ABSTRACT
Geographic variation in the gene frequencies corresponding to 15 polymorphic enzymes were studied in the common killifish Fundulus heteroclitus. Aat-A, Est-B, Fum-A, H6pdh-A, Mpi-A and Pgm-B showed clinal variation in allelic frequencies along the Atlantic coast of North America, while Aat-B, Ap-A, and the EST-C phenotypes did not. The clinal allelic variation of six previously examined loci (Ldh-B, Mdh-A, Gpi-B, Idh-A, Pgm-A, and 6-Pgdh-A) was extended to locations farther north. Gene diversity was lowest in the cold waters of northern latitudes and highest in the warmer waters of southern latitudes. The variety of clinal shapes and widths suggests that selection has affected the allelic distributions for at least some of these loci. This hypothesis is discussed with regard to the range contractions and extensions caused by the glacial advances and retreats during the Pleistocene.
