Boratyński Jan S, Jefimow Małgorzata, Wojciechowski Michał S
Department of Animal Physiology, Nicolaus Copernicus University, ul. Lwowska 1, 87-100 Toruń, Poland
Department of Animal Physiology, Nicolaus Copernicus University, ul. Lwowska 1, 87-100 Toruń, Poland.
J Exp Biol. 2017 Sep 1;220(Pt 17):3154-3161. doi: 10.1242/jeb.159517. Epub 2017 Jun 12.
The duration of melatonin (MEL) secretion conveys information about day length and initiates a cascade of seasonal phenotypic adjustments in photoresponsive mammals. With shortening days, animals cease reproduction, minimize energy expenditure, enhance thermoregulatory capacity and adjust functioning of the hypothalamic-pituitary-adrenal (HPA) axis to match the winter increase in energy demands. Within each season, stress plays an important role in the flexible adjustments of a phenotype to environmental perturbations. Recent studies have shown that thermal reaction norms of energy metabolism were narrower in winter-acclimated Siberian hamsters, We tested the hypothesis that physiological changes occurring in response to prolonged MEL signals, including changes in the secretion of stress hormones, are responsible for the seasonal decrease in phenotypic flexibility of energy metabolism in photoresponsive mammals. To quantify reaction norms for basal metabolic rate (BMR) and cortisol (CORT) secretion, male Siberian hamsters maintained at a long (16 h:8 h light:dark) photoperiod were acclimated repeatedly for 12 days to 10 and 28°C. As predicted, the phenotypic flexibility of BMR decreased when animals were supplemented with MEL. However, at the same time, mean CORT concentration and the reaction norm for its secretion in response to changes in acclimation temperature increased. These results suggest that decreased sensitivity of HPA axis to CORT signal, rather than changes in CORT level itself, is responsible for the decreased phenotypic flexibility in photoresponsive species. Our results suggest that decreased phenotypic flexibility in winter, together with increased stress hormone secretion, make photosensitive species more vulnerable to climate change.
褪黑素（MEL）分泌的持续时间传递有关白昼长度的信息，并在光反应性哺乳动物中引发一系列季节性表型调整。随着白昼缩短，动物停止繁殖，将能量消耗降至最低，增强体温调节能力，并调整下丘脑 - 垂体 - 肾上腺（HPA）轴的功能，以适应冬季能量需求的增加。在每个季节内，应激在表型对环境扰动的灵活调整中起着重要作用。最近的研究表明，冬季适应的西伯利亚仓鼠能量代谢的热反应规范更窄。我们测试了这样一个假设，即响应延长的MEL信号而发生的生理变化，包括应激激素分泌的变化，是光反应性哺乳动物能量代谢表型灵活性季节性下降的原因。为了量化基础代谢率（BMR）和皮质醇（CORT）分泌的反应规范，将维持在长（16小时：8小时光照：黑暗）光周期的雄性西伯利亚仓鼠反复适应12天，温度分别为10和28°C。正如预测的那样，当给动物补充MEL时，BMR的表型灵活性下降。然而，与此同时，平均CORT浓度及其对应激适应温度变化的分泌反应规范增加。这些结果表明，HPA轴对CORT信号的敏感性降低，而非CORT水平本身的变化，是光反应性物种表型灵活性降低的原因。我们的结果表明，冬季表型灵活性的降低，以及应激激素分泌的增加，使光敏物种更容易受到气候变化的影响。
