MOLECULAR SYSTEMATICS OF THE CANIDAE

Despite numerous systematic studies, the relationships among many spec ies within the dog family, Canidae, remain unresolved. Two problems of broad evolutionary significance are the origins of the taxonomically rich canid fauna of South America and the development in three species of the trenchant heel a unique meat-cutting blade on the lower first molar. The first problem is of interest because the fossil record prov ides little evidence for the origins of divergent South American speci es such as the maned wolf and the bush dog. The second issue is proble matic because the trenchant heel, although complex in form, may have e volved independently to assist in the processing of meat. We attempted to resolve these two issues and five other specific taxonomic controv ersies by phylogenetic analysis of 2,001 base pairs of mitochondrial D NA (mtDNA) sequence data from 23 canid species. The mtDNA tree topolog y, coupled with data from the fossil record, and estimates of rates of DNA sequence divergence suggest at least three and possibly four Nort h American invasions of South America. This result implies that an imp ortant chapter in the evolution of modem canids remains to be discover ed in the fossil record and that the South American canid endemism is as much the result of extinction outside of South America as it is due to speciation within South America. The origin of the trenchant heel is not well resolved by our data, although the maximum parsimony tree is weakly consistent with a single origin followed by multiple losses of the character in several extant species. A combined analysis of the mtDNA data and published morphological data provides unexpected suppo rt for a monophyletic South American canid clade. However, the homogen eity partition tests indicate significant heterogeneity between the tw o data sets.