Prileson Eric G, Clark Jordan, Diamond Sarah E, Lenard Angie, Medina-Báez Osmary A, Yilmaz Aaron R, Martin Ryan A
Case Western Reserve University, Department of Biology, USA.
Case Western Reserve University, Department of Biology, USA.
J Therm Biol. 2023 May;114:103591. doi: 10.1016/j.jtherbio.2023.103591. Epub 2023 May 24.
Winter presents a challenge for survival, yet temperate ectotherms have remarkable physiological adaptations to cope with low-temperature conditions. Under recent climate change, rather than strictly relaxing pressure on overwintering survival, warmer winters can instead disrupt these low-temperature trait-environment associations, with negative consequences for populations. While there is increasing evidence of physiological adaptation to contemporary warming during the growing season, the effects of winter warming on physiological traits are less clear. To address this knowledge gap, we performed a common garden experiment using relatively warm-adapted versus cold-adapted populations of the acorn ant, Temnothorax curvispinosus, sampled across an urban heat island gradient, to explore the effects of winter conditions on plasticity and evolution of physiological traits. We found no evidence of evolutionary divergence in chill coma recovery nor in metabolic rate at either of two test temperatures (4 and 10 °C). Although we found the expected plastic response of increased metabolic rate under the 10 °C acute test temperature as compared with the 4 °C test temperature, this plastic response, (i.e., the acute thermal sensitivity of metabolic rate), was not different across populations. Surprisingly, we found that winter-acclimated urban ant populations exhibited higher heat tolerance compared with rural ant populations, and that the magnitude of divergence was comparable to that observed among growing-season acclimated ants. Finally, we found no evidence of differences between populations with respect to changes in colony size from the beginning to the end of the overwintering experiment. Together, these findings indicate that despite the evolution of higher heat tolerance that is often accompanied by losses in low-temperature tolerance, urban acorn ants have retained several components of low-temperature physiological performance when assessed under ecologically relevant overwintering conditions. Our study suggests the importance of measuring physiological traits under seasonally-relevant conditions to understand the causes and consequences of evolutionary responses to contemporary warming.
冬季对生物的生存构成了挑战，但温带变温动物拥有显著的生理适应性来应对低温环境。在近期的气候变化背景下，暖冬非但没有严格减轻越冬生存的压力，反而可能破坏这些低温性状与环境的关联，给种群带来负面后果。虽然越来越多的证据表明在生长季节生物对当代变暖有生理适应，但冬季变暖对生理性状的影响尚不清楚。为了填补这一知识空白，我们进行了一项共同花园实验，使用相对适应温暖环境与适应寒冷环境的橡实蚁种群（弯刺胸切叶蚁），这些种群是在城市热岛梯度上采集的，以探究冬季条件对生理性状可塑性和进化的影响。我们没有发现冷昏迷恢复以及在两个测试温度（4℃和10℃）下代谢率存在进化差异的证据。尽管我们发现与4℃测试温度相比，在10℃急性测试温度下代谢率有预期的可塑性增加反应，但这种可塑性反应（即代谢率的急性热敏感性）在不同种群间并无差异。令人惊讶的是，我们发现经过冬季适应的城市蚂蚁种群比农村蚂蚁种群表现出更高的耐热性，且差异程度与在生长季节适应后的蚂蚁之间观察到的相当。最后，我们没有发现不同种群在越冬实验开始到结束时蚁群大小变化方面存在差异的证据。总之，这些发现表明，尽管通常伴随着低温耐受性的丧失而进化出了更高的耐热性，但在生态相关的越冬条件下评估时，城市橡实蚁仍保留了低温生理性能的几个组成部分。我们的研究表明，在与季节相关的条件下测量生理性状对于理解对当代变暖的进化反应的原因和后果至关重要。
