Extrapair paternity in the great tit (Parus major): a test of the "good genes" hypothesis

In 1993 and 1994 we determined the frequency of extrapair paternity in broods of great tits, Parus major, using multilocus DNA fingerprinting. We found no instances of intraspecific brood parasitism, but 40% of broods (31/78) contained extrapair-fathered young and 8.5% of offspring (55/681) were extrapair. We identified the genetic fathers of 60% of the extrapair nestlings (35/58). Males with full and lost paternity did not differ significantly in baits that have been suggested to indicate male quality, nor did the genetic and social fathers of extrapair offspring. In 1993, cuckolded males sired more offspring that recruited to the subsequent bleeding season than males with full paternity. Moreover, even though genetic fathers of extrapair young (EPY) sired more fledglings than the males they cuckolded, genetic and social fathers of EPY did not differ in the number of recruits sired. Also, the EPY of a brood did not survive better than their half sibs. Thus, our results do not support the hypothesis that females choose better quality males fur extrapair matings ("good genes" hypothesis). Further, the level of extrapair paternity differed markedly between the two years. Our data show that females are constrained in their extrapair activities by the availability of extrapair mates. This is at least partly due to yearly differences in breeding synchrony.