Data from: Choosy cannibals preferentially consume siblings with relatively low fitness prospects

When an individual can selfishly cannibalize a relative or altruistically set it free, the benefits of altruism will be positively associated with the relative's fitness prospects (the benefits it receives from altruism). We tested the prediction that altruism should be preferentially directed toward high-quality relatives using larvae of the New Mexican spadefoot toad (Spea multiplicata), a species in which tadpoles plastically express omnivore and carnivore ecomorphs. In a no-choice design, we presented carnivores with sibling or nonsibling omnivores varying in developmental stage, which is positively associated with survival in this toad's ephemeral larval environment. There was a significant interaction between relatedness and developmental stage on the probability of cannibalism: carnivores were overall more likely to cannibalize less developed omnivores, but this effect was exaggerated when the potential victim was a sibling. This evidence that altruists favor relatives with high fitness prospects highlights the numerous factors shaping altruism's payoffs.

当个体可选择自私地同类相食亲属，或是利他地释放该亲属时，利他行为的收益将与该亲属的适合度前景（fitness prospects，即该亲属从利他行为中获得的收益）呈正相关。我们以新墨西哥锄足蟾（Spea multiplicata）的幼体为实验材料，检验了“利他行为应优先指向高质量亲属”这一预测。该物种的蝌蚪可通过表型可塑性分化为杂食型与肉食型生态型（ecomorphs）。在无选择实验设计（no-choice design）中，我们向肉食型蝌蚪提供发育阶段各异的同胞（sibling）或非同胞（nonsibling）杂食型蝌蚪；在该锄足蟾的临时性幼虫生境中，发育阶段与存活率呈显著正相关。同类相食概率存在亲缘关系（relatedness）与发育阶段的显著交互效应：整体而言，肉食型蝌蚪更倾向于捕食发育程度较低的杂食型蝌蚪，且当潜在猎物为同胞时，这一效应会被显著放大。这项表明利他者倾向于偏好高适合度前景亲属的实验证据，凸显了调控利他行为收益的诸多关键因素。