Scantlebury M, Lovegrove B G, Jackson C R, Bennett N C, Lutermann H
Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa.
J Comp Physiol B. 2008 Sep;178(7):887-97. doi: 10.1007/s00360-008-0277-5. Epub 2008 Jun 4.
Although heterothermy (hibernation and torpor) is a common feature among mammals, there is debate over whether it is a derived or ancestral trait relative to endothermic homeothermy. Determination of the physiological characteristics of primitive mammals is central to understanding the evolution of endothermy. Moreover, evaluation of physiological mechanisms responsible for endothermic heat production [e.g. non-shivering thermogenesis (NST)] is key to understanding how early mammals responded to historical climate changes and colonised different geographical regions. Here we investigated the capacity for NST and heterothermy in the Hottentot golden mole, a basal eutherian mammal. NST was measured as the metabolic response to injections of noradrenalin and heterothermy by recording body temperature in free-ranging animals. We found that hibernation and torpor occurred and that the seasonal phenotypic adjustment of NST capacity was similar to that found in other placental mammals. Using phylogenetically independent contrasts, we compared measured values of NST with those obtained from the literature. This showed that all variation in NST was accounted for by differences in phylogeny and not zoogeography. These findings lend support to the observation that NST and heterothermy occur in the Afrotheria, the basal placental mammalian clade. Furthermore, this work suggests that heterothermy, rather than homeothermy is a plesiomorphic trait in mammals and supports the notion that NST mechanisms are phylogenetically ancient.
尽管异温性（冬眠和蛰伏）是哺乳动物的一个常见特征，但对于它相对于恒温性而言是一种衍生特征还是原始特征仍存在争议。确定原始哺乳动物的生理特征对于理解恒温性的进化至关重要。此外，评估负责产热的生理机制[例如非颤抖性产热（NST）]是理解早期哺乳动物如何应对历史气候变化以及在不同地理区域定殖的关键。在此，我们研究了南非金毛鼹（一种基础真兽类哺乳动物）的非颤抖性产热能力和异温性。通过记录自由活动动物的体温，将非颤抖性产热测量为对注射去甲肾上腺素的代谢反应以及异温性。我们发现了冬眠和蛰伏现象，并且非颤抖性产热能力的季节性表型调整与其他胎盘哺乳动物相似。使用系统发育独立对比，我们将非颤抖性产热的测量值与从文献中获得的值进行了比较。这表明非颤抖性产热的所有变化都是由系统发育差异而非动物地理学差异造成的。这些发现支持了在非洲兽类（基础胎盘哺乳动物类群）中存在非颤抖性产热和异温性的观察结果。此外，这项研究表明，异温性而非恒温性是哺乳动物的一个原始特征，并支持非颤抖性产热机制在系统发育上很古老的观点。
