Department of Zoology and Entomology, Rhodes University, Makhanda, 6139, South Africa; Department of Zoology, Nelson Mandela University, Port Elizabeth, 6031, South Africa.
Fitzpatrick Institute of African Ornithology, DST-NRF Centre of Excellence, University of Cape Town, Cape Town, 7701, South Africa; Centre for Functional Biodiversity, School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, South Africa.
J Therm Biol. 2021 Jan;95:102815. doi: 10.1016/j.jtherbio.2020.102815. Epub 2020 Dec 14.
For endotherms, maintaining body temperature during cold winters is energetically costly.Greater increase in winter maximum thermogenic capacity (M) has typically been correlated with improved cold tolerance. However, seasonal studies have shown equivocal direction change in basal metabolic rate (BMR) in winter, perhaps explained by latitude or phylogeny. We examined seasonal metabolic responses in the Cape rockjumper (Chaetops frenatus; "rockjumper"), a range-restricted mountain bird. We hypothesized that, given their mountain habitat preference, rockjumpers would be physiologically specialized for cooler air temperatures compared to other subtropical passerines. We measured body condition (using the ratio of M/tarsus), BMR, and M, in wild-living rockjumpers during winter and summer (n = 12 adults in winter -- 4 females, 8 males; n = 12 adults in summer -- 6 females, 6 males). We found birds had lesser BMR and thermal conductance, and greater M and body condition, in winter compared to summer. These changes may help rockjumpers conserve energy in winter while still allowing birds to produce more metabolic heat during the coldest air temperatures. When compared with existing data on avian seasonal metabolic adjustments, rockjumper BMR fit general patterns observed in passerines, but their M was low compared with other members of the oscine Passeriformes. These patterns may be explained by the narrow temperature range of their habitat not requiring cold-adjustment, or perhaps by their basal placement within passerine phylogeny. Further work on the physiological phenotypic plasticity in habitat specialists across different latitudinal zones and taxa is needed to better understand the relationship between metabolism, habitat, and phylogeny.
对于恒温动物来说，在寒冷的冬天维持体温是非常耗费能量的。冬季最大产热能力（M）的显著增加通常与对寒冷的耐受性提高有关。然而，季节性研究表明，基础代谢率（BMR）在冬季的变化方向不确定，这也许可以用纬度或系统发育来解释。我们研究了海角岩跳鹀（Chaetops frenatus；“岩跳鹀”）的季节性代谢反应，这是一种分布范围有限的山地鸟类。我们假设，鉴于它们对山地栖息地的偏好，岩跳鹀的生理机能可能适应了更凉爽的空气温度，与其他亚热带雀形目鸟类相比具有更强的适应能力。我们在冬季和夏季测量了野生岩跳鹀的身体状况（使用 M/跗跖骨的比值）、BMR 和 M，共有 12 只成年岩跳鹀参与研究，其中冬季 4 只雌鸟，8 只雄鸟；夏季 12 只成年岩跳鹀，6 只雌鸟，6 只雄鸟。我们发现，与夏季相比，冬季鸟类的 BMR 和热导率较低，而 M 和身体状况较好。这些变化可能有助于岩跳鹀在冬季节约能量，同时仍能在最冷的空气温度下产生更多代谢热量。与鸟类季节性代谢调整的现有数据相比，岩跳鹀的 BMR 符合雀形目鸟类观察到的一般模式，但与其他鸣禽的 M 相比，它们的 M 较低。这些模式可能是由于它们栖息地的温度范围较窄，不需要进行冷适应，或者可能是由于它们在鸣禽系统发育中的基础位置所致。需要对不同纬度带和分类群的栖息地专家的生理表型可塑性进行进一步研究，以更好地理解代谢、栖息地和系统发育之间的关系。
