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Item Sexual selection drives the coevolution of male and female reproductive traits in Peromyscus mice(Wiley, 2022-12-08) Weber, William David; Fisher, Heidi S.When females mate with multiple partners within a single reproductive cycle, sperm from rival males may compete for fertilization of a limited number of ova, and females may bias the fertilization of their ova by particular sperm. Over evolutionary timescales, these two forms of selection shape both male and female reproductive physiology when females mate multiply, yet in monogamous systems, post-copulatory sexual selection is weak or absent. Here, we examine how divergent mating strategies within a genus of closely related mice, Peromyscus, have shaped the evolution of reproductive traits. We show that in promiscuous species, males exhibit traits associated with increased sperm production and sperm swimming performance, and females exhibit traits that are predicted to limit sperm access to their ova including increased oviduct length and a larger cumulus cell mass surrounding the ova, compared to monogamous species. Importantly, we found that across species, oviduct length and cumulus cell density are significantly correlated with sperm velocity, but not sperm count or relative testes size, suggesting that these female traits may have coevolved with increased sperm quality rather than quantity. Taken together, our results highlight how male and female traits evolve in concert and respond to changes in the level of post-copulatory sexual selection.Item DIVERGENT MATING STRATEGIES ACROSS THE PEROMYSCUS GENUS DRIVE REPRODUCTIVE TRAIT DIVERSITY(2022) Weber, William David; Fisher, Heidi S; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The study of sexual selection and reproductive biology are dynamic research fields that contribute to basic research, public health, agriculture, and conservation. Peromyscus mice are an important model for studying the evolution of reproductive traits shaped by sexual selection due to the natural diversity of mating systems in this genus. Like most rodents, the ancestral mating strategy of Peromyscus is believed to be promiscuity, but monogamy has evolved independently at least twice. In this dissertation, I investigate how the divergent mating systems in Peromyscus have shaped the diversity of reproductive traits using six species (three monogamous and three promiscuous). First, I characterize the estrous cycle and show that promiscuous species display more intense estrous signaling than monogamous species, but I find a uniform cycle length across the genus. Moreover, I report a method to hormonally-induce ovulation in two species, P. polionotus (monogamous) and P. maniculatus (promiscuous). Second, to investigate the co-evolution of male and female reproductive traits, I examined six species that have evolved under divergent sexual selection pressures and found a correlated expression of traits associated with sperm competition in males and control of fertilization in females. Third, I focus again on P. polionotus and P. maniculatus to examine how mating system influences male response to perceived competition for reproductive success using resident-intruder introductions. I found that while the males of monogamous species were highly aggressive toward rivals, the promiscuous species increased sperm production, which is predicted to increase fertilization success when females mate multiply. Together, this research both characterizes and functionally tests how evolutionary history and social interactions have shaped the diversity in reproductive traits of Peromyscus mice.