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1 August 2009 Subtle Edge-of-Range Genetic Structuring in Transcontinentally Distributed North American Tree Swallows
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Understanding how genetic variation in the Tree Swallow (Tachycineta bicolor) is geographically structured is informative because this broadly distributed North American bird is increasingly used as a model for studies of mating systems, life-history traits, and physiology. We explored patterns of phylogeographic differentiation across the Tree Swallow's breeding range by using nine microsatellite loci and a mitochondrial DNA sequence marker. Contrary to this species' high population-level variation in life-history traits and other ecologically important characteristics, we found no genetic structuring across the majority of its distribution, spanning Tennessee, New York, and Alaska, but we found that birds from California form a distinct yet subtly differentiated genetic cluster. The Tree Swallow can be characterized as a species with both continent-wide genetic panmixia and slight differentiation at one edge of its breeding distribution. This pattern of genetic variation has implications for understanding the underlying basis of geographic variation in this species' life history and other phenotypic traits.

© 2009 by The Cooper Ornithological Society. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website,
Laura M. Stenzler, Christopher A. Makarewich, Aurélie Coulon, Daniel R. Ardia, Irby J. Lovette, and David W. Winkler "Subtle Edge-of-Range Genetic Structuring in Transcontinentally Distributed North American Tree Swallows," The Condor 111(3), 470-478, (1 August 2009).
Received: 6 October 2008; Accepted: 1 April 2009; Published: 1 August 2009

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