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Molecular taxonomy and phylogenetic analysis of the endangered blunt-nosed leopard lizard, Gambelia sila
The blunt-nosed leopard lizard (Gambelia sila) is a federally and state-listed endangered species, endemic to the San Joaquin Valley, Carrizo and Elkhorn Plains, and Cuyama Valley of central California. Habitat degradation has had a profound impact on the historic distribution and population size of G. sila. Although recognition of G. sila as a distinct species has been questioned by some authors (e.g., Cope 1900, Smith 1946), it is currently recognized as a full species separate from the wide-ranging long-nosed leopard lizard (G. wislizenii); however, genetic support for the specific status of G. sila is lacking. Furthermore, the genetic identity of leopard lizards in the purported hybrid zone between these two species in the Cuyama Valley in Santa Barbara and Ventura counties has not been evaluated using modern molecular techniques. Understanding the genetic identity of leopard lizards in the Cuyama Valley has practical as well as systematic implications. I investigated the sister taxon relationship of G. sila and G. wislizenii using 603 base pairs of sequence from the mitochondrial cytochrome oxidase III (CO3) gene from 37 individuals representing the two species sampled from various populations in western North America. Phylogenetic analysis revealed 17 haplotypes that are partitioned into two major clades that correspond to the range of G. sila and that of G. wislizenii haplotype groups, thus supporting the recognition of both lizards as distinct species. Additionally, I sequenced 682 base pairs of the mitochondrial cytochrome oxidase b (cyt b) gene from 34 individuals representing six populations of G. sila, including lizards from a remnant hybrid population. Phylogenetic analysis indicated that the cyt b sequences consisted of 18 haplotypes that are partitioned into three geographic clades: northern, central, and southern. All lizards from the Cuyama Valley exhibited the G. sila mitochondrial DNA signature and formed the "southern" clade that was joined as a sister group to the "central" clade. My morphological analysis placed some leopard lizards from the hybrid zone with true G. sila, whereas some aggregated with G. wislizenii, indicative of hybrid status. However, genetic signatures suggest that all lizards in the hybrid zone are true G. sila, and not hybrids.
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