Causes and consequences of male and female partner preference in the monogamous oldfield mouse (Peromyscus polionotus subgriseus)

This thesis investigates the causes and consequences of male and female partner preference and pair bond formation in the monogamous, bi-parental oldfield mice (Peromyscus polionotus subgriseus). Due to the fact that monogamy and long-term pair bonds are rare in mammals, few studies have explored the existence of male and female preference in the same species or have attempted to measure the fitness benefits to being choosy.; The expression of partner preference and the formation of long-term pair bonds are critical for the reproductive success of monogamous, biparental species. In this thesis, I demonstrated that males and females expressed partner preferences and that they based their preferences on different traits and at different times in their lives: Males chose the less related females in partner preference tests, thereby minimizing the inbreeding of their offspring. Male interest in his partner determined whether the female conceived or not. Males that initiated more interactions than they terminated and that spent a large amount of time engaged in affiliative behaviors towards their partners had partners that conceived a litter. In this initial phase of cohabitation, females may very well be assessing the quality of their potential partners. Furthermore, prior reproductive success determined subsequent female preference. Reproductively successful females were significantly more likely to choose their partner than the unfamiliar male in a subsequent partner preference test.; In order to understand the proximate mechanisms regulating the variability in reproductive success within and between individuals, I validated a corticosterone RIA assay for fecal samples in order to measure the changes in plasma corticosterone (CORT) and fecal corticosteroid concentrations in male and female mice over the course of the female's reproductive cycle. The pattern of female corticosteroid concentrations mirrored the well-established pattern of plasma CORT during the pregnancy. Males that successfully raised their litters had low corticosteroid concentrations throughout their partner's pregnancy. Unsuccessful males, however, had significantly higher fecal corticosteroid concentrations at term than males that raised their pups to weaning. This suggests that males were responsible for the loss of the litter and that pre-partum corticosteroid concentrations can be used to predict paternal behavior.