Thermal physiology responds to interannual temperature shifts in a montane horned lizard, Phrynosoma orbiculare

As climate change marches on, rapidly rising temperatures shatter records every year, presenting ever‐growing physiological challenges to organisms worldwide. Ectotherms rely on behavioral and physiological plasticity to contend with environmental fluctuations. Nonetheless, our understanding of thermal plasticity has been largely limited to laboratory settings. Here, we test whether aspects of thermal physiology respond to interannual shifts in thermal environment in a natural population of Phrynosoma orbiculare, a montane horned lizard, from Hidalgo, Mexico. At our field site, 2019 was markedly warmer than the year that preceded it. We detected population‐level increases in three key thermal physiological traits: preferred temperature, the critical thermal minimum, and the critical thermal maximum. Thus, thermal phenotypes appear to shift in tandem in response to environmental fluctuations. A subset of individuals were resampled across years, allowing insight into plastic shifts within an organism's lifetime. We detected parallel increases in these lizards for the preferred temperature and the critical thermal minimum, but not for the critical thermal maximum. Our results support a growing body of literature indicating that preferred conditions and cold tolerance can be highly labile over the course of an organism's lifetime, whereas hardening over shorter time periods is more common for heat tolerance. Given that heat tolerance increased at the population‐level, but not in resampled individuals, it is possible that rapid evolution occurred due to temperature increases. In short, physiological shifts can be observed in natural populations over relatively short timespans, and these shifts might reflect a combination of evolutionary and acclimatory responses.

随着气候变化持续演进，全球气温逐年攀升并屡创纪录，给全球各类生物带来了愈发严峻的生理挑战。变温动物（ectotherms）依赖行为与生理可塑性来应对环境波动。然而，当前学界对热可塑性（thermal plasticity）的认知大多局限于实验室环境。本研究针对来自墨西哥伊达尔戈州的山地角蜥（Phrynosoma orbiculare）这一山地蜥蜴自然种群，探究其热生理特征是否会响应热环境的年际变化。在本研究的野外样地中，2019年的气温显著高于前一年。研究团队检测到三项关键热生理性状出现种群水平的显著提升：偏好体温（preferred temperature）、临界低温下限（critical thermal minimum）与临界高温上限（critical thermal maximum）。由此可见，热表型（thermal phenotypes）似乎会随环境波动同步发生适应性改变。我们对部分个体进行了跨年度重采样，得以解析生物个体生命周期内的可塑性变化。研究发现，这些蜥蜴的偏好体温与临界低温下限同样出现提升，但临界高温上限未检测到显著变化。本研究结果支持了日益增长的相关研究共识：生物个体生命周期内，其偏好环境条件与耐寒性可发生高度易变的可塑性变化；而短时热耐受硬化（thermal hardening）现象在热耐受性状中更为常见。鉴于种群水平的热耐受能力出现提升，但重采样个体未呈现该变化，我们推测温度升高可能触发了快速进化过程。简言之，自然种群可在相对较短的时间跨度内发生生理改变，这类改变可能同时反映了进化响应与驯化响应（acclimatory response）的共同作用。