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进化限制的两大主流假说——越热越好预期（hotter-is-better expectation）与特化-泛化权衡（specialist–generalist trade-off）——在检验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果，是否源于对这些限制应发挥作用的组织层级（即物种>种群>个体）的认知混淆？我们提出，由于两类假说的底层成因与作用要求存在差异，这些进化限制应在不同的组织层级得以体现。越热越好预期仅应在独立进化单元（如物种、种群）之间体现，而无法在种群内部观测到。相较之下，特化-泛化权衡既可在独立进化单元之间体现，也可在种群内部观测到。我们针对代表10个种群的440只雨林日照石龙子（Lampropholis coggeri）测量了其短跑性能的热敏感性，并利用所得的性能曲线，在两个组织层级下检验上述假说限制的存在证据：(i) 种群间；(ii) 种群内。结果与预期一致，越热越好预期仅在种群间层级得到验证，而特化-泛化权衡则同时在种群内部与种群间层级得到验证。我们的研究结果表明，根据驱动进化限制的具体过程不同，其可在不同的组织层级得以体现。若能考虑这些潜在驱动过程，以及某一限制应发挥作用的组织层级，或有助于解决实证研究中相互矛盾的结果。