Data from: No geographic variation in thermoregulatory color plasticity and limited variation in heat-avoidance behavior in Battus philenor caterpillars

Phenotypic plasticity can help organisms cope with variation in their current environment, including temperature variation, but not all environments are equally variable. In the least variable or extreme environments, plasticity may no longer be used. In this case, the plasticity could be lost all together, or it could persist with either the same or an altered reaction norm, depending on factors such as the plasticity's costs. In the pipevine swallowtail caterpillar (Battus philenor), I tested for changes in two forms of heat-avoidance plasticity, color change and refuge-seeking behavior, across the species’ range in the United states, including the cooler eastern parts of its range where color change has not been observed and is unlikely to be needed. I found that both heat-avoidance behavior and color change persisted in all surveyed populations. Indeed, the reaction norm for color change remained nearly unaltered, while the threshold for refuge-seeking only changed slightly across populations. These results suggest that the costs of these plastic traits are low enough for them to be maintained by whatever minimal gene flow the population receives. I show that plasticity can be maintained unaltered in populations where it is not used and discuss the potential consequences of this persistence for both the ecology and evolution of plasticity.表型可塑性（phenotypic plasticity）可帮助生物应对当前所处环境的波动（包括温度变化），但并非所有环境的变异程度都一致。在变异程度最低或极端的环境中，生物可能不再利用表型可塑性。此时，该可塑性既可能完全丢失，也可能以原有或经修饰的反应规范（reaction norm）得以存续，具体取决于可塑性的成本等因素。本研究以马兜铃凤蝶幼虫（Battus philenor）为对象，在美国境内该物种的分布范围内，针对两种避热可塑性形式——体色变化与避难搜寻行为——开展了变化趋势检测，其中涵盖了其分布区内较为凉爽的东部区域——此前未在该区域观测到体色变化现象，且该性状也不太可能被利用。研究结果显示，所有被调查种群均保留了避热行为与体色变化两种可塑性。具体而言，体色变化的反应规范几乎未发生改变，而避难搜寻行为的阈值仅在不同种群间出现轻微变化。上述结果表明，这两种可塑性性状的成本足够低，足以通过种群接收的微弱基因流得以维持。本研究证实，即便在不使用表型可塑性的种群中，该性状仍可保持不变并得以存续，并探讨了这种可塑性保留现象对表型可塑性生态学与进化研究的潜在影响。