Extrapair paternity and the opportunity for sexual selection in long-distant migratory passerines

Extrapair fertilizations (EPFs) are frequently documented in songbirds; however, the extent to which this reproductive tactic contributes to variance in male reproductive success and hence the strength of sexual selection on males remains little studied. Using 2 approaches, intraspecific and comparative, we test the hypothesis that the contribution of EPFs to variance in male fitness increases with migration distance in north temperate songbirds. Using data on the genetic mating system of the scarlet rosefinch Carpodacus erythrinus, a long-distance migrant, we show that the number of extrapair mates and within-pair paternity are the most important components of variance in male reproductive success. There was no evidence of a trade-off between extrapair and within-pair success of individual males as males successful in procuring EPFs were less likely to be cuckolded. Comparative data reveal that the opportunity for sexual selection due to EPFs is positively associated with both migration distance and breeding synchrony in north temperate passerines, and we discuss several mechanisms that could extend these relationships. In general, these data suggest that EPFs have a potential to play an important role in the evolution of sexually selected traits in long-distance migratory songbirds such as rosefinches.