Data from: Fish prey change strategy with the direction of a threat

Predation is a fundamental interaction between species, yet it is unclear what escape strategies are effective for prey survival. Classical theory proposes that prey should either escape in a direction that conforms to a performance optimum or that is random and therefore unpredictable. Here, we show that larval zebrafish (Danio rerio) instead use a mixed strategy that may be either random or directed. This was determined by testing classic theory with measurements of the escape direction in response to a predator robot. We found that prey consistently escaped in a direction contralateral to the robot when approached from the side of the prey's body. At such an orientation, the predator appeared in the prey's central visual field and the contralateral response was consistent with a model of strategy that maximizes the distance from the predator. By contrast, when the robot approached the rostral or caudal ends of the body, and appeared in the prey's peripheral vision, the escape showed an equal probability of a contralateral or ipsilateral direction. At this orientation, a contralateral response offered little strategic advantage. Therefore, zebrafish larvae adopt an escape strategy that maximizes distance from the threat when strategically beneficial and that is otherwise random. This sensory-mediated mixed strategy may be employed by a diversity of animals and offers a new paradigm for understanding the factors that govern prey survival.捕食是物种间的基础互作关系，但目前仍不清楚何种逃逸策略可有效提升猎物的生存概率。经典理论提出，猎物的逃逸方向要么遵循性能最优原则，要么选择随机方向以提升不可预测性。本研究发现，斑马鱼幼体（Danio rerio）实则采用兼具随机与定向特征的混合逃逸策略。我们通过捕食者机器人诱导猎物逃逸，并测量其逃逸方向以检验经典理论，由此得出上述结论。实验结果显示，当捕食者机器人从斑马鱼幼体身体侧面发起逼近时，猎物始终朝向与机器人相对的对侧方向逃逸。此时捕食者处于斑马鱼幼体的中央视觉视野范围内，该对侧逃逸策略与最大化与捕食者间距的理论模型相符。与之相对，当机器人从幼体的吻端或尾端逼近，且捕食者处于幼体的外周视觉视野时，逃逸方向选择对侧或同侧的概率均等。此种场景下，对侧逃逸并未带来显著策略优势。综上，斑马鱼幼体的逃逸策略会在具备策略收益时最大化与威胁源的间距，其余场景则采用随机逃逸方式。这种依赖感官介导的混合逃逸策略可能广泛存在于多种动物类群中，为解析调控猎物生存的相关因素提供了全新研究范式。