Effects of body size on male mating tactics and paternity in black bears,Ursus americanus

Abstract

The reproductive behaviour of large, solitary mammals is difficult to study. Owing to their secretive nature and wide-ranging habits, aspects of male mating behaviour are poorly documented in solitary than in social species. We used radiotelemetry and microsatellite DNA analysis to investigate the influence of body size on male mating tactics and short-term reproductive success in the black bear, Ursus americanus, a solitary carnivore. We investigated male ranging behaviour and documented male encounters with breeding females to determine whether males employed conditional mating tactics according to their body sizes. We found that male home-range sizes were not positively associated with body size, but encounter rates with breeding females were. Although all males searched widely for females, mating access appeared to be largely determined by fighting ability. Large males encountered more breeding females and had more frequent encounters during the females' estimated receptive periods than did small-and medium-sized males. Paternity was highly skewed toward the three dominant males who fathered 91% of the cubs sampled during the 3-year study. Paternity was correlated with the frequency of male encounters during female receptive periods. Male encounters, however, overestimated the success of medium-sized males and underestimated the overall variance in male reproductive success. Multiple paternity occurred in two of seven litters, indicating that sperm competition is important in black bear mating behaviour. Implications for male lifetime reproductive success are discussed.Résumé : Le comportement reproducteur de grands mammifères solitaires est difficile à étudier. À cause de la nature discrète et des habitudes nomades des mâles des espèces solitaires, plusieurs aspects de leur comportement reproducteur sont beaucoup moins bien connus que chez les espèces sociales. Nous avons utilisé la radiotélémétrie et l'analyse des microsatellites de l'ADN pour étudier l'influence de la taille du corps sur les tactiques d'accouplement du mâle et sur le succès à court terme de la reproduction chez l'ours noir, Ursus americanus, un carnivore solitaire. Nous avons déterminé les comportements de déplacement des mâles et analysé les rencontres des mâles avec des femelles en état de reproduction pour voir si les mâles utilisent des tactiques conditionnelles d'accouplement en fonction de leur taille. Les surfaces des domaines vitaux des mâles ne sont pas en corrélation positive avec leur taille corporelle, mais leurs taux de rencontre de femelles le sont. Bien que tous les mâles fassent des recherches à grande échelle pour trouver des femelles, l'accès aux femelles semble être largement déterminé par leur capacité de lutte. Les grands mâles rencontrent plus de femelles reproductrices et font plus de contacts durant les périodes apparemment réceptives des femelles que ne le font les mâles de petite et moyenne tailles. La paternité est fortement asymétrique et est le fait principalement de trois mâles qui ont engendré 91 % des ourson...

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