Social mating system affects the frequency of extra-pair paternity in house wrens

We tested two hypotheses regarding the effect of the social mating system on extra-pair paternity in an Illinois population of house wrens, Troglodytes aedonAccording to the genetic-quality hypothesis, polygynous males are of higher quality than monogamists, and monogamously paired females, in an attempt to obtain high-quality genes, should have a greater proportion of extra-pair nestlings in their nests than polygynously paired females. According to the trade-off hypothesis, polygynists, with temporally overlapping nests, will have a greater proportion of extra-pair nestlings in their nests than monogamists, because polygynists have difficulty guarding one or both of their social mates. DNA fingerprinting revealed that extra-pair paternity was most frequent in secondary nests of polygynists. The proportion of secondary broods with extra-pair nestlings increased with the temporal overlap of polygynists' nests, although this trend was not significant. Both results are consistent with the trade-off hypothesis but not with the genetic-quality hypothesis. We did not address the effects of genetic quality on male success at siring nestlings in the nests of other males. Although the trade-off hypothesis focuses on male mate guarding, female behaviours may also affect frequencies of extra-pair paternity. Secondary females may compensate for reduced male defence by engaging in extra-pair copulations with neighbours to reduce the likelihood that neighbours destroy their nests. Thus, in house wrens, female participation in extra-pair copulations in combination with male mate-guarding constraints may generate higher levels of extra-pair paternity in secondary broods than in primary polygynous or monogamous broods.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour