Reproductive inequality among males in the genus Pan

Area of Science:

• Primate Behavioral Ecology
• Evolutionary Biology
• Population Genetics

Background:

• Reproductive inequality (skew) is a key driver of natural selection.
• Assessing male reproductive skew is challenging in promiscuous species with slow life histories, like bonobos (Pan paniscus) and chimpanzees (Pan troglodytes).
• Previous studies suggested high male reproductive skew in bonobos, contrary to their egalitarian image.

Purpose of the Study:

• To re-examine male reproductive skew patterns in bonobos and chimpanzees using expanded paternity data.
• To investigate mechanisms influencing male reproductive skew in the genus Pan.
• To compare reproductive skew between bonobos and chimpanzees and identify factors driving differences.

Main Methods:

• Analysis of paternity data from published studies and new data from bonobo and chimpanzee populations.
• Application of the multinomial index (M) to quantify reproductive skew.
• Comparison of observed siring success with predictions from priority-of-access models.

Main Results:

• Considerable overlap in male reproductive skew was observed between bonobos and chimpanzees.
• Bonobos exhibited the highest levels of reproductive skew among the studied populations.
• In two bonobo communities, the highest-ranking male sired more offspring than predicted by priority-of-access, a pattern not seen in chimpanzees.

Conclusions:

• Bonobos demonstrate high male reproductive skew, supported by a broader dataset.
• Reproductive skew models for Pan species must incorporate male-male competition, intergroup dynamics, female grouping, and male-female interactions, including female choice.
• Understanding these factors is crucial for explaining the evolution of inequality in these species.