Department of Zoology, Miami University, Oxford, OH 45056, USA.
J Exp Biol. 2012 Jul 15;215(Pt 14):2418-24. doi: 10.1242/jeb.061168.
Northern cardinals (Cardinalis cardinalis) are faced with energetically expensive seasonal challenges that must be met to ensure survival, including thermoregulation in winter and reproductive activities in summer. Contrary to predictions of life history theory that suggest breeding metabolic rate should be the apex of energetic effort, winter metabolism exceeds that during breeding in several temperate resident bird species. By examining whole-animal, tissue and cellular function, we ask whether seasonal acclimatization is accomplished by coordinated phenotypic plasticity of metabolic systems. We measured summit metabolism (V(O(2),sum)), daily energy expenditure (DEE) and muscle oxidative capacity under both winter (December to January) and breeding (May to June) conditions. We hypothesize that: (1) rates of energy utilization will be highest in the winter, contrary to predictions based on life history theory, and (2) acclimatization of metabolism will occur at multiple levels of organization such that birds operate with a similar metabolic ceiling during different seasons. We measured field metabolic rates using heart rate telemetry and report the first daily patterns in avian field metabolic rate. Patterns of daily energy use differed seasonally, primarily as birds maintain high metabolic rates throughout the winter daylight hours. We found that DEE and V(O(2),sum) were significantly greater and DEE occurred at a higher fraction of maximum metabolic capacity during winter, indicating an elevation of the metabolic ceiling. Surprisingly, there were no significant differences in mass or oxidative capacity of skeletal muscle. These data, highlighting the importance of examining energetic responses to seasonal challenges at multiple levels, clearly reject life history predictions that breeding is the primary energetic challenge for temperate zone residents. Further, they indicate that metabolic ceilings are seasonally flexible as metabolic effort during winter thermoregulation exceeds that of breeding.
北红雀（Cardinalis cardinalis）面临着季节性的能量挑战，必须满足这些挑战才能确保生存，包括冬季的体温调节和夏季的繁殖活动。与生活史理论的预测相反，该理论表明繁殖代谢率应该是能量投入的顶点，但在几种温带留鸟物种中，冬季代谢率超过了繁殖期间的代谢率。通过检查整体动物、组织和细胞功能，我们询问季节性适应是否通过代谢系统的协调表型可塑性来实现。我们测量了冬季（12 月至 1 月）和繁殖期（5 月至 6 月）的顶峰代谢率（V(O(2),sum)）、每日能量支出（DEE）和肌肉氧化能力。我们假设：（1）能量利用的速度在冬季最高，与基于生活史理论的预测相反，（2）代谢的适应将发生在多个组织水平上，使得鸟类在不同季节以相似的代谢上限运作。我们使用心率遥测技术测量了野外代谢率，并报告了鸟类野外代谢率的第一个每日模式。每日能量使用模式季节性差异很大，主要是因为鸟类在整个冬季白天保持高代谢率。我们发现，DEE 和 V(O(2),sum) 在冬季显著增加，并且 DEE 在最大代谢能力的更高分数下发生，表明代谢上限的升高。令人惊讶的是，骨骼肌的质量或氧化能力没有显著差异。这些数据强调了在多个层次上检查季节性挑战的能量反应的重要性，明确拒绝了繁殖是温带居民主要能量挑战的生活史预测。此外，它们表明代谢上限具有季节性灵活性，因为冬季体温调节的代谢努力超过了繁殖期间的代谢努力。
