Female house mice initially shun infected males, but do not avoid mating with them

Female house mice (Mus musculus) show preferences for the scent of healthy versus infected males, which may function to reduce risks of disease transmission or to obtain healthy, disease-resistant mates. It is not known whether such odor preferences result in differential male reproductive success (sexual selection), and therefore, we performed mate choice experiments with wild-derived mice. Females were allowed to fieely choose to mate between two males, one infected (Salmonella enterica) versus a sham control, and we conducted genetic paternity analyses on the offspring to assess male reproductive success. The males were restricted to their own cages to prevent male-male interactions and sexual coercion, and we performed the experiment in two different settings: in large-connected cages and in large enclosures. In the enclosures, we found that 86% of females were initially more attracted to the control males (initial social preference); however, our paternity analyses detected no difference in male reproductive success in either setting. Females often mated with both males (connected cages 32%, enclosures 44%), which shows that females frequently mate multiply—despite differences in male health—when they can choose their mates. These results raise caveats about mate choice studies that rely on proxy measures, such as odor preferences or time spent with potential mates. On the other hand, if females are less likely to locate infected than healthy males in the wild, then such a bias could still result in nonrandom mating. We suggest several additional issues that also need to be considered before ruling out parasite-mediated mate choice.