Social bonds provide multiple pathways to reproductive success in wild male chimpanzees

Joseph T Feldblum,Christopher Krupenye,Joel Bray,Anne E Pusey,Ian C Gilby

doi:10.1016/j.isci.2021.102864

Abstract

SummaryIn most male mammals, fitness is strongly shaped by competitive access to mates, a non-shareable resource. How, then, did selection favor the evolution of cooperative social bonds? We used behavioral and genetic data on wild chimpanzees (Pan troglodytes schweinfurthii) in Gombe National Park, Tanzania, to study the mechanisms by which male-male social bonds increase reproductive success. Social bonds increased fitness in several ways: first, subordinate males that formed strong bonds with the alpha male had higher siring success. Independently, males with larger networks of strong bonds had higher siring success. In the short term, bonds predicted coalition formation and centrality in the coalition network, suggesting that males benefit from being potential allies to numerous male rivals. In the long term, male ties influenced fitness via improved dominance rank for males that attain alpha status. Together, these results suggest that male bonds evolved in chimpanzees by affording both short- and long-term pathways to reproductive success.

Highlights

Humans and other animals form differentiated affiliative bonds that are associated with survival and reproduction (Holt-Lunstad et al, 2010; Ostner and Schulke, 2018; Seyfarth and Cheney, 2012)
Did selection favor the evolution of cooperative social bonds? We used behavioral and genetic data on wild chimpanzees (Pan troglodytes schweinfurthii) in Gombe National Park, Tanzania, to study the mechanisms by which male-male social bonds increase reproductive success
Bonds predicted coalition formation and centrality in the coalition network, suggesting that males benefit from being potential allies to numerous male rivals

Summary

Introduction

Humans and other animals form differentiated affiliative bonds that are associated with survival and reproduction (Holt-Lunstad et al, 2010; Ostner and Schulke, 2018; Seyfarth and Cheney, 2012). Male affiliative behavior can predict coalitionary support in aggressive interactions (Mitani, 2006; Watts, 2002), and subordinate males with higher direct and indirect centrality in the aggressive coalitions network have higher current and future rank (Gilby et al, 2013; Watts, 2018) and are more likely to sire offspring in the short term, independent of dominance rank (Gilby et al, 2013). We tested three hypotheses regarding the mechanisms linking sociality and paternity success These were that (1) subordinate males can form strong bonds with the alpha male to achieve greater reproductive success via mating concessions, which we call the ‘‘alpha concessions’’ hypothesis; (2) males can form bonds with other males to improve their short-term reproductive success via social leverage stemming from aggressive coalitionary support, which we call the ‘‘coalitionary support’’ hypothesis; and (3) males can form bonds with other iScience 24, 102864, August 20, 2021 a 2021 The Authors.

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