DNA Analysis
While the findings of the ICZN have given the San Francisco garter snake unique taxonomic standing for now, a molecular study challenges the subspecific status of this population. Janzen analyzed sequences in mitochondrial DNA to determine relationships within the common garter snake (T. sirtalis). Janzen found that molecular evidence differed, often sharply, with the territorial boundaries of subspecies named on phenotypic variation. He further deduced that local environmental forces were more significant in shaping the color patterns shown by the garter snakes than shared common ancestry, and concluded all morphologically based subspecies in the western U.S. to be subject to revision. This result strongly suggests that the color traits that are diagnostic for (T.s. tetrataenia) are the result of local selection rather than long-term isolation from other races of (T. sirtalis) in central California. On the other hand, the article places the three nearest populations of T. s. infernalis to T.s. tetrataenia in Sonoma County, Contra Costa County, and Santa Clara County into a separate group that exhibits an "elevated rate of molecular evolution". The authors suggest that sequencing nuclear DNA may provide a more precise analytical tool to crack some of the ultimate taxonomic quandaries of the San Francisco garter snake and its relatives.
Read more about this topic: San Francisco Garter Snake
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