Tropical ectotherms are particularly vulnerable to global warming because their physiologies are assumed to be adapted to narrow temperature ranges. This study explores three mechanisms potentially constraining thermal adaptation to global warming in tropical insects: (a) Trade-offs in genotypic performance at different temperatures (the jack-of-all-trades hypothesis), (b) positive genetic covariance in performance, with some genotypes performing better than others at viable temperatures (the 'winner' and 'loser' genotypes hypothesis), or (c) limited genetic variation as the potential result of relaxed selection and the loss of genes associated with responses to extreme temperatures (the gene decay hypothesis). We estimated changes in growth and survival rates at multiple temperatures for three tropical rain forest insect herbivores (Cephaloleia rolled-leaf beetles, Chrysomelidae). We reared 2,746 individuals in a full sibling experimental design, at temperatures known to be experienced by this genus of beetles in nature (i.e. 10-35°C). Significant genetic covariance was positive for 16 traits, supporting the 'winner' and 'loser' genotypes hypothesis. Only two traits displayed negative cross-temperature performance correlations. We detected a substantial contribution of genetic variance in traits associated with size and mass (0%-44%), but low heritability in plastic traits such as development time (0%-6%) or survival (0%-4%). Lowland insect populations will most likely decline if current temperatures increase between 2 and 5°C. It is concerning that local adaption is already lagging behind current temperatures. The consequences of maintaining the current global warming trajectory would be devastating for tropical insects. However, if humans can limit or slow warming, many tropical ectotherms might persist in their current locations and potentially adapt to warmer temperatures.

中文翻译：

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正遗传协方差和有限的热耐受性限制了热带昆虫对全球变暖的反应。

热带变温动物特别容易受到全球变暖的影响，因为它们的生理机能被认为适应狭窄的温度范围。本研究探讨了可能限制热带昆虫对全球变暖的热适应的三种机制：（a）不同温度下基因型性能的权衡（万事通假​​说），（b）性能的正遗传协方差，与某些基因型在可行温度下表现优于其他基因型（“赢家”和“输家”基因型假说），或 (c) 作为放松选择的潜在结果和与极端温度反应相关的基因丢失（基因衰变假设）。我们估计了三种热带雨林昆虫食草动物（Cephaloleia roll-leaf beetles、Chrysomelidae）在多种温度下的生长和存活率的变化。我们在一个完整的兄弟实验设计中饲养了 2,746 只个体，在已知的这种甲虫属在自然界中经历的温度（即 10-35°C）。16 个性状的显着遗传协方差为正，支持“赢家”和“输家”基因型假说。只有两个特征显示出负的跨温度性能相关性。我们在与大小和质量相关的性状 (0%-44%) 中检测到遗传变异的重大贡献，但在发育时间 (0%-6%) 或存活 (0%-4%) 等可塑性性状中的遗传性较低。如果当前温度升高 2 至 5°C，低地昆虫种群很可能会下降。令人担忧的是，当地的适应已经落后于当前的温度。维持当前全球变暖轨迹的后果对热带昆虫来说是毁灭性的。然而，如果人类能够限制或减缓变暖，许多热带变温动物可能会继续存在于它们目前的位置，并有可能适应更高的温度。