Data from: The consequences of lifetime and evolutionary exposure to toxic prey: changes in avoidance behavior through ontogeny

Responses to novel threats (e.g. invasive species) can involve genetic changes or plastic shifts in phenotype. There is controversy over the relative importance of these processes for species survival of such perturbations, but we are realizing they are not mutually exclusive. Native eastern fence lizards (Sceloporus undulatus) have adapted to top-down predation pressure imposed by the invasive red imported fire ant (Solenopsis invicta) via changes in adult (but not juvenile) lizard antipredator behavior. Here we examine the largely ignored, but potentially equally important, bottom-up effect of fire ants as toxic prey for lizards. We test how fire ant consumption (or avoidance) is affected by lifetime (via plasticity) and evolutionary (via natural selection) exposure to fire ants by comparing field-caught and lab-reared lizards, respectively, from fire ant invaded and uninvaded populations. More naive juveniles from invaded populations ate fire ants than did adults, reflecting a natural ontogenetic dietary shift away from ants. Lab-reared lizards from the invaded site were less likely to eat fire ants than were those from the uninvaded site, suggesting a potential evolutionary shift in feeding behavior. Lifetime and evolutionary exposure interacted across ontogeny, however, and field-caught lizards from the invaded site exhibited opposite ontogenetic trends; adults were more likely to eat fire ants than were juveniles. Our results suggest that plastic and evolutionary processes may both play important roles in permitting species survival of novel threats. We further reveal how complex interactions can shape adaptive responses to multi-modal impacts imposed by invaders: in our system fire ants impose stronger bottom-up selection than top-down selection, with each selection regime changing differently across lizard ontogeny.

针对入侵物种等新型威胁，生物体可通过遗传改变或表型可塑性变化实现应对。目前学界对于这两类过程在物种抵御此类扰动的生存中相对重要性尚存争议，但现已明确二者并非互斥。本土东部栅栏蜥蜴（*Sceloporus undulatus*）已通过成体（而非幼体）的反捕食行为调整，适应了入侵性红火蚁（*Solenopsis invicta*）施加的自上而下捕食压力。本研究聚焦此前长期被忽视，但潜在重要性相当的自下而上效应：即红火蚁作为蜥蜴有毒猎物所产生的影响。我们通过分别比较红火蚁入侵区与未入侵区野外捕获及实验室繁育的蜥蜴，探究终身暴露（通过表型可塑性）与进化暴露（通过自然选择）如何影响蜥蜴对红火蚁的取食（或回避）行为。来自入侵种群的幼体取食红火蚁的比例高于成体，这反映出蜥蜴随个体发育产生的天然食性转变——即逐渐远离蚁类食物。来自入侵位点的实验室繁育蜥蜴，相比未入侵位点的个体更回避取食红火蚁，这暗示取食行为可能已发生进化转变。然而，终身暴露与进化暴露在个体发育过程中存在交互作用，来自入侵位点的野外捕获蜥蜴则呈现出相反的个体发育趋势：其成体取食红火蚁的比例高于幼体。本研究结果表明，表型可塑性与进化过程均可能在物种抵御新型威胁的生存过程中发挥重要作用。我们还进一步揭示了复杂的交互作用如何塑造物种对入侵者施加的多模态影响的适应性响应：在本研究体系中，红火蚁施加的自下而上选择压力强于自上而下选择压力，且两种选择机制随蜥蜴个体发育呈现出不同的变化趋势。