Effects of the Distribution of Female Primates on the Number of Males

Abstract

The spatiotemporal distribution of females is thought to drive variation in mating systems, and hence plays a central role in understanding animal behavior, ecology and evolution. Previous research has focused on investigating the links between female spatiotemporal distribution and the number of males in haplorhine primates. However, important questions remain concerning the importance of spatial cohesion, the generality of the pattern across haplorhine and strepsirrhine primates, and the consistency of previous findings given phylogenetic uncertainty. To address these issues, we examined how the spatiotemporal distribution of females influences the number of males in primate groups using an expanded comparative dataset and recent advances in Bayesian phylogenetic and statistical methods. Specifically, we investigated the effect of female distributional factors (female number, spatial cohesion, estrous synchrony, breeding season duration and breeding seasonality) on the number of males in primate groups. Using Bayesian approaches to control for uncertainty in phylogeny and the model of trait evolution, we found that the number of females exerted a strong influence on the number of males in primate groups. In a multiple regression model that controlled for female number, we found support for temporal effects, particularly involving female estrous synchrony: the number of males increases when females are more synchronously receptive. Similarly, the number of males increases in species with shorter birth seasons, suggesting that greater breeding seasonality makes defense of females more difficult for male primates. When comparing primate suborders, we found only weak evidence for differences in traits between haplorhines and strepsirrhines, and including suborder in the statistical models did not affect our conclusions or give compelling evidence for different effects in haplorhines and strepsirrhines. Collectively, these results demonstrate that male monopolization is driven primarily by the number of females in groups, and secondarily by synchrony of female reproduction within groups.

Variation in grouping patterns, mating systems and social structure: what socio-ecological models attempt to explain

“…Additionally, strepsirrhine primates have recently been found to match the general expectations [45] that as the number of females and/or the overlap in sexual receptivity increases, so too does the number of males per group. Overall, therefore, most primates appear to live in a female defence polygyny system, which is probably the reason that little attention has been paid to potential ecological predictors of mating systems in primates.…”

Constraints and flexibility in mammalian social behaviour: introduction and synthesis

“…The co-occurrence of groups and solitary individuals may reflect an unstable balance between the ecological and social factors generating costs and benefits of living in groups [88], with variation in predation risk and food abundance being the most important factors [85,[89][90][91][92]. Intraspecific variation between groups and pairs [93], or between groups with one or multiple males [94][95][96], can be largely attributed to the outcome of sexual conflict over sex-specific reproductive strategies [97][98][99][100].…”

“…Briefly, because sex differences in potential reproductive rates are particularly pronounced in mammals, males are assumed to maximize their reproductive success by increasing mating opportunities, whereas female reproductive success is more strongly dependent on sufficient access to resources [86,101,102]. Resource distribution and quality, together with predation risk, are therefore the main determinants of female distribution [103], and males then go where the females are [104] and try to monopolize as many of them as possible (which further depends on the temporal distribution of their receptive periods) [100]. If single females are widely spaced out, then individual males will either try to defend access to one (monogamy) or several ( polygyny or promiscuity) of them.…”

Sexual selection and the evolution of behavior, morphology, neuroanatomy and genes in humans and other primates

“…It is no banal conclusion that males follow females (Altmann, 1990). Female distribution then is a major driving factor in determining variation in social and mating systems (Carnes et al, 2011;Lindenfors et al, 2004). Primates have a wide range of mating systems including unusual multimale-multifemale groups (Ostner et al, 2013).…”