Reproductive conflict resolution in cooperative breeders

Female infanticide is common in animal societies where groups comprise multiple co-breeding females. To reduce the risk that their offspring are killed, mothers can synchronize breeding and pool offspring, making it hard for females to avoid killing their own young. However, female reproductive conflict does not invariably result in reproductive synchrony, and we lack a general hypothesis explaining the variation in conflict resolution strategies seen across species. Here, we investigate the fitness consequences of birth timing relative to other females and the prevalence of birth synchrony in cooperatively breeding Kalahari meerkats (Suricata suricatta). We show that, although there would be substantial benefits to females in synchronizing births and reducing their risk of infanticide, birth synchrony is rare. Since precise breeding synchrony has evolved in a related species with similar infanticidal female reproductive conflict, its absence in meerkats requires an evolutionary explanation. We therefore explore the costs and benefits of synchronizing breeding in two theoretical models, each of which contrasts synchrony with an alternative reproductive strategy: (i) breeding opportunistically and accepting fitness losses to infanticide or (ii) suppressing the reproduction of others to prevent infanticide. Our models show that the costs of synchrony constrain its development if subordinates breed infrequently, and that selection instead favours the suppression of subordinate reproduction by the dominant and opportunistic reproduction by subordinates. Together, our results suggest that the resolution of reproductive conflict in animal societies is shaped by differential breeding propensities among female group members, leading to divergent conflict resolution strategies even in closely-related species.

在由多个共同繁殖雌性组成的动物社群中，雌性杀婴行为（female infanticide）极为普遍。为规避自身后代被杀害的风险，雌性个体可通过同步繁殖并集中抚育幼崽的策略，使其他雌性难以分辨并误杀自身子代。然而，雌性繁殖冲突并非必然导致繁殖同步性，目前学界仍缺乏可解释不同物种间冲突解决策略差异的通用假说。本研究以合作繁殖的喀拉狐獴（Suricata suricatta）为对象，探究了相对于群体内其他雌性的产仔时机对个体适合度的影响，以及产仔同步性的发生频率。研究结果显示，尽管雌性个体通过同步产仔以降低杀婴风险可获得显著收益，但产仔同步性实则十分罕见。鉴于亲缘关系相近且存在类似雌性杀婴繁殖冲突的物种已演化出精准的繁殖同步性，狐獴种群中繁殖同步性的缺失需要进化层面的合理解释。为此，我们构建了两类理论模型，分别将同步繁殖策略与两种替代繁殖策略进行对比：（i）采取机会主义式繁殖，并承担因杀婴导致的适合度损失；（ii）抑制其他个体的繁殖活动以避免自身后代遭遇杀婴。模型结果表明，当下级雌性繁殖频率较低时，同步繁殖的成本会制约其演化，此时自然选择更倾向于优势个体抑制下级的繁殖行为，同时下级个体采取机会主义式繁殖。综合来看，本研究结果表明，动物社群中的繁殖冲突解决机制，取决于雌性社群成员间差异化的繁殖倾向，即使是亲缘关系相近的物种，也可能演化出截然不同的冲突解决策略。