Data from: Can newts cope with the heat? Disparate thermoregulatory strategies of two sympatric species in water

Many ectotherms effectively reduce their exposure to low or high environmental temperatures using behavioral thermoregulation. In terrestrial ectotherms, thermoregulatory strategies range from accurate thermoregulation to thermoconformity according to the costs and limits of thermoregulation, while in aquatic taxa the quantification of behavioral thermoregulation have received limited attention. We examined thermoregulation in two sympatric newt species, Ichthyosaura alpestris and Lissotriton vulgaris, exposed to elevated water temperatures under semi-natural conditions. According to a recent theory, we predicted that species for which elevated water temperatures pose a lower thermal quality habitat, would thermoregulate more effectively than species in thermally benign conditions. In the laboratory thermal gradient, L. vulgaris maintained higher body temperatures than I. alpestris. Semi-natural thermal conditions provided better thermal quality of habitat for L. vulgaris than for I. alpestris. Thermoregulatory indices indicated that I. alpestris actively thermoregulated its body temperature, whereas L. vulgaris remained passive to the thermal heterogeneity of aquatic environment. In the face of elevated water temperatures, sympatric newt species employed disparate thermoregulatory strategies according to the species-specific quality of the thermal habitat. Both strategies reduced newt exposure to suboptimal water temperatures with the same accuracy but with or without the costs of thermoregulation. The quantification of behavioral thermoregulation proves to be an important conceptual and methodological tool for thermal ecology studies not only in terrestrial but also in aquatic ectotherms.诸多变温动物（ectotherm）可借助行为体温调节（behavioral thermoregulation），有效降低自身暴露于极端低温或高温环境的风险。对于陆生变温动物，其体温调节策略会依据体温调节的成本与限制条件，在精准体温调节至体温顺应（thermoconformity）之间动态调整；但目前学界对水生类群（aquatic taxa）行为体温调节的量化研究仍较为薄弱。本研究选取两种同域分布的蝾螈——阿尔卑斯蝾螈（Ichthyosaura alpestris）与普通欧螈（Lissotriton vulgaris），在半自然条件（semi-natural conditions）下探究其在水温升高环境中的体温调节行为。基于近期提出的热生态学理论，我们提出如下假说：当水温升高导致栖息地热质量下降时，相较于栖息于热环境适宜区域的物种，此类物种会采取更为高效的体温调节策略。在实验室温度梯度（thermal gradient）实验中，普通欧螈维持的体温高于阿尔卑斯蝾螈。半自然热环境下，普通欧螈的栖息地热质量显著优于阿尔卑斯蝾螈。体温调节指数分析显示，阿尔卑斯蝾螈会主动调控自身体温，而普通欧螈则对水生环境的热异质性（thermal heterogeneity）呈现被动适应状态。面对水温升高的胁迫环境，同域分布的两种蝾螈会依据各自物种特异性的热栖息地（thermal habitat）质量，采取截然不同的体温调节策略。两种策略均以相同精度降低了蝾螈暴露于次优水温（suboptimal water temperatures）的概率，其中一种策略需付出体温调节的代谢成本，而另一种则无需此类成本。行为体温调节的量化研究，不仅是陆生变温动物热生态学（thermal ecology）研究的重要概念与方法工具，对水生变温动物的相关研究而言同样具有关键意义。