Summary: Molecular Ecology (2005) 14, 3965­3976 doi: 10.1111/j.1365-294X.2005.02734.x
© 2005 Blackwell Publishing Ltd
Blackwell Publishing, Ltd.
Populationgeneticanalysisidentifiessource­sinkdynamics
for two sympatric garter snake species (Thamnophis elegans
and Thamnophis sirtalis)
MOLLIE K. MANIER and STEVAN J. ARNOLD
Department of Zoology, 3029 Cordley Hall, Oregon State University, Corvallis, OR 97331-2914, USA
Abstract
Population genetic structure can be shaped by multiple ecological and evolutionary factors,
but the genetic consequences of these factors for multiple species inhabiting the same envi-
ronment remain unexplored. We used microsatellite markers to examine the population
structures of two coexisting species of garter snake, Thamnophis elegans and Thamnophis
sirtalis, to determine if shared landscape and biology imposed similar population genetic
structures. These snakes inhabit a series of ponds, lakes and flooded meadows in northern
California and tend to converge on prey type wherever they coexist. Both garter snakes had
comparable effective population sizes and bidirectional migration rates (estimated using a
maximum-likelihood method based on the coalescent) with low but significant levels of
genetic differentiation (FST = 0.024 for T. elegans and 0.035 for T. sirtalis). Asymmetrical gene
flow revealed large source populations for both species as well as potential sinks, suggesting

Source: Arnold, Stevan J. - Department of Zoology, Oregon State University
Palumbi, Stephen - Hopkins Marine Station & Department of Biology, Stanford University
Pitnick, Scott - Department of Biology, Syracuse University

Collections: Biology and Medicine; Environmental Sciences and Ecology