Noakes Matthew J, Wolf Blair O, McKechnie Andrew E
DST-NRF Centre of Excellence at the Percy FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa.
UNM Biology Department, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA.
J Exp Biol. 2016 Mar;219(Pt 6):859-69. doi: 10.1242/jeb.132001. Epub 2016 Jan 19.
Intraspecific variation in avian thermoregulatory responses to heat stress has received little attention, despite increasing evidence that endothermic animals show considerable physiological variation among populations. We investigated seasonal (summer versus winter) variation in heat tolerance and evaporative cooling in an Afrotropical ploceid passerine, the white-browed sparrow-weaver (Plocepasser mahali; ∼ 47 g) at three sites along a climatic gradient with more than 10 °C variation in mid-summer maximum air temperature (Ta). We measured resting metabolic rate (RMR) and total evaporative water loss (TEWL) using open flow-through respirometry, and core body temperature (Tb) using passive integrated transponder tags. Sparrow-weavers were exposed to a ramped profile of progressively higher Ta between 30 and 52 °C to elicit maximum evaporative cooling capacity (N=10 per site per season); the maximum Ta birds tolerated before the onset of severe hyperthermia (Tb ≈ 44 °C) was considered to be their hyperthermia threshold Ta (Ta,HT). Our data reveal significant seasonal acclimatisation of heat tolerance, with a desert population of sparrow-weavers reaching significantly higher Ta in summer (49.5 ± 1.4 °C, i.e. higher Ta,HT) than in winter (46.8 ± 0.9 °C), reflecting enhanced evaporative cooling during summer. Moreover, desert sparrow-weavers had significantly higher heat tolerance and evaporative cooling capacity during summer compared with populations from more mesic sites (Ta,HT=47.3 ± 1.5 and 47.6 ± 1.3 °C). A better understanding of the contributions of local adaptation versus phenotypic plasticity to intraspecific variation in avian heat tolerance and evaporative cooling capacity is needed for modelling species' responses to changing climates.
尽管越来越多的证据表明恒温动物在种群间表现出相当大的生理差异，但鸟类对热应激的体温调节反应中的种内变异却很少受到关注。我们调查了一种非洲热带织雀科雀形目鸟类——白眉麻雀织雀（Plocepasser mahali；约47克）在沿着气候梯度的三个地点的耐热性和蒸发散热的季节性（夏季与冬季）变化，这些地点在仲夏最高气温（Ta）上有超过10°C的差异。我们使用开放式流通呼吸测定法测量静息代谢率（RMR）和总蒸发失水量（TEWL），并使用被动集成应答器标签测量核心体温（Tb）。将麻雀织雀暴露在30至52°C之间逐渐升高的Ta斜坡曲线中，以激发最大蒸发散热能力（每个季节每个地点N = 10）；在严重体温过高（Tb≈44°C）开始之前鸟类耐受的最高Ta被认为是它们的体温过高阈值Ta（Ta,HT）。我们的数据揭示了耐热性的显著季节性适应，沙漠地区的麻雀织雀种群在夏季达到的Ta（49.5±1.4°C，即更高的Ta,HT）显著高于冬季（46.8±0.9°C），这反映了夏季蒸发散热的增强。此外，与来自更多湿润地区的种群相比，沙漠麻雀织雀在夏季具有显著更高的耐热性和蒸发散热能力（Ta,HT = 47.3±1.5和47.6±1.3°C）。为了模拟物种对气候变化的反应，需要更好地理解局部适应与表型可塑性对鸟类耐热性和蒸发散热能力种内变异的贡献。
