Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology (NTNU), Høgskoleringen 5, Realfagbygget, 7491, Trondheim, Norway.
Department of Biology, Norwegian University of Science and Technology (NTNU), Høgskoleringen 5, Realfagbygget, 7491, Trondheim, Norway.
Sci Rep. 2021 Dec 8;11(1):23594. doi: 10.1038/s41598-021-03051-y.
In ectotherms, adult body size commonly declines with increasing environmental temperature, a pattern known as the temperature-size rule. One influential hypothesis explaining this observation is that the challenge of obtaining sufficient oxygen to support metabolism becomes greater with increasing body size, and more so at high temperatures. Yet, previous models based on this hypothesis do not account for phenotypic plasticity in the physiology of organisms that counteracts oxygen limitation at high temperature. Here, we model the predicted strength of the temperature-size response using estimates of how both the oxygen supply and demand is affected by temperature when allowing for phenotypic plasticity in the aquatic ectotherm Daphnia magna. Our predictions remain highly inconsistent with empirical temperature-size responses, with the prior being close to one order of magnitude stronger than the latter. These results fail to provide quantitative support for the hypothesis that oxygen limitation drives temperature-size clines in aquatic ectotherms. Future studies into the role of oxygen limitation should address how the strength of the temperature-size response may be shaped by evolution under fluctuating temperature regimes. Finally, our results caution against applying deterministic models based on the oxygen limitation hypothesis when predicting future changes in ectotherm size distributions under climate change.
在变温动物中，成年体型通常随着环境温度的升高而减小，这种模式被称为温度-体型规律。一个有影响力的假说解释了这一观察结果，即随着体型的增大，获得足够氧气来支持新陈代谢的挑战变得更大，而在高温下则更为严重。然而，基于这一假说的先前模型并没有考虑到生物体在高温下对氧气限制的生理表型可塑性。在这里，我们使用估计的方法来模拟预测温度-体型反应的强度，这些估计方法考虑了在允许水生变温动物大型溞的表型可塑性的情况下，温度对氧气供应和需求的影响。我们的预测与经验性的温度-体型反应仍然高度不一致，前者比后者强近一个数量级。这些结果未能为氧气限制驱动水生变温动物的温度-体型梯度的假说提供定量支持。未来关于氧气限制作用的研究应该解决在波动的温度条件下，进化如何塑造温度-体型反应的强度。最后，我们的结果告诫人们，在预测气候变化下变温动物体型分布的未来变化时，应避免使用基于氧气限制假说的确定性模型。
