Testing socially mediated estrous synchrony or asynchrony in wild baboons

Abstract

Abstract: Social structure of animal groups is affected by the spatial and temporal distribution of females. In particular, the extent to which fertile periods of females are temporally overlapped has been deemed as a crucial factor to determine the structure of social groups in primate species. Dominant males are less able to monopolize fertile females when there are more females being in estrous simultaneously. This provides a potential opportunity for females to manipulate their defensibility by dominant males by modifying the level of estrous overlap. Previous studies that have attempted to detect socially mediated synchrony or asynchrony of estrous cycles have produced mixed results, some of which have been questioned on methodological grounds. Here, we address this issue using an exceptionally large dataset of daily reproductive states in four troops of wild anubis baboons (Papio anubis) over 14 to 24 years (77 troop-years). We compare observed levels of estrous synchrony with null distributions obtained by a randomization procedure under the assumption that estrous cycles are mutually independent among females in the same troop. We do not find any evidence supporting synchrony or asynchrony of estrous cycles. Based on our result and those of previous studies in other species of baboons, we conclude that socially mediated synchrony or asynchrony is unlikely to play a significant role in structuring social groups in baboons. In addition, our analysis points out that care should be taken when applying randomization procedures to a dataset with missing observations. Significance statement: Females in some animal species have been suggested to synchronize or desynchronize their estrus cycles. This phenomenon may have a significant impact on the structure of animal societies because when there are more females simultaneously in estrus, even a dominant male is less able to defend them from other males. Previous attempts to detect non-random estrous cycles in primates have produced mixed results, and some of them have been criticized on the methodological grounds. We investigate whether wild female anubis baboons exhibit non-random estrous cycles using a larger dataset than previous studies. For a statistical analysis, we use a randomization procedure, taking a biasing effect of missing observations into consideration. Consistent with earlier studies on other species of baboons, our analysis does not find any evidence supporting estrous synchrony or asynchrony in anubis baboons.