Natural selection, gene flow, and population
structure in marine fishes

Grant Pogson, Ph.D.
University of California, Santa Cruz

Wednesday, February 21, 2001
3:00 p.m.—Pacific Forum

High levels of gene flow have been implicated in producing uniform patterns of genetic variation among populations of many marine fish species. However, molecular genetic studies on a growing number of marine fishes have revealed (1) small, but highly significant, genetic differentiation among natural populations, and (2) shallow phylogeographic structuring of both mitochondrial (mtDNA) and nuclear (nDNA) gene trees. Both observations are consistent with the hypothesis that the recent population history of marine fishes, rather than extensive gene flow per se, is responsible for their weak population structure.

I will present genetic data on populations of the Atlantic cod, Gadus morhua, from the northwestern Atlantic region that strongly suggest that recent population history is responsible for their minimal genetic differentiation. Our results suggest that interpreting limited genetic differences among populations of marine fishes (or other organisms) as reflecting high levels of ongoing gene flow should be made with caution.

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