Attractiveness of female sexual signaling predicts differences in female grouping patterns between bonobos and chimpanzees

Surbeck and colleagues investigate the proximate drivers of female gregariousness in bonobos and chimpanzees across different observed communities. Their findings indicate that varied levels of sexual signalling in these two species result in different social behaviours regarding female grouping and potentially cooperation. Here we show that sexual signaling affects patterns of female spatial association differently in chimpanzees and bonobos, indicating its relevance in shaping the respective social systems. Generally, spatial association between females often mirrors patterns and strength of social relationships and cooperation within groups. While testing for proposed differences in female-female associations underlying female coalition formation in the species of the genus Pan, we find only limited evidence for a higher female-female gregariousness in bonobos. While bonobo females exhibited a slightly higher average number of females in their parties, there is neither a species difference in the time females spent alone, nor in the number of female party members in the absence of sexually attractive females. We find that the more frequent presence of maximally tumescent females in bonobos is associated with a significantly stronger increase in the number of female party members, independent of variation in a behavioural proxy for food abundance. This indicates the need to look beyond ecology when explaining species differences in female sociality as it refutes the idea that the higher gregariousness among bonobo females is driven by ecological factors alone and highlights that the temporal distribution of female sexual receptivity is an important factor to consider when studying mammalian sociality.

Automated summary

The study by Surbeck and colleagues investigates the differences in female social behavior and cooperation patterns between bonobos and chimpanzees, highlighting the impact of sexual signaling on shaping the respective social systems. They found that the spatial association between females reflects social relationships and cooperation within groups, with limited evidence supporting higher female-female gregariousness in bonobos. The presence of maximally tumescent females in bonobos is associated with a significantly stronger increase in the number of female party members, suggesting that factors beyond ecology play a role in female sociality differences between these species.