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，依赖自身的逃逸表现完成避险。逃逸速度（escape velocity）因受体型与温度的双重调控，可通过三项指标完整表征：绝对数值、体型校正数值，以及其对温度的响应（热敏感性（thermal sensitivity））。目前学界对捕食者施加的选择压力的首要作用靶点仍缺乏清晰认知。为此，我们在半自然环境下开展了重复可控的捕食实验，以蜻蜓幼虫（dragonfly larva）为捕食者、蝾螈幼虫（newt larvae）为猎物，探究捕食者施加的选择压力对猎物体型及逃逸速度各项特征的影响。具体而言，鉴于这两类物种的幼虫阶段会经历宽泛的温度区间，我们推测：相较于对温度更为敏感的个体，能在多种温度下维持较高游泳速度的幼虫将获得选择优势。 研究结果：非零的选择差（selection differentials）表明，捕食者对猎物体型、绝对最大游泳速度以及体型校正后的最大游泳速度均存在选择偏好。通过将选择差与对照组进行比对，我们仅证实了针对体型的选择压力——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群体重复度较低，这导致我们无法检测到针对逃逸表现两项特征的选择压力。 研究结论：在蝾螈幼虫与蜻蜓幼虫的捕食互动中，体型在捕食逃逸过程中的作用，较游泳速度的最大值及其热敏感性更为关键。这一发现印证了体型在捕食者-猎物互作关系中的普遍重要性。若捕食实验未设置恰当的对照组，可能会得出关于捕食者施加选择压力的首要靶点的误导性结论。捕食实验所获得的研究结论，有助于我们理解运动表现与适合度之间的关联，并进一步优化捕食者-猎物互作及食物网动态的机制模型。