastern and western populations, potentially leading to trans-Pacific differentiation and speciation. To characterize patterns of east-west differentiation in rocky-shore species whose current (i.e. interglacial) distributions span the entire north Pacific, we have gathered genetic data from two intertidal gastropods, Nucella lima and Littorina sitkana. Although N. lima is present in Japan and Alaska, we failed to find it on the Kamchatka Peninsula, Sakhalin Island and the Sea of Okhotsk, suggesting a discontinuous distribution. MtDNA sequences from N. lima are reciprocally monophyletic with respect to eastern and western populations, suggesting an extended period of geographic isolation. In contrast, L. sitkana is continuously distributed across the entire North Pacific and lacks any obvious east-west mtDNA phylogeographic structure. Both species show a marked asymmetry in mtDNA diversity, with much higher sequence diversity in the west. To determine if differences in mtDNA genealogies actually reflect different population histories (rather than stochastic variation in gene tree coalescences), we have gathered data from several nuclear genes, which will presumably allow us to jointly estimate divergence times, gene flow, and effective population sizes between eastern and western populations with greater precision than mtDNA alone.