Interest of mice in conspecific male odours is influenced by degree of kinship

Abstract

SMELL affects many aspects of the social and sexual behaviour of rodents^1,2. For example, fighting in pairs of male mice is increased if one of the participants is made to smell unfamiliar by rubbing it with the urine of a strange male³. It has also been suggested that olfactory cues play an important part in mate choice⁴. In both rats⁵ and mice⁶, females which have been reared by artificially scented mothers have, when adult, been found to prefer males treated with this same scent to normal individuals. By contrast, Mainardi⁷ has found that female mice, reared in the presence of their fathers, later preferred to mate with males of a different strain. The difference between these two results may stem from the degree of strangeness involved, females preferring males which smell slightly unfamiliar rather than very familiar or totally strange. The results of the experiments using artificial odours suggest that early learning provides the yardstick by which unfamiliarity is judged^5,6. Such a system may have an important role in assortative mating, enabling females given a choice to mate with those males by whom they are likely to conceive the best-adapted offspring. On this hypothesis females might be expected to prefer a small degree of unfamiliarity as an adaptation which minimises the chance of inbreeding. They might also be expected to reject males which smell very strange. At an extreme, this would avoid interspecific hybridisation, but it may also be disadvantageous within a species for very dissimilar individuals to mate as this would be likely to lead to the break-up of co-adapted gene complexes and thus the production of offspring of lower fitness^8,9. We report here our examination of these predictions. Our data suggest that the olfactory preferences of female mice are consistent with this hypothesis.