Department of Evolution, Ecology and Organismal Biology, Ohio State University, Aronoff Laboratory, 318 W 12th Avenue, Columbus, OH 43210, USA.
J Exp Biol. 2012 May 15;215(Pt 10):1662-9. doi: 10.1242/jeb.065144.
Attributes of an animal's life history, such as reproductive rate or longevity, typically fall along a 'slow-fast' continuum. Animals at the fast end of this continuum, such as temperate birds, are thought to experience high rates of mortality and invest more resources in reproduction, whereas animals at the slow end, such as tropical birds, live longer, have fewer offspring and invest more resources in self-maintenance. We have previously shown that tropical birds, compared with temperate species, have a reduced basal (BMR) and peak metabolic rate (PMR), patterns consistent with a slow pace of life. Here, we elucidate a fundamental linkage between the smaller mass of central organs of tropical species and their reduced BMR, and between their smaller flight muscles and reduced PMR. Analyses of up to 408 species from the literature showed that the heart, flight muscles, liver, pancreas and kidneys were smaller in tropical species. Direct measurements on 49 species showed smaller heart, lungs, flight muscles, liver, kidneys, ovaries and testes in tropical species, as well as lower feather mass. In combination, our results indicate that the benign tropical environment imposes a relaxed selection pressure on high levels of sustained metabolic performance, permitting species to reduce the mass of organs that are energetically costly to maintain. Brain, gizzard and intestine were exceptions, even though energy turnover of brain and intestine are high. Feather mass was 37% lower in tropical species compared with similar-sized temperate birds, supporting the idea that temperate birds require more insulation for thermoregulation.
动物的生活史特征，如繁殖率或寿命，通常沿着“慢-快”连续体分布。处于该连续体快速端的动物，如温带鸟类，被认为死亡率较高，并且在繁殖上投入更多资源，而处于慢速端的动物，如热带鸟类，寿命更长，后代更少，并且在自我维持上投入更多资源。我们之前已经表明，与温带物种相比，热带鸟类的基础代谢率（BMR）和峰值代谢率（PMR）较低，这与缓慢的生活节奏模式一致。在这里，我们阐明了热带物种的中心器官质量较小与其 BMR 降低之间，以及它们的飞行肌肉较小与其 PMR 降低之间的基本联系。对文献中多达 408 种物种的分析表明，热带物种的心脏、飞行肌肉、肝脏、胰腺和肾脏较小。对 49 种物种的直接测量表明，热带物种的心脏、肺、飞行肌肉、肝脏、肾脏、卵巢和睾丸较小，羽毛质量也较低。总的来说，我们的结果表明，良性热带环境对高水平持续代谢性能的选择压力较小，允许物种减少维持器官所需的能量成本。大脑、砂囊和肠道是例外，尽管大脑和肠道的能量周转率很高。与相似大小的温带鸟类相比，热带鸟类的羽毛质量低 37%，这支持了温带鸟类需要更多隔热来调节体温的观点。
