PARSIMONY, MOLECULAR EVOLUTION, AND BIOGEOGRAPHY - THE CASE OF THE NORTH-AMERICAN GIANT SALAMANDER

To draw biogeographic conclusions about the Central Highlands region o f the United States, we reconstructed the phylogeny of hellbender (Cry ptobranchus alleganiensis) populations from restriction-site Variation in mtDNA. We were unable to root the phylogeny using an outgroup and therefore could not weight restriction-site gains more heavily than si te losses. As a result, maximum parsimony results in low phylogenetic resolution because of high levels of homoplasy in the data set. Use of a recently published algorithm based on an explicit model of molecula r evolution yielded much greater resolution of the mtDNA relationships . This phylogeny indicates the two subspecies of hellbenders are parap hyletic with respect to one another. Hellbenders found in the southern Ozarks (C. a. bishopi) are either most closely related to populations of C. a. alleganiensis inhabiting the Tennessee River drainage or are so divergent that phylogenetic affinities are undetectable. Extremely low levels of divergence among mtDNA haplotypes found in populations from Pennsylvania, Indiana, Illinois, and the northern Missouri Ozarks suggest a recent, probably post-Pleistocene, invasion of this region from a refugium in one of these areas. Biogeographic hypotheses of the causes and timing of hellbender distributions differ significantly fr om those postulated from analyses of fish species relationships. Possi ble reasons for the discrepancy are discussed.