Mating behavior and factors influencing paternity in a semi-free ranging population of American black bears, Ursus americanus

Captive breeding programs and wildlife managers are challenged with maintaining bear populations, including the six (of eight) species that are endangered or threatened. Therefore, the need for complete and thorough information on bear mating behavior is critical. While black bears are not endangered, they provide a model from which to learn valuable information that can be applied to other species.\ud The thesis presented herein contains the most comprehensive documentation on each stage of the consummatory phase of mating behavior in American black bears, Ursus americanus. In addition, it includes preliminary data on factors that potentially influence paternity in this species. Chapter 1 provides an overall introduction and the hypotheses. In chapter 2, we quantify each stage of the consummatory phase of mating behavior and provide evidence that male American black bears are using chemosensory signals to assess a female???s estrous state. Chapter 2 is a complete ???stand-alone??? document that will be submitted for publication. We present our preliminary paternity results in chapter 3 and discuss what these suggest about how black bears may be using male body size, induced ovulation and sperm competition as sexual selection strategies. In addition, we provide evidence that female American black bears are fertile in more than one of their multiple estruses.\ud We documented 139 mounts (14 successful and 125 unsuccessful). Successful mounts, those that included quivers (ejaculation), were significantly longer in duration (~30-fold) than unsuccessful mounts. We used two indicators of estrus: physiological (average vulva score) and behavioral (bouts of successful mating). Physiological and behavioral estrus overlapped in that all successful mounts occurred when females had an average vulva score of ???2. Our data suggest that males are using chemosensory cues to assess the estrous state of a female; 77% of successful mounts were preceded by anogenital investigation. Further, females may be using chemosensory cues to synchronize estrus; only 1 in 5 females exhibited physiologic estrus independently of the others.\ud Bears are assumed to employ sperm competition as a sexual selection strategy. One component of sperm competition is the relative amount of sperm deposited in the female???s reproductive tract. We compared intromission duration, intromission frequency, quiver duration and quiver frequency between sires and non-sires; there was no significant difference in these behavioral measures (p???0.55). However, one of our three females was mated by both sire (two times) and non-sire on the same day. Combining the sire???s 2 successful mounts resulted in a longer quiver duration (~1.5-fold), a higher quiver frequency (~1.5-fold), and most likely a higher proportion of sperm deposition. Therefore, this male may have employed sperm competition.\ud Female American black bears are polyestrus; however, it is unknown if each of these estruses is conceptive. One of our three females conceived in estrus 1 yet still entered a second estrus. Thus, our results provide evidence that conception is not restricted to a female???s last estrus.\ud Previous paternity studies suggest that larger, more mature males sire the majority of offspring. One of our three litters is consistent with these findings. One involved a sire and non-sire that were relatively close in size. The other was sired by the smaller, more immature male. Thus, our data are inconclusive regarding male body size and its effect on paternity.\ud We began to investigate the legitimacy of some sexual selection hypotheses that have been assumed to be true of bears. At the same time, we experimented with a novel technique, the Experion micro-fluidic chip, to determine its usefulness in paternity analysis. This study provides the platform for potentially using this tool to collect empirical data on bear paternity as a means for answering the following question: which strategies, both pre-and post-copulatory, do male and female black bears use to determine paternity?Biological Science