Instituto de Ciencias Ambientales y Evolutivas, Universidad Austral de Chile, Valdivia, Chile.
PLoS One. 2013 Aug 5;8(8):e70662. doi: 10.1371/journal.pone.0070662. Print 2013.
The ability of organisms to perform at different temperatures could be described by a continuous nonlinear reaction norm (i.e., thermal performance curve, TPC), in which the phenotypic trait value varies as a function of temperature. Almost any shift in the parameters of this performance curve could highlight the direct effect of temperature on organism fitness, providing a powerful framework for testing thermal adaptation hypotheses. Inter-and intraspecific differences in this performance curve are also reflected in thermal tolerances limits (e.g., critical and lethal limits), influencing the biogeographic patterns of species' distribution. Within this context, here we investigated the intraspecific variation in thermal sensitivities and thermal tolerances in three populations of the invasive snail Cornu aspersum across a geographical gradient, characterized by different climatic conditions. Thus, we examined population differentiation in the TPCs, thermal-coma recovery times, expression of heat-shock proteins and standard metabolic rate (i.e., energetic costs of physiological differentiation). We tested two competing hypotheses regarding thermal adaptation (the "hotter is better" and the generalist-specialist trade-offs). Our results show that the differences in thermal sensitivity among populations of C. aspersum follow a latitudinal pattern, which is likely the result of a combination of thermodynamic constraints ("hotter is better") and thermal adaptations to their local environments (generalist-specialist trade-offs). This finding is also consistent with some thermal tolerance indices such as the Heat-Shock Protein Response and the recovery time from chill-coma. However, mixed responses in the evaluated traits suggest that thermal adaptation in this species is not complete, as we were not able to detect any differences in neither energetic costs of physiological differentiation among populations, nor in the heat-coma recovery.
生物体在不同温度下的表现能力可以用连续的非线性反应规范（即热性能曲线，TPC）来描述，其中表型特征值随温度而变化。这条性能曲线的任何参数变化都可能突出温度对生物体适应性的直接影响，为测试热适应假说提供了一个强有力的框架。这种性能曲线的种间和种内差异也反映在热容忍极限（例如，临界和致死极限）中，影响着物种分布的生物地理模式。在这种情况下，我们研究了三种入侵蜗牛 Cornu aspersum 在地理梯度上的热敏感性和热容忍性的种内变异，这些地理梯度的气候条件不同。因此，我们检查了 TPC、热昏迷恢复时间、热休克蛋白表达和标准代谢率（即生理分化的能量成本）方面的种群分化。我们检验了两个关于热适应的竞争假说（“更热更好”和特化-广化权衡）。我们的结果表明，C. aspersum 种群之间的热敏感性差异遵循纬度模式，这可能是热力学限制（“更热更好”）和对当地环境的热适应（特化-广化权衡）的综合结果。这一发现也与某些热耐受指数（如热休克蛋白反应和冷昏迷恢复时间）一致。然而，评估特征的混合反应表明，该物种的热适应性并不完全，因为我们在种群间的生理分化的能量成本方面，以及在热昏迷恢复方面，都没有检测到任何差异。
