Data from: Social role specialization promotes cooperation between parents

Biparental care of offspring is a widespread social behavior, and various ecological, life-history and demographic factors have been proposed to explain its evolution and maintenance. Raising offspring generally requires several types of care (e.g. feeding, brooding, defense), and males and females often specialize in providing different types of care. However, theoretical models of care often assume that 'care' is a single variable, and hence that a unit of care by the mother is interchangeable with a unit of care by the father. We hypothesize that the ability of one parent to provide all types of care may be limited by non-additive costs, or by sex-based asymmetries in the costs of particular care types. Using an individual-based simulation, we show that synergistic costs of investing in two tasks, or a negligible sex-based cost asymmetry, select for task specialization and biparental care. Biparental care persists despite intense sexual selection and sex-biased mortality, suggesting that previous models make overly restrictive predictions of the conditions under which cooperation can be maintained. Our model provides a mechanistic underpinning for published models that show synergistic benefits of individuals cooperating can stabilize cooperation, both in the context of parental care and in other social scenarios.双亲抚育（Biparental care）后代是一种广泛分布的社会行为，学界已提出多种生态、生活史及人口统计学因素，用以解释其演化与维持过程。抚育后代通常需要多类照料行为（如觅食、育雏、防御等），雄性与雌性往往会在不同照料类型上形成专业化分工。然而，现有抚育行为的理论模型往往将“照料”假设为单一变量，因此认为雌性提供的一单位照料与雄性提供的一单位照料可完全互换。我们提出假说：某一亲本能否提供全部类型的照料，可能受限于非加性成本，或是特定照料类型的成本存在性别不对称性。通过基于个体的模拟（individual-based simulation），我们发现，当个体同时投资两项任务会产生协同成本，或是性别间的成本不对称性可忽略时，会演化出任务专业化分工与双亲抚育行为。即便面临强烈的性选择与性别偏向性死亡率，双亲抚育行为仍可维持，这表明此前的模型对合作得以维持的条件做出了过于严苛的预测。本模型为已发表的相关理论模型提供了机制层面的支撑——这些模型曾证实，个体间合作带来的协同收益能够稳定合作行为，这一结论不仅适用于亲本抚育场景，也可推广至其他社会互动情境中。