Evolutionary Stress Ecology and Ecotoxicology, University of Leuven, Leuven, Belgium.
J Anim Ecol. 2019 Dec;88(12):1961-1972. doi: 10.1111/1365-2656.13088. Epub 2019 Sep 6.
Trait-based studies are needed to understand the plastic and genetic responses of organisms to warming. A neglected organismal trait is elemental composition, despite its potential to cascade into effects on the ecosystem level. Warming is predicted to shape elemental composition through shifts in storage molecules associated with responses in growth, body size and metabolic rate. Our goals were to quantify thermal response patterns in body composition and to obtain insights into their underlying drivers and their evolution across latitudes. We reconstructed the thermal response curves (TRCs) for body elemental composition [C (carbon), N (nitrogen) and the C:N ratio] of damselfly larvae from high- and low-latitude populations. Additionally, we quantified the TRCs for survival, growth and development rates and body size to assess local thermal adaptation, as well as the TRCs for metabolic rate and key macromolecules (proteins, fat, sugars and cuticular melanin and chitin) as these may underlie the elemental TRCs. All larvae died at 36°C. Up to 32°C, low-latitude larvae increased growth and development rates and did not suffer increased mortality. Instead, growth and development rates of high-latitude larvae were lower and levelled off at 24°C, and mortality increased at 32°C. This latitude-associated thermal adaptation pattern matched the 'hotter-is-better' hypothesis. With increasing temperatures, low-latitude larvae decreased C:N, while high-latitude larvae increased C:N. These patterns were driven by associated changes in N contents, while C contents did not respond to temperature. Consistent with the temperature-size rule and the thermal melanism hypothesis, body size and melanin levels decreased with warming. While all traits and associated macromolecules (except for metabolic rate that showed thermal compensation) assumed to underlie thermal responses in elemental composition showed thermal plasticity, these were largely independent and none could explain the stoichiometric TRCs. Our results highlight that thermal responses in elemental composition cannot be explained by traditionally assumed drivers, asking for a broader perspective including the thermal dependence of elemental fluxes. Another key implication is that thermal evolution can reverse the plastic stoichiometric thermal responses and hence reverse how warming may shape food web dynamics through changes in body composition at different latitudes.
为了了解生物体对变暖的可塑性和遗传响应，需要进行基于特征的研究。尽管元素组成有可能在生态系统层面产生级联效应，但它是一个被忽视的生物体特征。变暖预计会通过与生长、体型和代谢率反应相关的储存分子的变化来塑造元素组成。我们的目标是量化身体成分的热响应模式，并深入了解其潜在的驱动因素及其在纬度上的演变。我们重建了来自高纬度和低纬度种群的蜻蜓幼虫身体元素组成[C（碳）、N（氮）和 C:N 比]的热响应曲线（TRC）。此外，我们量化了生存、生长和发育速度以及体型的 TRC，以评估局部热适应，以及代谢率和关键大分子（蛋白质、脂肪、糖和角质黑色素和几丁质）的 TRC，因为它们可能是元素 TRC 的基础。所有幼虫在 36°C 时死亡。在 32°C 以下，低纬度幼虫增加了生长和发育速度，并且没有增加死亡率。相反，高纬度幼虫的生长和发育速度较低，并在 24°C 时趋于平稳，而 32°C 时死亡率增加。这种与纬度相关的热适应模式与“越热越好”假说相匹配。随着温度的升高，低纬度幼虫的 C:N 降低，而高纬度幼虫的 C:N 增加。这些模式是由 N 含量的相关变化驱动的，而 C 含量对温度没有反应。与温度-体型法则和热黑化假说一致，随着温度的升高，体型和黑色素水平下降。虽然所有的特征和相关的大分子（除了代谢率表现出热补偿）都被认为是元素组成热反应的基础，但这些特征大多是独立的，没有一个可以解释化学计量学 TRC。我们的结果强调，元素组成的热反应不能用传统的假设驱动因素来解释，需要更广泛的视角，包括元素通量的热依赖性。另一个关键的启示是，热进化可以逆转可塑的化学计量学热反应，从而通过在不同纬度上改变身体组成来改变食物网动态。
