POPULATION GENETIC-STRUCTURE IN THE BLACK RAT SNAKE - IMPLICATIONS FOR MANAGEMENT

Assessments of population genetic structure and diversity can be of va lue in formulating management plans for threatened species. Using rand omly amplified polymorphic DNA markers, we found evidence of significa nt genetic structure among black rat snakes (Elaphe obsoleta) sampled at three spatial scales. highly isolated (1500-1900 km apart) populati ons were strongly divergent (F-ST = 0.242-0.323), whereas populations more proximal (less than or equal to 465 km apart) although currently isolated, exhibited far less divergence (F-ST = 0.019). A considerable proportion (80%) of total genetic diversity was due to differences am ong individuals within populations, although differences among populat ions (8%) also wee significant. At the scale of sub-populations (local populations 15-50 km apart), differentiation was generally moderate ( F-ST = 0.058). Our estimates of Nei's genetic distance for sub-populat ions (0.014) approximated (mean = 0.044) those obtained in other studi es that have assessed differentiation between snake populations based on variation in allozymes. The majority (ca. 86%) of total genetic var iance across five sub-populations was attributable to differences amon g individuals, although differences among sub-populations (ca. 13%) al so were significant. We found little evidence of genetic structure (F- ST = 0.006) between pairs of hibernacula, our finest spatial scale (sa mples 1-2 km apart), if they were located in natural habitats. In cont rast, a pair of hibernacula sampled in an urban area exhibited genetic structure equivalent to some sub-population differences (F-ST = 0.039 ), suggesting interrupted gene flow related to urban development. Our results have direct implications for ranking populations in terms of t heir conservation value and the genetic management of threatened snake s.