The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


The Influence of Fighting Ability and Reproduction in Intersexual Relationships in Verreaux’s Sifaka (Propithecus verreauxi)

KATHRYN M. ORTIZ and REBECCA J. LEWIS.

Department of Anthropology, University of Texas Austin

March 26, 2015 10:30, Grand Ballroom E/F/G Add to calendar

The base of power in dyadic relationships can be difficult to isolate. Investigating the ontogeny of power may untangle how dominance and leverage shape intersexual relationships, especially in “female-dominant” species. Our goal was to test the alternative hypotheses that direction of agonism in intersexual dyads is predicted by (1) differences in fighting ability (i.e. dominance), or (2) females reaching reproductive maturity (i.e. leverage). Behavior and morphometric data were collected from 2007-2012 from 23 adults and subadults from 4 social groups of Verreaux’s sifaka (Propithecus verreauxi) in Kirindy Mitea National Park. Contrary to the hypothesis that female power is based on dominance, dyadic differences in body mass and canine size did not significantly predict submission or aggression: smaller females elicited unidirectional submissive signals from, and directed aggression towards, adult males. Consistent with the leverage hypothesis, age significantly predicted submission: adult females received 100% of submissive signals from males, whereas subadult females emitted 97%. While male-to-female aggression was not predicted by age, a trend existed for adult females to initiate aggression towards males more frequently than subadult females. The ontogeny of intersexual power in sifaka reflects changes in reproductive abilities rather than differences in size, suggesting that intersexual power in sifaka is based on leverage rather than dominance. Interestingly, female leverage seems to be based on the ability to produce offspring rather than mating opportunities because subadult female sifaka can sometimes be sexually active. Moreover, our results suggest that leverage effects may be more important in determining intersexual power than fighting ability.