Gene Flow and Local Adaptation in a Colonially Nesting Dimorphic Bird: The Lesser Snow Goose (Anser caerulescens caerulescens)

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Abstract
The interplay between gene flow and selection is examined in the dichromatic lesser snow goose (A. c. caerulescens). A major component of this species nests in several large colonies (segments) in the Canadian arctic and migrates to the gulf coast of Texas and Louisiana [USA], where there is considerable mixing of birds from different segments. Pair formation occurs when birds from different nesting segments are mixing and frequently occurs between birds from different segments. Females usually return to their natal nesting segment, whereas males only do so if they pair with birds from their own natal segment. The consequence is considerable gene flow among the different nesting segments. Gene flow into the small nesting segment at La Perouse Bay, Manitoba, is estimated to be around 50%/generation. Gene flow into the larger segments is expected to be somewhat less. With this amount of gene flow, one would expect little local adaptation within the various nesting segments. This conclusion is examined in view of the apparently stable differences in color frequencies among the nesting segments. Behavioral aspects of the breeding biology of the species, rather than natural selection, sufficiently account for both the massive gene flow and the color differentiation among nesting segments.

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