Department of Zoology, Nelson Mandela University, Gqeberha 6031, South Africa.
Department of Molecular Biosciences, The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, SE-106 91 Stockholm, Sweden.
J Exp Biol. 2022 Jul 1;225(13). doi: 10.1242/jeb.243860. Epub 2022 Jul 4.
Small mammals undergo thermoregulatory adjustments in response to changing environmental conditions. Whereas small heterothermic mammals can employ torpor to save energy in the cold, homeothermic species must increase heat production to defend normothermia through the recruitment of brown adipose tissue (BAT). Here, we studied thermoregulatory adaptation in an obligate homeotherm, the African striped mouse (Rhabdomys pumilio), captured from a subpopulation living in a mesic, temperate climate with marked seasonal differences. Basal metabolic rate (BMR), non-shivering thermogenesis (NST) and summit metabolic rate (Msum) increased from summer to winter, with NST and Msum already reaching maximal rates in autumn, suggesting seasonal preparation for the cold. Typical of rodents, cold-induced metabolic rates were positively correlated with BAT mass. Analysis of cytochrome c oxidase (COX) activity and UCP1 content, however, demonstrated that thermogenic capacity declined with BAT mass. This resulted in seasonal differences in NST being driven by changes in BMR. The increase in BMR was supported by a comprehensive anatomical analysis of metabolically active organs, revealing increased mass proportions in the cold season. The thermoregulatory response of R. pumilio was associated with the maintenance of body mass throughout the year (48.3±1.4 g), contrasting large summer-winter mass reductions often observed in Holarctic rodents. Collectively, bioenergetic adaptation of this Afrotropical rodent involves seasonal organ adjustments influencing BMR, combined with a constant thermogenic capacity dictated by trade-offs in the thermogenic properties of BAT. Arguably, this high degree of plasticity was a response to unpredictable cold spells throughout the year. Consequently, the reliance on such a resource-intensive thermoregulatory strategy may expose more energetic vulnerability in changing environments of food scarcity and extreme weather conditions due to climate change, with major ramifications for survival of the species.
小型哺乳动物会根据环境变化进行体温调节适应。小型异温动物可以通过进入蛰伏状态来节省在寒冷环境中的能量，而恒温动物则必须通过募集棕色脂肪组织（BAT）来增加热量产生以维持正常体温。在这里，我们研究了一种强制性恒温动物——非洲条纹鼠（Rhabdomys pumilio）的体温调节适应能力，这些非洲条纹鼠来自于一个生活在中纬度、气候湿润且具有明显季节性差异的亚种群。基础代谢率（BMR）、非颤抖性产热（NST）和峰值代谢率（Msum）从夏季到冬季逐渐增加，其中 NST 和 Msum 在秋季已经达到最大速率，这表明它们已经为寒冷季节做好了准备。与啮齿动物典型的情况一样，冷诱导代谢率与 BAT 质量呈正相关。然而，细胞色素 c 氧化酶（COX）活性和 UCP1 含量的分析表明，产热能力随 BAT 质量的下降而下降。这导致 NST 的季节性差异是由 BMR 的变化驱动的。BMR 的增加得到了对代谢活跃器官的全面解剖分析的支持，该分析显示在寒冷季节中器官的质量比例增加。R. pumilio 的体温调节反应与全年保持体重有关（48.3±1.4 g），这与 Holarctic 啮齿动物经常观察到的夏季到冬季体重大幅减少形成对比。总的来说，这种非洲热带啮齿动物的生物能量适应涉及季节性器官调整，影响 BMR，同时结合 BAT 产热特性的权衡来维持恒定的产热能力。可以说，这种高度的可塑性是对全年不可预测的寒冷期的反应。因此，由于气候变化导致食物短缺和极端天气条件下的环境变化，这种依赖资源密集型体温调节策略的物种可能会面临更大的能量脆弱性，这对该物种的生存将产生重大影响。
