Vicariance Biogeography, Parsimony, and Evolution in North American Freshwater Fishes

Abstract

The North American freshwater fish fauna exhibits considerable species diversity and patterns of endemism. The fauna has enormous potential for use in investigations and tests of biogeographic and evolutionary theories. Many of these studies are presently impossible to execute, however, because of our impoverished knowledge of native fish species relationships. Fish communities of the Central Highland Regions of eastern North America are exceptions to this observation. The fauna is diverse and contains patterns of endemism identifiable as gen- eralized biogeographic tracts. This ichthyofauna is reviewed and employed as a case study in applications of phylogenetic relationships of organisms in vicariance biogeography. In this new method species relationships and distributions are coded in a binary and multistate data matrix and analyzed using a parsimony algorithm to elucidate the age, origin, and biogeographic history of the fauna. Rivers inhabited by species are analogous to taxa; relationships between species and their distributions are analogous to characters possessed by each of the taxa (Rivers). From seven fish clades, 33 equally parsimonious cladograms are obtained for the Central Highland drainages. The resulting strict consensus cladogram is consistent with the known pre- Pleistocene geological history of eastern North American rivers and supports the hypothesis of an ancient ichthyofauna. With this group of fish clades the Mobile Basin forms the sister group to all rivers of the Mississippi River Basin. Among the Mississippi River tributaries, a clade inclusive of the Tennessee, Duck, Cumberland, and Green rivers forms the sister group with the Salt River in Kentucky. This clade is sister to a large Teays-Mississippi clade. Within the latter group, a sister-group relationship is obtained between tributaries of the upper Ohio River, formerly of the Teays River, and a clade inclusive of rivers across the glaciated Central Lowlands and into the Interior Highlands. These relationships may be predicted from pre-glacial drainage patterns, but not by present-day drainage connections. Concordance between the known pre- glacial drainage history and the drainage cladogram supports the existence of a diverse and widespread pre-Pleistocene Central Highlands ichthyofauna. (Biogeography; freshwater fishes; parsimony; phylogenetic systematics; evolution; speciation; extinction.)