Female Power in Verreaux’s Sifaka (Propithecus verreauxi) Is Based on Maturity, Not Body Size

Abstract

Conflicts between individuals are common among animals, with power dynamics often biased toward a particular sex. However, individuals across species exert power differently depending on the primary source of that power. Dominance-based power depends on fighting ability (e.g., greater body size) whereas leverage-based power depends on resources that cannot be taken by force (e.g., mating opportunities). Both can change in relative importance during development. We examined the development and base of female-biased power structures in Verreaux’s sifaka (Propithecus verreauxi) by analyzing the effects of reproductive maturity and body mass on intersexual conflict outcomes. We used data on four social groups at Ankoatsifaka Research Station in Kirindy Mitea National Park collected from 2007 to 2016, which included 483 decided agonistic encounters with both behavioral and morphometric data available. We used generalized linear mixed models to examine the effects of age, body mass, and female reproductive maturity on conflict outcome. Power relationships between mature females and males were unambiguously female biased. Female reproductive maturity, and not body mass, predicted intersexual conflict outcomes. Once reproductively mature, females almost never lost to males, except when females had not yet had an infant survive past weaning. Our results are thus consistent with the hypothesis that female leverage characterizes social structures of adult Verreaux’s sifaka more than female dominance. Future studies are needed to explore the influence of other sources of leverage and dominance, however. Similar studies in other primate species will clarify the role of what is often called “dominance” but may actually be leverage-based power.