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Why bonobos show a high reproductive skew towards high-ranking males: analyses for association and mating patterns concerning female sexual states

A Correction to this article was published on 01 September 2022

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Abstract

Among non-human primates, male dominance rank is not necessarily a good indicator of mating success, and relationships between male dominance rank and mating or reproductive success are affected by female behavior and sexual states implying their probability of conception. Although comparisons of the behavior of male chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) suggest that the effect of male dominance rank on mating success is expected to be less prominent in bonobos, recent genetic studies have shown that high-ranking male reproductive skew is higher in bonobos than in chimpanzees. One possible reason for the higher reproductive skew in bonobos could be that female behavior and their sexual states may have much more influence on male mating and reproductive success in bonobos than in chimpanzees. In the current study on bonobos, we conducted focal animal observation of females and analyzed the influence of female sexual swelling, the number of days after parturition, and dominance rank of males on female associations, and copulation with adult males. Our results showed that females with maximum swelling (MS) had more proximity with high-ranking males and copulated more frequently with higher-ranking males than with lower-ranking males. Females for whom longer time had elapsed since parturition, and therefore had higher probabilities of conception, had 5-m proximity with adult males more frequently than females whom shorter time had elapsed since parturition, but did not have more copulation with adult males. Females with MS had proximity and copulated with high-ranking males frequently, which partly explains why the reproductive skew is so high in bonobos. These results are discussed in relation to previous hypotheses on the influence of long-lasting mother–son relationships on mating success of males and on the contribution of female receptivity during non-conceptive nursing periods to moderate intermale aggression in bonobos.

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Acknowledgments

We thank the Research Center for Ecology and Forestry and the Ministry of Scientific Research, DRC. We also thank members of the Ecology and Social Behavior section of the Primate Research Institute, Kyoto University, for their helpful advice, and our research assistants at Wamba for their great help during the bonobo observations. We thank Ms. Keiko Mouri and Dr. Chie Hashimoto for helping with our hormonal analysis. We are grateful to Mr. Shohei Shibata, Dr. Shintaro Ishizuka, Dr. Kazuya Toda, Dr. Heungjin Ryu, Dr. Nahoko Tokuyama, and Dr. Tetsuya Sakamaki, for providing valuable information, contributing to the continuous observation of the study group and camp management at Wamba.

Funding

This study was supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (26257408, 16H02753, and 18KK0204 to Yokoyama).

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Correspondence to Takumasa Yokoyama.

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Yokoyama, T., Furuichi, T. Why bonobos show a high reproductive skew towards high-ranking males: analyses for association and mating patterns concerning female sexual states. Primates 63, 483–494 (2022). https://doi.org/10.1007/s10329-022-01004-1

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  • DOI: https://doi.org/10.1007/s10329-022-01004-1

Keywords

  • Pan paniscus
  • Mating pattern
  • Reproduction
  • Sexual states