Data_Sheet_1_Individual Variation in Thermal Reaction Norms Reveals Metabolic-Behavioral Relationships in an Ectotherm.docx

Ectothermic organisms respond to rapid environmental change through a combination of behavioral and physiological adjustments. As behavioral and physiological traits are often functionally linked, an effective ectotherm response to environmental perturbation will depend on the direction and magnitude of their association. The role of various modifiers in behavioral-physiological relationships remains largely unexplored. We applied a repeated-measures approach to examine the influence of body temperature and individual variation on the link between resting metabolic rate (RMR) and exploratory locomotor activity (ELA) in juvenile Alpine newts, Ichthyosaura alpestris. We analyzed trait relationships at two body temperatures separately and as parameters, intercepts and slopes, of thermal reaction norms for both traits. Body temperature affected the level of detectable among-individual variation in two different directions. Among-individual variation in ELA was detected at 12°C, while RMR was repeatable at 22°C. We found no support for a link between RMR and ELA at either temperature. While analysis of intercepts revealed among-individual variation in both traits, among-individual variation in slopes was detected in RMR only. Intercepts were positively associated at the individual, but not the whole-phenotypic, level. For ELA, the target of selection should be individual trait values across temperatures, rather than their thermal sensitivities. The positive association between intercepts of thermal reaction norms for ELA and RMR suggests that phenotypic selection acts on both traits in a correlated fashion. Measurements at one body temperature and within-individual variation hide the metabolic-behavioral relations. We conclude that correlative studies on flexible behavioral and physiological traits in ectotherms require repeated measurement at two or more body temperatures in order to avoid misleading results. This approach is needed to fully understand ectotherm responses to environmental change and its impact on their population dynamics.

变温动物（ectothermic organisms）会通过行为调节与生理调节的协同作用，响应快速的环境变化。由于行为与生理性状通常存在功能关联，变温动物对环境扰动的有效响应，将取决于二者关联的方向与强度。目前，各类调节因子在行为-生理性状关联中的作用仍未得到充分探索。本研究采用重复测量法（repeated-measures approach），探究了体温与个体变异对幼年阿尔卑斯蝾螈（Ichthyosaura alpestris）静息代谢率（resting metabolic rate, RMR）与探索运动活性（exploratory locomotor activity, ELA）之间关联的影响。我们分别在两种体温条件下，以及针对两种性状的热反应规范（thermal reaction norms）参数——即截距与斜率——分析了性状间的关联。体温以两种不同方向影响了可检测到的个体间变异水平：在12℃时可检测到探索运动活性的个体间变异，而静息代谢率仅在22℃时具有可重复性。我们未发现两种体温条件下静息代谢率与探索运动活性存在关联的证据。尽管对截距的分析显示两种性状均存在个体间变异，但斜率的个体间变异仅在静息代谢率中被检测到。个体层面的截距呈正相关，但整体表型层面则无此关联。对于探索运动活性而言，选择作用的靶标应为不同体温下的个体性状值，而非其热敏感性。探索运动活性与静息代谢率的热反应规范截距之间的正相关，表明表型选择会以协同方式作用于这两种性状。仅在单一体温下进行的测量以及个体内变异，会掩盖代谢-行为性状间的关联。我们得出结论：针对变温动物可塑性行为与生理性状的相关性研究，需要在两种或更多体温条件下开展重复测量，以避免得出误导性结果。该方法对于全面理解变温动物对环境变化的响应及其对种群动态的影响均不可或缺。