Thesis

Examination of precopulatory and postcopulatory sexual selection mechanisms in the American black bear, Ursus americanus

Most extant bear species are threatened or endangered. One of the species not endangered, the American black bear (Ursus americanus), provides a practical reproductive model that can be applied to the conservation of other ursid species, due to their high abundance and similar reproductive biology. This thesis contains detailed information regarding precopulatory and postcopulatory sexual selection in this species. Specifically, female mate choice, sperm competition, and the possibility of cryptic female choice are examined. This is the first study able to thoroughly examine these reproductive strategies in bears, through the use of an experimental setup. Chapter 1 is comprised of an introduction, experimental aims, and hypotheses. In chapter 2, we demonstrate that females do not select mates based upon morphological traits or social status, and provide evidence indicating that females may use cryptic female choice. Chapter 3 discusses the implications of the results for management of captive and wild bears. We quantified successful mounts (those that resulted in ejaculation), unsuccessful mounts, quivering durations (a proxy for ejaculation quantity), paternity assessment of embryos, and breeding order of males. Our results indicate that large, prime-age, dominant males were not as strongly selected for as mates as would be expected in the wild. Additionally, males that sired embryos did not ejaculate more than non-sires, which is the opposite trend that would be expected in the presence of sperm competition. In fact, the prenatal reproductive success of large, prime, dominant males was significantly less than the postnatal reproductive success of these same types of males in the wild, further calling into question the hypothesis that black bears solely use sperm competition. Our results suggest the need for reevaluation of pre- and postcopulatory sexual selection in black bears.

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