Phylogeography of the plains killifish, Fundulus zebrinus

Drainage systems of the Great Plains and western Gulf Slope underwent subst antial changes through diversions and stream captures during the Pleistocen e, either as the result of the glacial advances or through independent geol ogic processes. The distributions of a variety of fishes that range across west-central North America, such as the plains killifish (Fundulus zebrinus ), are thought to be the product of this Pleistocene influence. We examined the geographic pattern of genetic variation in F. zebrinus using three all ozyme loci (n = 793), mitochondrial DNA restriction fragment length polymor phisms (RFLPs, n = 352), and sequencing of the mitochondrial cytochrome oxi dase I (COI, n = 23) in an attempt to understand the roles of dispersal and vicariance. The phylogeographic patterns were concordant between the alloz yme and mitochondrial data with the exception of the population in the Nort h Canadian River. The populations fell into three geographic assemblages, w hich we designated as northern, central, and southern. A large phylogenetic break (average Roger's D = 0.702; average sequence divergence in RFLPs = 4 .6%; average sequence divergence in COI = 5.5%) separated the northern/cent ral and southern assemblages. The northern region was likely colonized some time during the mid-Pleistocene. Fish in the Brazos and Pecos Rivers probab ly reached these drainages through stream captures of the Red River. The la rge phylogenetic break between the northern/central and southern clades sup ports previous attempts to recognize two species of plains killifish: F. ze brinus and F. kansae.