DOI: 10.5061/dryad.ngf1vhhwh
title: Variation in female leverage: The influence of kinship and market effects on the extent of female power over males in Verreaux’s Sifaka

description: 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.
description: We collected all occurrences of
 intragroup agonistic intersexual interactions during 1-hour focal animal
 sampling sessions (Altmann 1974) of all adult and subadult sifaka, for a
 total of approximately 14,000 hours of observation from 2008 through 2019.
 Insufficient behavioral and demographic data were available for 2009-2010
 because Cyclone Fanele interrupted data collection and thus were excluded
 from our analysis. The identity of the initiator and of the receiver was
 recorded for each interaction, and all behaviors occurring during the
 interaction were recorded as occurring either in isolation or as part of a
 sequence. Agonistic behaviors were defined according to the Brockman
 (1994) ethogram with the following additions: “food rob +” (X tries to
 take the food away from Y and is successful), “food rob –” (X tries to
 take the food away from Y and is unsuccessful), and “snap at” (X bites in
 the direction of Y but does not make contact). In addition, “proximity” (a
 concept implicit to the definition of certain behaviors) was defined as
 occurring when individuals were within 1 m of each other (Lewis
 2019). For all agonistic
 encounters, we scored an individual as “winning” a conflict if the other
 individual in the dyad moved at least 1 m away from the “winner” within 10
 seconds of the agonistic interaction. Note that we did not limit our
 analysis of “winning” to the feeding context because sifaka compete for
 other resources in addition to food (e.g., water, space, sun, shade,
 grooming partners, huddling partners). Moreover, our definition of a “win”
 included a broader set a behaviours than merely “supplant” (X moves toward
 Y, Y immediately changes location [within 5 seconds], X occupies the
 location previously held by Y: cf. Brockman 1994)). If neither individual
 withdrew after the agonistic interaction, neither individual was
 considered the winner and the outcome was scored as “neutral”. The one
 exception to this rule was for the “food rob” behaviors because “food rob
 +” is defined as an initiator successfully gaining control of the food
 resource, while “food rob –” necessarily means that the initiator was not
 successful. Therefore, the identity of the sifaka that had control of the
 food resource at the end of the “food rob” behavior was scored as the
 winner. Sifaka often exhibit multiple aggressive and/or
 submissive behaviors within an agonistic interaction. We thus used the
 following rules for scoring an interaction as “win” versus “neutral” when
 multiple behaviors occurred in a sequence. If a social interaction began
 with an approach, the 10 second rule started with the time of the first
 non-approach agonistic behavior. If an individual used multiple types of
 aggressive behaviors essentially simultaneously (e.g., lunge and cuff),
 then we only scored the first aggressive act. However, if an individual
 used repeated, successive acts of aggression towards another individual
 (e.g., three cuffs within 10 seconds) and the receiver chattered
 submissively immediately after each individual aggressive act (e.g., cuff
 then chatter response, cuff then chatter response, cuff then chatter
 response), we scored each aggressive act independently, with the
 assumption that the additional acts of aggression were needed because the
 first aggressive act was not successful. When animals repeatedly made a
 submissive chatter vocalization spontaneously (i.e., without receiving
 aggression within 10 sec beforehand), we scored the agonistic events as
 independent when there was at least 5 seconds between the end of the first
 chatter and the beginning of the second chatter. To address the issue that
 these repeated aggressive or submissive acts are not entirely independent
 of one another, we assigned a corresponding proximity “bout identity” to
 each agonistic act and then used bout ID as a random factor in our
 statistical models. A proximity bout was defined as a period of time in
 which the members of a dyad were continuously within 1 m of each other
 within a given 1-hr focal sample, and all behaviors occurring during this
 period were assigned with the same bout ID. Finally, for each agonistic
 interaction, we also scored the identity of the initiator of the
 interaction. Note that by definition, the winner of an interaction was
 always scored as the initiator for supplants. We conducted monthly censuses of the
 population in the Ankoatsifaka grid system of trails (Leimberger &
 Lewis 2017; Lewis et al. 2020). In addition to locating all groups with
 radio collars and recording the identity of each individual present in the
 group, we located unmarked groups and solitary individuals by walking the
 trail system. While sifaka live in cohesive groups, they sometimes visit
 other groups, and males occasionally roam independently during the mating
 season (Richard et al. 1993; Brockman 1999; Leimberger & Lewis
 2017). On the rare occasions when a known individual was not observed on
 the day of the census, we nonetheless retroactively added them to the
 census data for that month if the individual was observed during
 behavioral data collection within seven days of the census.