Shin Incheol, Hayden Sebastian, Buzatto Bruno A
College of Science and Engineering, Flinders University, Sturt Road, Bedford Park, SA 5042, Australia.
Research Adjunct, Western Australian Museum, 49 Kew Street, Welshpool, WA 6106, Australia.
Evolution. 2025 Sep 12;79(8):1544-1554. doi: 10.1093/evolut/qpaf094.
Aggression can enhance direct fitness by aiding aggressors in securing reproductive resources, but it negatively impacts inclusive fitness when directed toward kin. We investigated the trade-off between the indirect fitness costs of aggression among kin and the direct benefits of increased success in mate competition using the bulb mite Rhizoglyphus echinopus, a male dimorphic species in which male fighters kill rivals with their modified third legs, while unmodified male scramblers seek unguarded females to mate. Our experiments showed that fighter aggression was never directed toward females, suggesting that fighter aggression evolved as a tactic to monopolize mates. Fighters grab other males before killing them, and grabbing behavior increased in the presence of a female, regardless of the presence of kin. Scrambler mortality increased with fighters' grabbing activity. Whereas the presence of mate competition increased lethal aggression, kinship decreased it, as higher mortality was observed among nonkin. These findings suggest that aggressive behavior intensifies under mate competition, but the decision to escalate aggression to lethal levels is influenced by kinship. In conclusion, this study provides insight into the trade-offs underlying kin-discriminatory aggression and direct benefits.
攻击行为可以通过帮助攻击者获取繁殖资源来提高直接适合度，但当针对亲属时，它会对广义适合度产生负面影响。我们使用球螨（Rhizoglyphus echinopus）来研究亲属间攻击行为的间接适合度成本与交配竞争中成功增加的直接益处之间的权衡，球螨是一种雄性二态性物种，其中雄性格斗者用其特化的第三条腿杀死对手，而未特化的雄性投机者则寻找未设防的雌性进行交配。我们的实验表明，格斗者的攻击行为从不针对雌性，这表明格斗者的攻击行为是作为一种垄断配偶的策略而进化出来的。格斗者在杀死其他雄性之前会抓住它们，并且在有雌性在场的情况下，无论是否有亲属在场，抓取行为都会增加。投机者的死亡率随着格斗者抓取活动的增加而增加。虽然交配竞争的存在会增加致命攻击，但亲属关系会降低致命攻击，因为在非亲属中观察到更高的死亡率。这些发现表明，攻击行为在交配竞争中会加剧，但将攻击升级到致命程度的决定受到亲属关系的影响。总之，这项研究为亲属歧视性攻击行为和直接益处背后的权衡提供了见解。
