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

Abstract

Summary In 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.

Correlates of individual participation in boundary patrols by male chimpanzees

“…Instead, all Kasekela males participated in at least half of all boundary patrols. Recent paternity analysis at Gombe indicate that the alpha male obtains a disproportionate share of paternities in Kasekela [53]. Despite these reproductive benefits, current and former alpha males did not patrol at significantly higher rates than other males.…”

“…The estimates for periphery visits closely resembled those for boundary patrols Mating frequency is admittedly an imperfect measure of reproductive success, given that chimpanzees mate promiscuously. Given that only alpha males obtain a disproportionate share of paternities [53], we compared patrol participation rates for current and former alpha males with those of males that never reached top rank. However, the patrol participation rate for current and former alpha males (mean = 75 ± 3%, N = 8) did not differ significantly from that of males who had never reached alpha status (70 ± 3%, N = 15; binomial regression, β = 0.11, z = 1.00, p = 0.32).…”

“…In the long term, if males continue to sire offspring, older males should have more offspring. High-ranking males sire more offspring [52], although recent analysis indicates that only the highest-ranking males (alphas) sire a disproportionate share [53].…”

The Creative Neurons

“…Our potential for flexible coalitions and alliances is exceptional (e.g., Chagnon, 1988 ; Choi and Bowles, 2007 ; cf. Fragaszy and Visalberghi, 1990 ; Bissonnette et al, 2015 ; Vale et al, 2021 ), and has deep evolutionary roots ( Wrangham, 1999 ; Leblanc, 2003 ; Churchill et al, 2009 ; Feldblum et al, 2021 ). The origins are posited to involve unusual aspects of human family relationships—stable breeding bonds and fathering, brother-sister bonds, grandparenting, bilateral kin bonds, affinal bonds—that facilitate interaction among individuals residing in different groups and thereby kindle cumulative culture ( Alexander, 1979 ; Hrdy, 1981 ; Chapais, 2008 ; Flinn, 2017 ).…”

An intentional cohesion call in male chimpanzees of Budongo Forest

“…Bonding in male chimpanzees is important for a variety of activities and serves as a basis for trust and support during dangerous activities, such as intergroup aggression (Herbinger et al 2009;Wilson et al 2014), cooperative hunting (Hobaiter et al 2017), predator defence (Boesch 1991) and intragroup conflicts (Goodall 1986;Mitani 2009;Muller and Mitani 2005). Generally, associating with highranking males can also be advantageous and bring fitness benefits, such as higher reproductive success (Bray et al 2016;Duffy et al 2007;Feldblum et al 2021;Kaburu and Newton-Fisher 2015).…”