Range-wide population structure and history of the northern quahog (Merceneria merceneria) inferred from mitochondrial DNA sequence data.

Baker, P., Austin, J. D., Bowen, B. W., and Baker, S. M. 2008. Range-wide population structure and history of the northern quahog (Merceneria merceneria) inferred from mitochondrial DNA sequence data. – ICES Journal of Marine Science, 65: 155–163.The northern quahog (Mercenaria mercenaria) is a commercially important bivalve distributed in the NW Atlantic from Florida to Nova Scotia. We report on population genetic analyses, based on 528 bp of mitochondrial COI gene, for 10 locations across the range of M. mercenaria (n = 297). Our analyses revealed no evidence of cryptic evolutionary lineages, but modest population structure (ϕST = 0.0213; p = 0.0019) with a significant partition at Cape Hatteras and a weakly supported partition at Cape Cod. Samples from the west coast of Florida (Gulf of Mexico) were not significantly different from most Atlantic populations, despite a 600 km gap in distribution along South Florida, and a well-documented biogeographic break at Cape Canaveral. These findings support the thesis that the Gulf of Mexico population is the product of a recent introduction. Samples north of Hatteras decrease in diversity with increasing latitude, probably indicating post-glacial range extension, a conclusion supported by a highly significant Fu's F-statistic (−99.14; p < 0.001) indicating population expansion. Mercenaria mercenaria stocks in the Atlantic include a single evolutionary unit divided into at least three closely related populations, though this does not preclude regional adaptive differences between northern, central, and southern populations. [ABSTRACT FROM PUBLISHER]