Data from: Do evolutionary constraints on thermal performance manifest at different organizational scales?

The two foremost hypotheses on the evolutionary constraints on an organism's thermal sensitivity – the hotter-is-better expectation, and the specialist–generalist trade-off – have received mixed support from empirical studies testing for their existence. Could these conflicting results reflect confusion regarding the organizational level (i.e. species > population > individual) at which these constraints should manifest? We propose that these evolutionary constraints should manifest at different organizational levels because of differences in their underlying causes and requirements. The hotter-is-better expectation should only manifest across separate evolutionary units (e.g. species, populations), and not within populations. The specialist–generalist trade-off, by contrast, should manifest within as well as between separate evolutionary units. We measured the thermal sensitivity of sprint performance for 440 rainforest sun skinks (Lampropholis coggeri) representing 10 populations, and used the resulting performance curves to test for evidence for the hypothesized constraints at two organizational levels: (i) across populations and (ii) within populations. As predicted, the hotter-is-better expectation was evident only at the across-population level, whereas the specialist–generalist trade-off was evident within, as well as across, populations. Our results suggest that, depending on the processes that drive them, evolutionary constraints can manifest at different organizational levels. Consideration of these underlying processes, and the organizational level at which a constraint should manifest, may help resolve conflicting empirical results.关于生物体热敏感性的进化约束，目前存在两大主流假说——“越热越好”假说（hotter-is-better expectation）与特化者-泛化者权衡（specialist–generalist trade-off）——相关实证研究对其存在性的支持证据存在分歧。这类相悖的研究结果，是否源于对该类进化约束应显现的组织层级（即物种>种群>个体）存在认知混淆？我们提出，鉴于两类假说的底层成因与作用需求存在差异，其对应的进化约束应在不同的组织层级显现：“越热越好”假说仅应在独立进化单元（evolutionary units，如物种、种群）间显现，而非局限于种群内部；而特化者-泛化者权衡则应同时在种群内部以及独立进化单元间显现。我们针对代表10个自然种群的440只雨林太阳石龙子（Lampropholis coggeri）的疾跑性能（sprint performance）热敏感性开展了测定，并通过所得的性能曲线，在两个组织层级检验对应假说约束的存在证据：(i) 种群间层级；(ii) 种群内部层级。实验结果与预期一致：“越热越好”假说仅在种群间层级得到验证，而特化者-泛化者权衡则同时在种群内部与种群间均得到支持。本研究结果表明，进化约束可依据其驱动过程的差异，在不同的组织层级显现。若能兼顾这类底层驱动过程，以及某一约束效应应显现的组织层级，或可有效解决相关实证研究中的相悖结论。