Data from: Body size, swimming speed, or thermal sensitivity? Predator-imposed selection on amphibian larvae

Background: Many animals rely on their escape performance during predator encounters. Because of its dependence on body size and temperature, escape velocity is fully characterized by three measures, absolute value, size-corrected value, and its response to temperature (thermal sensitivity). The primary target of the selection imposed by predators is poorly understood. We examined predator (dragonfly larva)-imposed selection on prey (newt larvae) body size and characteristics of escape velocity using replicated and controlled predation experiments under seminatural conditions. Specifically, because these species experience a wide range of temperatures throughout their larval phases, we predict that larvae achieving high swimming velocities across temperatures will have a selective advantage over more thermally sensitive individuals. Results: Nonzero selection differentials indicated that predators selected for prey body size and both absolute and size-corrected maximum swimming velocity. Comparison of selection differentials with control confirmed selection only on body size, i.e., dragonfly larvae preferably preyed on small newt larvae. Maximum swimming velocity and its thermal sensitivity showed low group repeatability, which contributed to non-detectable selection on both characteristics of escape performance. Conclusions: In the newt-dragonfly larvae interaction, body size plays a more important role than maximum values and thermal sensitivity of swimming velocity during predator escape. This corroborates the general importance of body size in predator–prey interactions. The absence of an appropriate control in predation experiments may lead to potentially misleading conclusions about the primary target of predator-imposed selection. Insights from predation experiments contribute to our understanding of the link between performance and fitness, and further improve mechanistic models of predator–prey interactions and food web dynamics.研究背景：诸多动物在遭遇捕食者时需依赖逃逸性能。逃逸速度受体型与温度共同调控，可通过三项指标完整表征：绝对逃逸速度、体型校正后的逃逸速度，以及其对温度的响应（热敏感性）。当前学界对捕食者施加的选择压力的主要作用靶标仍不甚明晰。本研究在半自然条件下开展重复可控的捕食实验，以探究捕食者（蜻蜓幼虫）对猎物（蝾螈幼虫）的体型及逃逸速度特性所施加的选择压力。鉴于该物种的幼虫阶段会经历广泛的温度波动，我们推测：在不同温度下均能维持较高游泳速度的幼虫，相较于热敏感性更强的个体，将获得更高的选择优势。研究结果：非零的选择差异值表明，捕食者对猎物的体型、绝对最大游泳速度及体型校正后的最大游泳速度均存在选择偏好。通过将选择差异值与对照组进行比对，我们确认捕食者仅对猎物体型存在显著选择——即蜻蜓幼虫更偏好捕食体型较小的蝾螈幼虫。最大游泳速度及其热敏感性的组内重复度较低，这使得我们未能检测到针对这两项逃逸性能指标的选择压力。研究结论：在蝾螈幼虫与蜻蜓幼虫的捕食互动中，相较于最大游泳速度及其热敏感性，体型在捕食逃逸过程中扮演着更为关键的角色。这一发现进一步证实了体型在捕食者-猎物互作中的普遍重要性。若捕食实验中未设置恰当的对照组，可能会得出关于捕食者选择压力主要靶标的误导性结论。本研究从捕食实验中获得的认识，有助于深化我们对性能与适合度之间关联的理解，并进一步优化捕食者-猎物互作及食物网动态的机制模型。