Paternity and kin structure among neighbouring groups in wild bonobos at Wamba

Abstract

Although both bonobos and chimpanzees are male-philopatric species, outcomes of male–male reproductive competition seem to be more closely associated with mating success in chimpanzees. This suggests that the extent of male reproductive skew is lower in bonobos. In addition, between-group male–male reproductive competition is more lethal in chimpanzees. This suggests that between-group differentiation in male kinship is lower in bonobos. We analysed the paternity of 17 offspring in two bonobo groups and estimated the relatedness of individuals among three neighbouring groups by using DNA extracted from non-invasive samples at Wamba, in the Democratic Republic of the Congo. The alpha males sired at least nine of 17 offspring. This supports a previous finding that the male reproductive skew is higher in bonobos than that in chimpanzees. Average relatedness among males within groups was significantly higher than that among males across groups, whereas there was no significant difference among females between within and across groups. These results are consistent with male philopatry, highly skewed reproductive success of males and female dispersal. Higher average relatedness among males within groups suggest that the differences in hostility towards males of different groups between bonobos and chimpanzees may be explained by factors other than kinship.

Inter‐group aggressive interaction patterns indicate male mate defense and female cooperation across bonobo groups at Wamba, Democratic Republic of the Congo

“…Compared to the other males, the alpha‐male had an exceptionally high aggression frequency toward out‐group individuals (Figure ). Together with the fact that the alpha‐male possessed very high reproductive success (sired 4 out of 7 infants who had been born in the PE group between 2011 and 2014, whereas the second successful males sired one infant each; Ishizuka et al, ), this result provides further support to the prediction that males with high reproductive success behave more aggressively toward out‐group individuals. The increase in the cooperation with within‐group members to attack out‐group individuals was not uniform, but larger in males than in females.…”

“…In addition, chimpanzee males who are more sexually coercive to females possess higher reproductive success (Muller, Kahlenberg, Thompson, & Wrangham, : Muller, Thompson, Kahlenberg, & Wrangham, ; Kaburu & Newton‐Fisher, ; Feldblum et al, ). In bonobos, higher ranking males also have higher reproductive success, but male bonobos do not compete severely over social ranking: males seldom form coalitions within a group, and seldom injure their opponent (Surbeck et al, , c; Ishizuka et al, ; this study). Studies suggest that a male bonobo's social ranking and mating success are largely influenced by support from their mother and female mate choice rather than by direct competition among males (Furuichi, ; Surbeck et al, , ; Surbeck, Deschner, Schubert, Weltring, & Hohmann, ).…”

“…Male bonobos behaved aggressively toward out‐group individuals more frequently than females did, and these aggressive interactions mostly targeted males. Additionally, higher‐ranking individuals, with higher reproductive success (Ishizuka et al, ; Surbeck, Langergraber, et al, ), directed aggression toward out‐group individuals more frequently than lower‐ranking males. Compared to the other males, the alpha‐male had an exceptionally high aggression frequency toward out‐group individuals (Figure ).…”

“…This might lower the male monopolization potential of females and make males invest less in female defense, which might lead to moderate male competition (Furuichi, , ). Nonetheless, status hierarchies among males are usually linear and steep (Stevens et al, ; Surbeck, Mundry, & Hohmann, ; Tokuyama & Furuichi, ), with higher‐ranking males siring more offspring than lower‐ranking males (Ishizuka et al, ; Surbeck, Langergraber, Fruth, Vigilant, & Hohmann, ).…”

Tolerance in intergroup encounters: Payoffs and plasticity in non-human primates and humans

“…Primate individuals use a variety of strategies in intergroup encounters, from aggression to 33 tolerance; however, recent focus on the evolution of either warfare or peace has come at the 34 cost of characterizing this variability. We identify evolutionary advantages that may incentivize 35 tolerance toward extra-group individuals in humans and non-human primates, including 36 enhanced benefits in the domains of transfer and mating, food acquisition, inclusive fitness, and 37 repeated interactions with an extra-group member.…”