Data from: The price of insurance: costs and benefits of worker production in a facultatively social bee

Kin selection theory is foundational in helping to explain the evolution of sociality; however, the degree to which indirect fitness benefits may underlie helping behavior in species of early stage sociality has received relatively little empirical attention. Facultatively social bees, which demonstrate multiple forms of social organization, provide prime systems in which to empirically test hypotheses regarding the evolutionary origins of sociality. The subsocial small carpenter bee, Ceratina calcarata, may establish a social nest by manipulating brood provisions to rear a worker daughter, which then assists in critical late-season alloparental care. Here, we combine nest demographic and behavioral data with genetic relatedness estimates to calculate the relative inclusive fitness of both subsocial and social reproductive strategies in C. calcarata. Social mothers benefit from improved likelihood of brood survivorship and have higher fitness than subsocial mothers. Worker daughters have low indirect fitness on average, and will not produce their own offspring. Among-sibling relatedness is significantly higher in social nests than subsocial nests, though mothers of either reproductive strategy may mate multiply. Though this study corroborates the ultimate role of indirect fitness and assured fitness returns in the evolution of social traits, it also offers additional support for maternal manipulation as the proximate mechanism underlying evolutionary transitions in early stage insect societies.

亲缘选择理论（Kin selection theory）是解释社会性演化的奠基性理论；然而，间接适合度收益在多大程度上支撑早期社会性类群的互助行为，相关实证研究仍相对匮乏。兼性社会性蜂类（Facultatively social bees）具备多样的社会组织形式，是实证检验社会性演化起源相关假说的理想研究体系。亚社会性小木蜂（Ceratina calcarata，subsocial small carpenter bee）可通过调控幼虫口粮培育工职雌性后代，后者会在季末关键阶段协助开展异亲抚育（alloparental care）。本研究结合巢群种群统计与行为学数据、遗传亲缘度估算结果，计算了该蜂亚社会性与社会性繁殖策略的相对广义适合度（inclusive fitness）。社会性繁殖的母蜂可获得更高的幼虫存活率，且适合度高于亚社会性母蜂。工职雌性后代的平均间接适合度较低，且无法自行产生后代。社会性巢群的同胞间亲缘度显著高于亚社会性巢群，不过两种繁殖策略的母蜂均可能存在多配行为。本研究不仅佐证了间接适合度与确定性适合度收益在社会性性状演化中的终极作用，同时为母体调控作为早期昆虫社会性演化过渡的近因机制提供了额外支持。