Assessing the prevalence of common patterns and unique events in the formation of biotas: a study of fish taxa of the North American central highlands

Abstract

The Central Highlands fish fauna is a complex assemblage of hundreds of species, many showing a high degree of endemicity. This diversity has traditionally been explained by invoking relatively simple vicariance and dispersal scenarios. In my study, I assembled all existing phylogenies of fishes from the Central Highlands to conduct a Phylogenetic Analysis for the Comparison of Trees, which revealed that vicariance and dispersal events have both played a role in the formation of the Central Highlands ichthyofaunas. Evidence of co-ordinated dispersal and area reticulation was also discovered. The fauna of some regions, in particular the Tennessee River basin, is shown to have accumulated due to multiple vicariance and dispersal events. One mitochondrial and seven nuclear loci were sequenced for the members of the Etheostoma zonale species group. A high degree of geographical structure was found, with twelve reciprocally monophyletic mitochondrial clades in E. zonale, and nine in E. lynceum. Species tree analysis demonstrated the monophyly of both species. One clade found in the Upper Tennessee River basin was found to have undergone introgression with a second clade. One mitochondrial and three nuclear loci were sequenced for the members of the Luxilus zonatus species group. Four mitochondrial introgression events were found in the group, involving all three members of the L. zonatus group as well as two other species of Luxilus. The geographical extent of the introgression events varies, as does their time of occurrence. A Hierarchical Approximate Bayesian Computation was performed on a set of sister clades of three taxa found in the Ozark and Ouachita Mountains: two clades of Etheostoma zonale, two clades of E. blennioides, and Luxilus cardinalis and L. pilsbryi. All taxon pairs share the same geographical split; the analysis showed that two of these divergences did not happen at the same time as the third, and are thus pseudocongruent. The results of this study show that the Central Highlands ichthyofauna has a more complex history than has been believed, and suggest methods of reconstructing such complex histories which should prove useful in biogeographical studies of similarly complex systems.