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，或是利他地将其释放时，利他行为的收益将与该亲属的适合度前景（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）的幼体为实验对象，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表达杂食性与肉食性两种生态型。在无选择实验设计中，我们为肉食性蝌蚪提供了发育阶段各异的同胞或非同胞杂食性蝌蚪；在该蟾蜍的临时幼体生境中，发育阶段与存活率呈正相关。同类相食概率与亲缘关系和发育阶段之间存在显著交互作用：总体而言，肉食性蝌蚪更倾向于捕食发育程度较低的杂食性蝌蚪，且当潜在猎物为同胞时，这一效应会被放大。这项证实利他者更青睐高适合度前景亲属的研究结果，凸显了诸多塑造利他行为收益的因素。