Friday, October 29, 2010

Snakes and Roads

Like many herpetologists, I have spent a considerable amount of time driving roads in search of snakes. Roads can be particularly productive for finding snakes. Since many species are cryptic in their natural habitats - making them difficult to see, most species stand out on roads. Nocturnal species are also relatively easy to see when they are crossing a road because of their reflection in the headlights. Roads have undoubtedly played an important role in the discovery of new knowledge of snakes. But roads are also detrimental to snakes. The Prairie Kingsnake (Lampropeltis calligater) and the Eastern Fox Snake (Pantherophis gloydi) have shown aversions to crossing roads. Roads fragment the habitat, they create edge habitats as the cut through forests, grasslands, and deserts and they may act as barriers for some species. Now, Clark et al. (2010) have demonstrated that even small, recently constructed roads may have a significant impact on the population's genetic structure of some snakes but not others. The authors combined fine-scale molecular genetics with behavioral and ecological data to investigate the impacts of roads on population structure and connectivity. Microsatellite markers were used to characterize genetic variation within and between populations of Timber Rattlesnakes (Crotalus horridus) using dens in regions fragmented by roads. They discovered snake populations that used dens  isolated by roads had  lower genetic diversity and higher genetic differentiation than snakes in hibernacula in contiguous habitat. Snake populations disrupted by roads have fewer matings between populations, than those populations not crossed by roads.  It turns out, roads are extremely effective barriers to gene flow, given how recently they were constructed. Species with a long generation time (10 years), like Timber Rattlesnakes, have been exposed to roads as barriers for a relatively few generations - 7 to 10 generations for the populations studied, and yet their effects can be detected.

R. W. Clark, W. S. Brown, R. Stechert, K. R. Zamudio. 2010. Roads, Interrupted Dispersal, and Genetic Diversity in Timber Rattlesnakes. Conservation Biology, 24:1059–1069.

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