Microsatellite identification of extrapair sires in a socially monogamous warbler

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Abstract
Few studies of avian mating systems have identified the sires of extrapair young, and hence it has been difficult to determine the scale at which reproductive interactions occur. For instance, females may be free to copulate with any male in the population (a “global” scale of interactions), or females may be restricted to copulating only with males on neighboring territories (a “local” scale). The scale of such interactions has important consequences for an understanding of the evolutionary causes and consequences of extrapair fertilizations. We used five hypervariable microsatellite loci and multilocus DNA fingerprinting to examine parentage of more than 400 nestling black-throated blue warblers (Dendroica caerulescens). Extrapair fertilizations were common, and the microsatellite markers allowed us to identify the sires for 89% of the young analyzed. Most identified extrapair sires were males on neighboring or nearby territories, and most nestlings for whom we could not identify a sire came from territories at the edge of the study plot. Thus, reproductive interactions appear to be more local than global in this population. Extrapair fertilizations contributed significantly to total variation in male reproductive success. However, the standardized variance in male reproductive success (0.68-0.74) was not substantially greater than that for females (0.53-0.60), and the contribution of extrapair fertilizations (9-14%) was much lower than the contribution of within-pair fertilizations (75-77%). This suggests that the local scale of reproductive interactions may limit variation in male reproductive success and hence the opportunity for selection.

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