Testing socially mediated estrous synchrony or asynchrony in wild baboons
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.
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.
KeywordsEstrous synchrony index Female defensibility Female-female competition Ovarian cycle Papio anubis
We thank Craig Packer, Anne E. Pusey, and the Jane Goodall Institute for permitting the use of their long-term data. We are grateful to the Tanzanian agencies of TANAPA, TAWIRI, and COSTECH for allowing research to be conducted in Gombe National Park. We thank Eiiti Kasuya for critical comments on an earlier draft and help during the process of making copies of the original datasheets stored at the University of Minnesota. Finally, we thank the Gombe Stream Research Centre staff for their work of collecting daily observational data. We also thank two anonymous reviewers for constructive comments. This work was supported by Japan Society for the Promotion of Science KAKENHI Grant Numbers 19570230, 23405016 (to AM-O).
Compliance with ethical standards
This study was funded by Japan Society for the Promotion of Science KAKENHI Grant Numbers 19,570,230, 23,405,016 (to AM-O).
Conflict of interest
The authors declare that they have no conflict of interest.
Human and animal rights and informed consent
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. This article does not contain any studies with human participants performed by any of the authors.
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