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限制的两大主流假说——即"温度越高表现越好"假说（hotter-is-better expectation）与"特化-泛化权衡"假说（specialist–generalist trade-off）——在验证其存在性的实证研究中得到了混杂不一的支持结果。这些相互矛盾的研究结论，是否源于对这类进化限制应显现的组织层级（即物种＞种群＞个体）存在认知混淆？我们提出，由于这两类假说的底层成因与前提要求存在差异，其对应的进化限制应在不同的组织层级显现。"温度越高表现越好"假说仅应在独立进化单元（如物种、种群）之间显现，而不应在种群内部出现。与之相对，"特化-泛化权衡"假说则应在独立进化单元内部以及单元之间均显现。我们针对代表10个种群的440只雨林太阳石龙子（*Lampropholis coggeri*）的短跑性能热敏感性开展了测量，并利用所得的性能曲线，在两个组织层级上验证假说中的进化限制是否存在：（1）种群间层级；（2）种群内部层级。正如预期，"温度越高表现越好"假说仅在种群间层级得到验证，而"特化-泛化权衡"假说则在种群内部以及种群间均获得了支持。我们的研究结果表明，进化限制可根据其驱动过程的差异，在不同的组织层级显现。若能考虑到底层驱动过程以及某一进化限制应显现的组织层级，将有助于解决实证研究中存在的矛盾结果。