Taxonomic affiliations and phylogeographic origins of melanoploid grasshoppers as revealed by molecular phylogenetic analyses

Members of one of the largest acridid subfamilies, Melanoplinae (Orthoptera: Acrididae), maintain a wide distribution throughout North America, South America, Europe and Asia. While the over 100 genera and 800 species are not particularly remarkable morphologically, they are notably diverse in male genitalic characters. Integral to taxonomic identification, such traits are believed to have played a significant role in the subfamily's evolution. The distributional and morphological features of the Melanoplinae render them ideal subjects for investigating the limits and applicability of molecular phylogenetic approaches to studies of phylogeography and the molecular-morphology conflict.; Findings described below are based on phylogenetic analyses of four mitochondrial genes.; The following scenario emerges with respect to origins, opposite to current beliefs. South America appears to be the place of origin for all melanoploids. Approximately 70 mya, North American taxa were established via dispersal from South America. In North America, evolution proceeded at a relatively rapid rate so that within 15 MY, the precursors of all extant Nearctic genera were established. Colonization of Eurasia had taken place by 50 mya. These intercontinental dispersal movements coincided with known geological and climatic events during these times.; Despite its prevalence in Europe and Asia, the tribe Podismini is North American in origin. Podismine dispersal into the Palearctic occurred about 50 mya, probably via the Bering Land Bridge. While Eurasian podismines are monophyletic, North American podismines are paraphyletic. Those occurring in eastern and western regions are each polyphyletic and were not founded by Eurasian ancestors traversing either the North Atlantic or Bering Land Bridges, as was once believed. These findings are easily reconcilable with the assumption of a North American origin for the podismines.; Within the species-rich Melanoplus, data indicate that the genus evolved rapidly during the last 4 MY. Among the many species relationships recovered in this study, the following are noteworthy: (1) Two relict species, M. madeleineae and M. gaspesiensis, are indeed related to M. borealis, especially the former. (2) Bohemanella is not a podismine but a melanopline and should be renamed. (3) The now-extinct Rocky Mountain Grasshopper, M. spretus, examined here for the first time using molecular characters, is a distinct species. M. spretus appears to have separated from its nearest relative, M. bruneri within the last million years. Separation of M. spretus from M. sanguinipes is more distant, a surprising result given the historical debate surrounding these two species.; Finally, this thesis argues that the morphological traits used for taxonomic purposes are probably subject to convergent evolution and are of dubious phylogenetic value.