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1 July 2012 Genetic and Morphological Divergence Among Cooper's Hawk (Accipiter cooperii) Populations Breeding in North-Central and Western North America
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Abstract

Cooper's Hawk (Accipiter cooperii) populations breeding in the northern portion of the species' range exhibit variation in morphological traits that conforms to predictions based on differences in prey size, tree stand density, and migratory behavior. We examined genetic structure and gene flow and compared divergence at morphological traits (PST) and genetic markers (FST) to elucidate mechanisms (selection or genetic drift) that promote morphological diversification among Cooper's Hawk populations. Cooper's Hawks appear to conform to the genetic pattern of an east-west divide. Populations in British Columbia are genetically differentiated from north-central populations (Wisconsin, Minnesota, and North Dakota; pairwise microsatellite FST= 0.031-0.050; mitochondrial DNA ΦST = 0.177-0.204), which suggests that Cooper's Hawks were restricted to at least two Pleistocene glacial refugia. The strength of the Rocky Mountains—Great Plains area as a barrier to dispersal is further supported by restricted gene-flow rates between British Columbia and other sampled breeding populations. Divergence in morphological traits (PST) was also observed across study areas, but with British Columbia and North Dakota differentiated from Wisconsin and Minnesota, a pattern not predicted on the basis of FST and ΦST interpopulation estimates. Comparison of PSTand FSTestimates suggests that heterogeneous selection may be acting on Cooper's Hawks in the northern portion of their distribution, which is consistent with hypotheses that variation in prey mass and migratory behavior among populations may be influencing overall body size and wing chord. We were unable to distinguish between the effects of genetic drift and selection on tail length in the study populations.

©2012 by The American Ornithologists' Union. All rights reserved.
Sarah A. Sonsthagen, Robert N. Rosenfield, John Bielefeldt, Robert K. Murphy, Andrew C. Stewart, William E. Stout, Timothy G. Driscoll, Michael A. Bozek, Brian L. Sloss, and Sandra L. Talbot "Genetic and Morphological Divergence Among Cooper's Hawk (Accipiter cooperii) Populations Breeding in North-Central and Western North America," The Auk 129(3), (1 July 2012). https://doi.org/10.1525/auk.2012.11166
Received: 26 July 2011; Accepted: 1 March 2012; Published: 1 July 2012
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