Data from: Negative association between parental care and sibling cooperation in earwigs: a new perspective on the early evolution of family life?

The evolution of family life requires net fitness benefits for offspring, which are commonly assumed to mainly derive from parental care. However, an additional source of benefits for offspring is often overlooked: cooperative interactions among juvenile siblings. In this study, we examined how sibling cooperation and parental care could jointly contribute to the early evolution of family life. Specifically, we tested whether the level of food transferred among siblings (sibling cooperation) in the European earwig Forficula auricularia (1) depends on the level of maternal food provisioning (parental care), and (2) is translated into offspring survival, as well as female investment into future reproduction. We show that higher levels of sibling food transfer were associated with lower levels of maternal food provisioning, possibly reflecting a compensatory relationship between sibling cooperation and maternal care. Furthermore, the level of sibling food transfer did not influence offspring survival, but was associated with negative effects on the production of the second and terminal clutch by the tending mothers. These findings indicate that sibling cooperation could mitigate the detrimental effects on offspring survival that result from being tended by low quality mothers. More generally, they are in line with the hypothesis that sibling cooperation is an ancestral behavior that can be retained to compensate for insufficient levels of parental investment.

家庭生活的演化需要为后代带来净适合度收益，这类收益通常被认为主要源自亲代照料。然而，后代可获得的另一项收益来源往往遭到忽视：幼龄同胞间的合作互动。本研究探讨了同胞合作与亲代照料如何共同推动家庭生活的早期演化。具体而言，我们针对欧洲球螋（Forficula auricularia）开展了两项检验：其一，同胞间的食物传递水平（即同胞合作）是否随母体食物投喂量（即亲代照料水平）发生变化；其二，该食物传递水平是否会影响后代存活率，以及抚育母体对未来繁殖的投入。
研究结果表明，同胞间食物传递水平越高，母体的食物投喂量则越低，这或许反映了同胞合作与母体照料之间存在补偿关系。此外，同胞间的食物传递水平并未对后代存活率产生显著影响，但与抚育母体产生第二窝（亦是终末窝）卵块的繁殖产量呈负相关。上述发现提示，同胞合作能够缓解因照料子代的母体质量欠佳而对后代存活率造成的不利影响。更具普遍意义而言，这些结果与“同胞合作是一种祖先行为，可用于弥补亲代投入不足”的假说相契合。