Mitochondrial DNA-Based Phylogeography of North American Rubber Boas, Charina bottae (Serpentes: Boidae)

We used 783 bp of mitochondrial DNA sequences to study the phylogeography of Charina bottae (rubber boa) in western North America, with an emphasis on populations from California (U.S.A.). Maximum-parsimony and maximum-likelihood methods identified a basal divergence within C. bottae that corresponds to southern and northern segments of its current distribution. These clades coincide with the ranges of the two recognized subspecies, C. b. umbratica in the south and C. b. bottae to the north. A subsequent cladogenetic event in the C. b. bottae clade resulted in two groupings, which we refer to as the Sierra Nevada and the Northwestern subclades, based on the geographic distribution of their constituent populations. The two subclades have completely allopatric distributions, with a genetic break in the vicinity of Lassen Volcanic National Park in northeastern California, an area that was subjected to glaciation during the Pleistocene and that has been volcanically active in the past 100 years. An earlier genetic study documented fixed differences between populations of bottae and umbratica in four of seven allozymes surveyed, and despite noticeable variation and overlap in the characters that define C. b. bottae and C. b. umbratica, the two forms still can be separated in most cases using a suite of morphological traits. All available evidence thus indicates that C. b. umbratica is a genetically cohesive, allopatric taxon that is morphologically diagnosable, and we conclude that it is an independent evolutionary unit that should be recognized as a distinct species, Charina umbratica.