The role of genetic constraints and social environment in explaining female extra-pair mating

Why females of socially monogamous species copulate with males other than their partner has been a long-standing, unresolved puzzle. We previously reported that female promiscuity appears to be a genetic corollary of male promiscuity (intersexual pleiotropy hypothesis). Here we put this earlier finding to a critical test using the same population of zebra finches Taeniopygia guttata. After three generations of artificial selection on male courtship rate, a correlate of extra-pair mating, we assess whether female promiscuity changed by indirect selection and we re-examine the crucial genetic correlations. Our new analyses with substantially increased statistical power clearly reject the hypothesis that male and female promiscuity are genetically homologous traits. Our study highlights that individual females show low repeatability in extra-pair mating behavior across different social environments. This emphasizes the potential importance of pair bond strength and the availability of favored extra-pair males as factors explaining variation in patterns of female promiscuity.