Variation in female leverage: The influence of kinship and market effects on the extent of female power over males in Verreaux’s Sifaka

Female mammals employ reproductive strategies (e.g., internal gestation)
that result in power asymmetries specific to intersexual dyads. Because
the number of eggs available for fertilization at any given time for most
mammals is quite limited, having a fertilizable egg is potentially an
important source of economic power for females. Control over mating
opportunities is a source of intersexual leverage for female Verreaux’s
sifaka (Propithecus verreauxi). We examined economic factors thought to
influence the value of mating opportunities, and, thus, the extent of
female leverage: kinship and market effects. Using a longitudinal dataset
of agonistic interactions collected during focal animal sampling of all
adult individuals in 10 social groups from 2008-2019, we tested the
effects of relatedness, female parity, reproductive season, and adult sex
ratio (population and group) on (1) the direction of submissive signalling
and (2) which sex won a contested resource. While 96% of the acts of
submission were directed from males towards females, females only won a
third of their conflicts with males. Thus, our study has implications for
evolutionary explanations of female-biased power. If female power evolved
due to their greater need for food and other resources, then intersexual
conflicts would be expected to result in males more consistently
relinquishing control of resources. As expected, males were more likely to
chatter submissively towards successful mothers, during the mating season,
and when the sex ratio was male-biased. Although females generally had
less power to win a conflict when their fertilizable egg was less valuable
(when they were nulliparous or unsuccessful mothers or when interacting
with male kin) and with an increasing female-bias in the sex ratio, this
ability to win additionally was influenced by which sex initiated the
conflict. Our study demonstrates that female leverage can be influenced by
the supply and demand for mating opportunities, but evoking submission
does not translate into winning a resource. Indeed, intersexual power is
dynamic, contextual, and dependent on the individuals in the dyad.