1. ¹Sutton Avian Research Center, University of Oklahoma, Bartlesville, OK, USA
2. ²University of Alaska Museum, Fairbanks, AK, USA
3. ³Department of Forest Sciences, Centre for Applied Conservation Research, University of British Columbia, Vancouver, British Columbia, Canada
4. ⁴Department of Biological Sciences, Stanford University, Stanford, CA, USA
5. ⁵Oklahoma Biological Survey and Department of Zoology, University of Oklahoma, Norman, OK, USA
6. ⁶Zoologisches Museum, Universität Zürich, Zürich, Switzerland

Correspondence: Dr CL Pruett, Sutton Avian Research Center, University of Oklahoma, PO Box 2007, Bartlesville, OK, 74005-2007, USA. E-mail: cpruett@ou.edu

Received 5 September 2007; Revised 4 March 2008; Accepted 26 March 2008; Published online 7 May 2008.

Abstract

Historic events and contemporary processes work in concert to create and maintain geographically partitioned variation and are instrumental in the generation of biodiversity. We sought to gain a better understanding of how contemporary processes such as movement and isolation influence the genetic structure of widely distributed vagile species such as birds. Song sparrows (Melospiza melodia) in western North America provide a natural system for examining the genetics of populations that have different patterns of geographic isolation and migratory behavior. We examined the population genetics of 576 song sparrows from 23 populations using seven microsatellite loci to assess genetic differentiation among populations and to estimate the effects of drift and immigration (gene flow) on each population. Sedentary, isolated populations were characterized by low levels of immigration and high levels of genetic drift, whereas those populations less isolated displayed signals of high gene flow and little differentiation from other populations. Contemporary dispersal rates from migratory populations, estimated by assignment test, were higher and occurred over larger distances than dispersal from sedentary populations but were also probably too low to counter the effects of drift in most populations. We suggest that geographic isolation and limited gene flow facilitated by migratory behavior are responsible for maintaining observed levels of differentiation among Pacific coastal song sparrow populations.