Monogamous male mice bias behaviour towards females according to very small differences in kinship

To the extent that relatedness between mates predicts their reproductive success, individuals are expected to bias their behaviours towards opposite-sex conspecifics according to differences in kinship. Here we show that monogamous male oldfield mice, Peromyscus polionotus rhoadsi, bias their social behaviour towards unfamiliar, distantly related females according to an average 1.3% difference in their kinship to these potential mates. Males in the present study favoured less-related females. Previous empirical investigations have not demonstrated behavioural biases based on such small kinship differences. Consequently, these small differences in kinship have been considered inadequate to drive the evolution of mate choice, particularly by males. Even a small incremental difference in mate quality, however, may significantly affect male reproductive success, especially for monogamous species or those that require maternal care. This study has demonstrated that the social preferences of male oldfield mice are distributed between females according to small differences in their kinship to these potential mates. (C) 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.