title: Females increase offspring heterozygosity and fitness through extra-pair matings.
abstract: Females in a variety of species commonly mate with multiple males, and there is evidence that they benefit by producing offspring of higher genetic quality; however, the nature of these genetic benefits is debated. Enhanced offspring survival or quality can result from intrinsic effects of paternal genes---'good genes'--or from interactions between the maternal and paternal genomes--'compatible genes'. Evidence for the latter process is accumulating: matings between relatives lead to decreased reproductive success, and the individual level of inbreeding--measured as average heterozygosity--is a strong fitness predictor. Females should thus benefit from mating with genetically dissimilar males. In many birds, social monogamy restricts mate choice, but females may circumvent this by pursuing extra-pair copulations. Here we show that female blue tits, Parus caeruleus, increase the heterozygosity of their progeny through extra-pair matings. Females thereby produce offspring of higher reproductive value, because less inbred individuals have increased survival chances, a more elaborate male secondary sexual trait (crown colour) and higher reproductive success. The cost of inbreeding may therefore be an important factor driving the evolution of female extra-pair mating.
authors.affiliation: Max Planck Research Centre for Ornithology, PO Box 1564, D-82305 Starnberg (Seewiesen), Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Foerster
authors.forename: Kaspar
authors.initials: K
authors.lastname: Delhey
authors.forename: Arild
authors.initials: A
authors.lastname: Johnsen
authors.forename: Jan T
authors.initials: JT
authors.lastname: Lifjeld
authors.forename: Bart
authors.initials: B
authors.lastname: Kempenaers
mesh_terms: D000818:Animals; D003116:Color; D003307:Copulation / Q000502:physiology*; D005260:Female; D006579:Heterozygote; D008098:Litter Size; D008297:Male; D012098:Reproduction / Q000502:physiology*; D012727:Sex Characteristics; D020308:Songbirds / Q000033:anatomy & histology / Q000235:genetics* / Q000502:physiology*; D015996:Survival Rate