An experimental test of relatedness-based mate discrimination in a social lizard

One of the major decisions individuals of many species make when deciding who to mate with is whether or not to inbreed. The prevailing theory is that individuals should avoid mating with closely related individuals because of the fitness costs associated with decreased offspring quality. However, theoretical work has suggested that levels of inbreeding depression need to be considerable for these costs to outweigh the possible, kin selected, benefits of inbreeding. While evidence for a preference for inbreeding exists in the literature, empirical results currently lag well behind theory. Here, we conducted an experiment to examine mate discrimination and preference with respect to relatedness in a natural population of the family living lizard, Liopholis whitii. We show that both male and female L. whitii distinguish between related and unrelated individuals and, furthermore, that both sexes preferentially associate with more closely related members of the opposite sex. These results correspond closely with patterns of pairing observed in the wild where both males and females have been shown to choose mating pairs that are more closely related to them than expected by chance. Combined, our findings suggest that mate choice in this system may represent an active preference for mating with related individuals rather than a result of passive constraints associated with population viscosity.