Meeting Abstract

11.1  Sunday, Jan. 4  Trans-Pacific phylogeography: geographic isolation and speciation in Nucella lima COX, L.N.*; MARKO, P.B.; Clemson University; Clemson University lncox@clemson.edu

Fluctuating climate during the last 2 million years (MY) repeatedly caused latitudinal shifts and fragmentation of species distributions. In the north Pacific, during cooler Pleistocene glacial periods, regional extinction of northern populations caused by widespread glaciation may have divided trans-Pacific nearshore marine taxa into isolated eastern and western populations, potentially leading to trans-Pacific speciation. Nucella lima is a predatory marine gastropod living in the middle to low intertidal zone and is found on both sides of the Pacific. Although reported from Vancouver Island and northern Japan, sampling in the western Pacific shows a discontinuous distribution due to the species absence from much of the eastern Russian coast. Samples from both the eastern and western North Pacific were analyzed using the mtDNA marker cytochrome oxidase I (COI). Eastern and western populations are reciprocally monophyletic, with a net nucleotide divergence of 1.32%. Based on a conservative 1% rate of divergence we estimate an east/west split no earlier than the Pleistocene; given that gene lineage splits always predate population splits, this estimate is likely an upwardly biased estimate of population splitting time. Our data therefore supports the hypothesis that glacial-interglacial cycles of the Pleistocene caused geographic isolation leading to speciation in the north Pacific.