Risk of inbreeding: problem of mate choice and fitness effects?

Abstract

Mating with close kin may cause inbreeding depression with negative consequences to offspring and local populations. There exist mechanisms like kin-recognition or sex-specific dispersal to avoid mating with kin. In fluctuating population densities, like in many small mammals, both very low and very high densities provide conditions for inbreeding, if kin males are prone to stay in their natal area. Females are choosy and male dominance is thought to be the key feature when selecting mating partners. The aim of this study was to test the possible discrepancy in mate choice and negative fitness effects of inbreeding in two experiments, one in the laboratory and one in field enclosures. We asked (1) how the quality of the potential mating partners affects female choice regardless of relatedness and (2) how inbreeding affects the field populations created either from inbred or outbred individuals. Our results show that primiparous females in post-partum oestrus mated preferably with a dominant male, measured with their urine-marking behaviour, regardless if the selected male was brother or not. Only if the two males offered were of same dominance rank, the female mated with the non-kin male. However, the field experiment verified a negative effect of inbreeding in the bank vole. Thus, there seems to be a mismatch between female mate choice when selecting for dominance among resident males and population viability through long-term inbreeding depression. The study suggests the high importance of sex-biased dispersal as a mechanism to avoid kin individuals to meet in mate choice situations.