MITOCHONDRIAL-DNA SEQUENCE VARIATION AND GENETIC DIFFERENTIATION AMONG COLUBRINE SNAKES (REPTILIA, COLUBRIDAE, COLUBRINAE)

Nucleotide sequence variation in a portion of the mitochondrial 16S ri bosomal RNA gene was assessed to investigate systematic affinities wit hin the snake subfamily Colubrinae. A total of 391 base pairs from eac h of 33 taxa were aligned, with Thamnophis as the outgroup to the Colu brinae. Data were analyzed using both distance (145 sites) and parsimo ny (75 sites) algorithms. Analyses were concordant in showing that alt hough morphologically resembling a ratsnake, the Asian Gonyosoma oxyce phalum is genetically more similar to the North American racer lineage that includes Coluber constrictor and Masticophis flagellum than to a ny ratsnake examined. All other ratsnakes sampled comprise a monophyle tic group separate from the remaining colubrines. Within this ratsnake clade, the Nearctic ratsnakes can be distinguished as a monophyletic group. At least nine separate racer lineages can be identified. With t hree exceptions, racers from the same geographical region are genetica lly more similar to one another than to colubrines of other geographic origin. Finer resolution of phylogenetic affinities among taxa within this subfamily will require additional sequence data and more extensi ve sampling of taxa. The relative degree of sequence divergence observ ed between the tribes (racers and ratsnakes) sampled is consistent wit h other biochemical estimates of protein divergence, as well as with f ossil evidence, that suggests a Miocene divergence between the ratsnak es and other colubrine lineages.