Collaborative Research: Experimental Tests of the Adaptive Significance of Ectotherm Thermoregulation

动物的体温对其生物学的各个方面都有深远的影响。极端的温度可能会对生理造成损害，甚至致命，但即使是中等体温也会决定生理活动和生殖输出的速率。内温动物（主要是鸟类和哺乳动物）通过调节生理机能（例如，代谢产热、排汗）来控制体温;但外温动物（例如，线虫、昆虫、鱼类、爬行动物）通常不能做到这一点。然而，外温动物可以调整它们的行为（例如，在阳光下与在阴影下花费的时间）来获得对体温的显着控制：许多人在很窄的水平上仔细调节体温（“热偏好”），这因物种而异。物种的这种热偏好通常与最大化生理性能（冲刺速度，消化效率，感官敏锐度）的温度相关，因此一个经典的假设提出，外温动物的热偏好将进化到与最大化种群增长率（“健身”）相匹配的温度。这一适应性假说被广泛接受，是生理生态学的基础，但从未被直接测试过。这一建议提供了一个严格的探索外温动物的热偏好的生物学后果。 具体而言，它开发了一套综合的实验，理论和比较研究，重点是两个物种[果蝇（果蝇），土壤线虫（线虫）]，作为经济和生态重要的动物群体（昆虫和线虫）的一般模型。该项目利用强大的新方法（由神经生物学家开发）实验操纵热偏好。这两种动物的体温调节精度将通过手术和突变来操纵，而体温偏好本身将通过人工选择（选择性育种）来改变。然后将测量由此产生的对健身的影响。如果经典的假设成立，那么（例如）个人与移位的温度调节设定点将减少健身在一个热梯度相对于他们的健身在一个固定的温度，而控制个人将显示类似的健身在两个环境中。该项目还完成了一个新的热偏好理论模型。初步模型表明，在波动的环境中的最佳设定点实际上低于在恒定的环境中的温度最大化的适应性。昆虫和蜥蜴的比较数据将被用来挑战模型的预测。这些研究具有相当大的应用相关性。建立是否以及如何热偏好实际上最大限度地提高人口增长率将有至关重要的影响，不仅为那些研究热环境对节肢动物和线虫害虫或疾病媒介的人口增长的影响，而且为应用昆虫学家需要确定具有成本效益的估计最佳温度大规模饲养的生物控制剂。

The body temperature of an animal has profound influence on all aspects of its biology. Extreme temperatures can be damaging physiologically or even lethal, but even intermediate body temperatures determine rates of physiological activities and of reproductive output. Endothermal animals (mainly birds and mammals) control their body temperatures by adjusting physiology (for example, metabolic heat production, perspiration); but ectothermal animals (e.g., nematodes, insects, fishes, reptiles) are generally unable to do this. Nevertheless, ectotherms can instead adjust their behavior (for example, amount of time spent in sun versus shade) to gain remarkable control over body temperature: many carefully regulate their body temperature at narrow levels ("thermal preferences") that vary from species to species. Such thermal preferences of species often correlate with temperatures that maximize physiological performance (sprint speed, digestive efficiency, sensory acuity), and accordingly a classical hypothesis proposes that thermal preferences of ectotherms will have evolved to match temperatures that maximize rates of population growth ("fitness"). This adaptive hypothesis is widely accepted and is fundamental to physiological ecology, but yet has never been tested directly.This proposal provides a rigorous exploration of the biological consequences of thermal preferences of ectotherms. Specifically, it develops an integrated set of experimental, theoretical, and comparative studies focusing on two species [fruitfly (Drosophila melanogaster), soil nematode (Caenorhabditis elegans)] that serve as general models for economically and ecologically important animal groups (insects and nematodes). The project exploits powerful new methods (developed by neurobiologists) of experimentally manipulating thermal preferences. Thermoregulatory precision of both animals will be manipulated both surgically and via mutation, and thermal preferences themselves will be shifted via artificial selection (selective breeding). Then the resultant impacts on fitness will be measured. If the classical hypothesis holds, then (for example) individuals with shifted thermoregulatory set-points will have reduced fitness in a thermal gradient relative to their fitness at a fixed temperature, whereas control individuals will show similar fitness in both environments. The project also completes a novel theoretical model of thermal preferences. The preliminary model shows that optimal set-points in fluctuating environments are actually lower than the temperature maximizing fitness in a constant environment. Comparative data on insects and lizards will be used to challenge the model's predictions.These studies have considerable applied relevance. Establishing whether and how thermal preferences actually maximize rates of population growth will have crucial implications not only for those studying the effects of the thermal environment on population growth of arthropod and nematode pests or disease vectors, but also for applied entomologists needing to determine cost-effective estimates of optimal temperature for mass rearing of bio-control agents.