ゴリラの個人的な状況は、同群の仲間に対する攻撃性に影響を与える(Gorillas’ personal circumstances shape their aggression towards groupmates)

2025-07-25

2025-07-24 マックス・プランク研究所

マックス・プランク進化人類学研究所とトゥルク大学の研究チームは、野生のゴリラ31頭を対象に25年間観察したデータを分析。個体の妊娠・授乳などの生理的状態や群内の雌雄構成により、攻撃行動の相手が変化することが判明しました。妊娠中の雌は高リスクな相手にも攻撃を仕掛け、授乳中の雌もエネルギー需要のため攻撃的になりますが、子の安全に配慮して控えめな行動も見られます。群内の雄の数が多いと高ランク個体への攻撃が増加し、雌が多い群ではより安全な低ランク個体が標的となる傾向がありました。攻撃行動は状況に応じた戦略的選択であることが示唆されます。

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リスクを取るインセンティブはメスのゴリラの攻撃的行動を予測する Risk-taking incentives predict aggression heuristics in female gorillas

Nikolaos Smit,Martha M Robbins
eLife Published:July 23, 2025
DOI:https://doi.org/10.7554/eLife.107093.2

Abstract

Competition is commonly reflected in aggressive interactions among groupmates, as individuals try to attain or maintain higher social ranks that can offer them better access to critical resources. In this study, we investigate the factors that can shift competitive incentives against higher- or lower-ranking groupmates, that is, more or less powerful individuals. We use a long-term behavioural dataset on five wild groups of the two gorilla species starting in 1998, and we show that most aggression is directed from higher- to lower-ranking adult females close in rank, highlighting rank-reinforcement incentives. Yet, females directed 42% of aggression to higher-ranking females than themselves. Females targeted groupmates of higher rank with increasing number of males in the group, suggesting that males might buffer female-female aggression risk. Contrarily, they targeted females of lower rank with increasing number of females in the group, potentially because this is a low risk option that females prefer when they have access to a larger pool of competitors to choose from. Lactating and pregnant females, especially those in the latest stage of pregnancy, targeted groupmates of higher rank than the groupmates that cycling females targeted, suggesting that energetic needs may motivate females to risk confrontation with more powerful rivals. Our study provides critical insights into the evolution of competitive behaviour, showing that aggression heuristics, the simple rules that animals use to guide their aggressive interactions, are not simply species-specific but also dependent on the conditions that populations and individuals experience.