Sex-specific association patterns in bonobos and chimpanzees reflect species differences in cooperation

Abstract

In several group-living species, individuals' social preferences are thought to be influenced by cooperation. For some societies with fission–fusion dynamics, sex-specific association patterns reflect sex differences in cooperation in within- and between-group contexts. In our study, we investigated this hypothesis further by comparing sex-specific association patterns in two closely related species, chimpanzees and bonobos, which differ in the level of between-group competition and in the degree to which sex and kinship influence dyadic cooperation. Here, we used long-term party composition data collected on five chimpanzee and two bonobo communities and assessed, for each individual of 10 years and older, the sex of its top associate and of all conspecifics with whom it associated more frequently than expected by chance. We found clear species differences in association patterns. While in all chimpanzee communities males and females associated more with same-sex partners, in bonobos males and females tended to associate preferentially with females, but the female association preference for other females is lower than in chimpanzees. Our results also show that, for bonobos (but not for chimpanzees), association patterns were predominantly driven by mother–offspring relationships. These species differences in association patterns reflect the high levels of male–male cooperation in chimpanzees and of mother–son cooperation in bonobos. Finally, female chimpanzees showed intense association with a few other females, and male chimpanzees showed more uniform association across males. In bonobos, the most differentiated associations were from males towards females. Chimpanzee male association patterns mirror fundamental human male social traits and, as in humans, may have evolved as a response to strong between-group competition. The lack of such a pattern in a closely related species with a lower degree of between-group competition further supports this notion.

Novelty Response of Wild African Apes to Camera Traps

“…We tentatively propose that these results can be best explained by the leadership hypothesis [23,24,26]. The co-dominance between the sexes and high degree of female gregariousness in bonobos [25] may contribute to the lack of a defined leader and explain why bonobos were, on average, the most neophobic of the three great apes. A recent study on leadership in wild bonobos found that multiple older females were central to group movement decisions [36].…”

“…Additionally, the leadership hypothesis, initially proposed for schools of fish [23], suggests that in species lacking a clear leader (i.e., egalitarian), individual personalities strongly predict group decisions about where to feed and rest [16,24]. The allocation of risk is predicted to be spread more evenly within the group in more egalitarian species, such as bonobos [25], rather than resting solely on one or a few dominant individuals, as in gorillas and chimpanzees [26]. Captive experiments have shown that bonobos are more neophobic and risk-averse than chimpanzees or orangutans and exhibit novelty responses more similar to those of human children [7,8].…”

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

“…They live in male‐philopatric multi‐male/multi‐female groups with stable memberships, which may split into temporary “parties” (fission–fusion grouping patterns, Kano, ; Sakamaki et al, ). Unlike other species, in which individuals of the philopatric sex usually have stronger association, affiliative, and cooperative relationships than the dispersing sex, association and affiliative behaviors in bonobos are more frequently observed among females, except for mother–offspring pairs (Furuichi, ; Moscovice et al, ; Surbeck et al, ; White, ). Male bonobos rarely form coalitions, but the females often form coalitions to attack the males, which may lead to within‐group high social status for the females (Parish, ; Surbeck & Hohmann, ; Tokuyama & Furuichi, ).…”

<NOTE>A case of maternal response towards dead offspring in wild bonobos: Staring, grooming but not carrying

“…Although the number of available data is still scarce, duration of maternal carriage of their dead offspring may be longer in chimpanzees than in bonobos. This may be because female bonobos are more social than female chimpanzees (Kano 1992;Furuichi 2009;Surbeck et al 2017). Mother bonobos may choose to leave their dead offspring in order to perform intense social interactions with other alive conspecifics.…”