To know him is to love him? Familiarity and female preference in the harvest mouse, Micromys minutus

Mate choice in mammals is often influenced by the presence or absence of familiarity with the potential mates. While females of many social species prefer to mate with unfamiliar males, many solitary female rodents exhibit a preference for familiar males. The harvest mouse is such a solitary species, with no intersexual size dimorphism, and in which the females are possibly dominant to the males. This leaves the females’ choice of mate relatively unhindered by direct male coercion or male–male competition. To isolate the role of familiarity in female preference in the harvest mouse, we conducted a two-stage controlled choice experiment, in which the female had a choice between the scent of two males, one familiar and one unfamiliar to her, and, in the second stage, two tethered males. When only olfactory cues were available to the females, no preferences were observed. The results of the live test, however, showed that female harvest mice preferred familiar males over unfamiliar ones when they were in oestrus. Furthermore, females spent more time in proximity to unfamiliar males when they were not in oestrus; and the difference in the weights of the males affected the strength of the female’s response, which was opposite for oestrous and dioestrous females. These results support the hypothesis that female harvest mice prefer mating with a familiar male, point to an interaction between familiarity and male size in female preference and highlight the importance of the female’s reproductive state during mate preference tests.