University of Illinois, Champaign-Urbana, Illinois.
University of Montana, Missoula, Montana.
Mol Ecol. 2018 May;27(9):2243-2255. doi: 10.1111/mec.14580. Epub 2018 Apr 20.
Understanding the mechanisms that produce variation in thermal performance is a key component to investigating climatic effects on evolution and adaptation. However, disentangling the effects of local adaptation and phenotypic plasticity in shaping patterns of geographic variation in natural populations can prove challenging. Additionally, the physiological mechanisms that cause organismal dysfunction at extreme temperatures are still largely under debate. Using the green anole, Anolis carolinensis, we integrate measures of cold tolerance (CT ), standard metabolic rate, heart size, blood lactate concentration and RNAseq data from liver tissue to investigate geographic variation in cold tolerance and its underlying mechanisms along a latitudinal cline. We found significant effects of thermal acclimation and latitude of origin on variation in cold tolerance. Increased cold tolerance correlates with decreased rates of oxygen consumption and blood lactate concentration (a proxy for oxygen limitation), suggesting elevated performance is associated with improved oxygen economy during cold exposure. Consistent with these results, co-expression modules associated with blood lactate concentration are enriched for functions associated with blood circulation, coagulation and clotting. Expression of these modules correlates with thermal acclimation and latitude of origin. Our findings support the oxygen and capacity-limited thermal tolerance hypothesis as a potential contributor to variation in reptilian cold tolerance. Moreover, differences in gene expression suggest regulation of the blood coagulation cascade may play an important role in reptilian cold tolerance and may be the target of natural selection in populations inhabiting colder environments.
了解产生热性能变化的机制是研究气候对进化和适应影响的关键组成部分。然而，要理清本地适应和表型可塑性在塑造自然种群地理变异模式方面的作用可能具有挑战性。此外，导致生物体在极端温度下功能障碍的生理机制仍在很大程度上存在争议。我们使用绿安乐蜥（Anolis carolinensis），综合了耐冷性（CT ）、标准代谢率、心脏大小、血液乳酸浓度和来自肝脏组织的 RNAseq 数据，以调查耐冷性及其潜在机制在纬度梯度上的地理变异。我们发现热驯化和起源纬度对耐冷性的变异有显著影响。耐冷性的增加与氧消耗率和血液乳酸浓度的降低（氧限制的替代指标）相关，这表明在寒冷暴露期间，性能的提高与改善的氧气利用效率相关。与这些结果一致的是，与血液乳酸浓度相关的共表达模块与与血液循环、凝血和止血相关的功能富集。这些模块的表达与热驯化和起源纬度相关。我们的研究结果支持氧气和能力受限的热耐受假说作为爬行动物耐冷性变异的潜在贡献因素。此外，基因表达的差异表明，凝血级联的调节可能在爬行动物的耐冷性中发挥重要作用，并且可能是栖息在较冷环境中的种群中自然选择的目标。
