Data from: Food-sharing vampire bats are more nepotistic under conditions of perceived risk

Cooperative behaviors exist along a spectrum of cost, from no-risk scenarios of mutual benefit to self-sacrificing altruism. Hamilton’s rule predicts that as risk increases, cooperative decisions should become increasingly kin-biased (nepotistic). To manipulate the perceived risks of regurgitated food sharing in captive vampire bats, we created a novel “rescue” condition, which required that donors leave their preferred roosting location, descend to an illuminated spot on the cage floor, and regurgitate food across cage bars to a trapped hungry bat. Vampire bats adapted their food sharing to this novel context, but with a dramatic reduction in the probability and amount of food sharing. Sixteen of 29 bats were fed by groupmates when trapped. All 15 starved bats that were tested in both trapped and free conditions received less food when trapped. Donations to trapped bats came from kin and nonkin, but subjects received a greater proportion of their food from closer relatives when trapped than when free. This finding supports the prediction that nepotistic biases should be exaggerated under dangerous conditions.

合作行为的成本存在连续谱系，从无风险的互利场景，到牺牲自我的利他行为。汉密尔顿法则（Hamilton’s rule）预测，随着风险升高，合作决策会愈发偏向亲缘关系（即裙带主义）。为操控圈养吸血蝙蝠对反哺食物共享行为的感知风险，我们设计了一种全新的“救援”实验情境：捐赠者需离开其偏好的栖息位点，下降至笼底的照明区域，并隔着笼栏向被困的饥饿蝙蝠反哺食物。吸血蝙蝠针对这一全新情境调整了食物共享行为，但食物共享的发生概率与投喂量均出现显著下降。29只被困蝙蝠中有16只获得了同伴的投喂。所有在被困与自由两种实验条件下均接受测试的15只饥饿蝙蝠，在被困状态下获得的食物量均更少。向被困蝙蝠的捐赠既来自亲缘个体也来自非亲缘个体，但相较于自由状态，受试个体在被困时从近亲处获得的食物占比更高。这一发现验证了“裙带主义偏向会在危险情境下被强化”的理论预测。