Phylogeography of the pitviper clade Agkistrodon: historical ecology, species status, and conservation of cantils

We used mitochondrial DNA sequences from three gene regions and two tRNAs ( ND4, tRNA-HIS-SER, 12S, and 16S rDNA) to investigate the historical ecology of the New World pitviper clade Agkistrodon, with emphasis on the disjunct subspecies of the cantil, A. bilineatus. We found strong evidence that the copperhead (A. contortrix) is basal to its congeners, and that the cottonm outh (A. piscivorus) is basal to cantils. Phylogeography and natural histor y of the living terminal taxa imply that Agkistrodon primitively occupied r elatively temperate habitats, with subsequent evolution of tropicality in a ncestral A. bilineatus. Our best supported phylogeny rejects three gulf arc scenarios for the biogeography of A. bilineatus. We find significant stati stical support for an initial divergence between populations on the east an d west coasts of Mexico and subsequent occupancy of the Yucatan Peninsula, by way of subhumid corridors in northern Central America. Based on phylogen etic relationships, morphological and molecular divergence, and allopatry w e elevate A. b. taylori of northeastern Mexico to species status. Taylor's cantil is likely threatened by habitat destruction and small geographical r ange, and we offer recommendations for its conservation and management.