Abstract
BackgroundIt is often proposed that females should select genetically dissimilar mates to maximize offspring genetic diversity and avoid inbreeding. Several recent studies have provided mixed evidence, however, and in some instances females seem to prefer genetically similar males. A preference for genetically similar mates can be adaptive if outbreeding depression is more harmful than inbreeding depression or if females gain inclusive fitness benefits by mating with close kin. Here, we investigated genetic compatibility and mating patterns in an insular population of house sparrow (Passer domesticus), over a three-year period, using 12 microsatellite markers and one major histocompability complex (MHC) class I gene. Given the small population size and the distance from the mainland, we expected a reduced gene flow in this insular population and we predicted that females would show mating preferences for genetically dissimilar mates.ResultsContrary to our expectation, we found that offspring were less genetically diverse (multi-locus heterozygosity) than expected under a random mating, suggesting that females tended to mate with genetically similar males. We found high levels of extra-pair paternity, and offspring sired by extra-pair males had a better fledging success than those sired by the social male. Again, unexpectedly, females tended to be more closely related to extra-pair mates than to their social mates. Our results did not depend on the type of genetic marker used, since microsatellites and MHC genes provided similar results, and we found only little evidence for MHC-dependent mating patterns.ConclusionsThese results are in agreement with the idea that mating with genetically similar mates can either avoid the disruption of co-adapted genes or confer a benefit in terms of kin selection.
Highlights
It is often proposed that females should select genetically dissimilar mates to maximize offspring genetic diversity and avoid inbreeding
According to the inbreeding avoidance hypothesis, for example, females mated with closely related males should engage in extra-pair copulations with genetically dissimilar mates [3], whereas the outbreeding avoidance and the kin selection hypotheses predict that females should engage in extra-pair copulations with genetically similar males [8,33]
We studied mate choice both for social and extra-pair mates in a small insular population of the house sparrow (Passer domesticus), using microsatellite loci and major histocompability complex (MHC)
Summary
It is often proposed that females should select genetically dissimilar mates to maximize offspring genetic diversity and avoid inbreeding. Extra-pair mating presents an opportunity to examine the processes governing mate choice in the absence of any potential direct benefit since the extrapair male does not contribute to parental care. According to the inbreeding avoidance hypothesis, for example, females mated with closely related males should engage in extra-pair copulations with genetically dissimilar mates [3], whereas the outbreeding avoidance and the kin selection hypotheses predict that females should engage in extra-pair copulations with genetically similar males [8,33]. Molecular tools have helped to test the hypothesis that genetic benefits from mate choice include increasing offspring heterozygosity at the major histocompatibility complex (MHC) loci [34,35,36,37,38,39]. It has been suggested that ‘if there is an optimal level of MHC heterozygosity for combating infections, females should prefer to mate with males that have intermediate levels of MHC dissimilarity’ [35], and subsequent work has provide evidence that female preferences depend on males’ individual allelic diversity [39,42,43]
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