Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York, USA.
mBio. 2010 Nov 9;1(5):e00212-10. doi: 10.1128/mBio.00212-10.
Endothermy and homeothermy are mammalian characteristics whose evolutionary origins are poorly understood. Given that fungal species rapidly lose their capacity for growth above ambient temperatures, we have proposed that mammalian endothermy enhances fitness by creating exclusionary thermal zones that protect against fungal disease. According to this view, the relative paucity of invasive fungal diseases in immunologically intact mammals relative to other infectious diseases would reflect an inability of most fungal species to establish themselves in a mammalian host. In this study, that hypothesis was tested by modeling the fitness increase with temperature versus its metabolic costs. We analyzed the tradeoff involved between the costs of the excess metabolic rates required to maintain a body temperature and the benefit gained by creating a thermal exclusion zone that protects against environmental microbes such as fungi. The result yields an optimum at 36.7°C, which closely approximates mammalian body temperatures. This calculation is consistent with and supportive of the notion that an intrinsic thermally based resistance against fungal diseases could have contributed to the success of mammals in the Tertiary relative to that of other vertebrates.
温血和恒温是哺乳动物的特征，其进化起源尚不清楚。鉴于真菌物种在环境温度以上会迅速失去生长能力，我们提出哺乳动物的恒温通过创造排斥热区来提高适应性，从而防止真菌疾病。根据这一观点，与其他传染病相比，在免疫功能健全的哺乳动物中侵袭性真菌感染的相对缺乏反映了大多数真菌物种无法在哺乳动物宿主中建立自身。在这项研究中，通过对温度与代谢成本的关系进行建模，检验了这一假设。我们分析了维持体温所需的额外代谢率的成本与通过创造热隔离区来抵御真菌等环境微生物的收益之间的权衡。结果在 36.7°C 处产生了最佳值，这与哺乳动物的体温非常接近。这一计算结果与以下观点一致，并支持了这样一种观点，即对真菌病的内在热抗性可能有助于哺乳动物在第三纪相对于其他脊椎动物的成功。
