Swanson David, Zhang Yufeng, Liu Jin-Song, Merkord Christopher L, King Marisa O
Department of Biology, University of South Dakota, 414 E Clark St., Vermillion, SD 57069, USA.
J Exp Biol. 2014 Mar 15;217(Pt 6):866-75. doi: 10.1242/jeb.096677.
Seasonal phenotypic flexibility in small birds produces a winter phenotype with elevated maximum cold-induced metabolic rates (=summit metabolism, Msum). Temperature and photoperiod are candidates for drivers of seasonal phenotypes, but their relative impacts on metabolic variation are unknown. We examined photoperiod and temperature effects on Msum, muscle masses and activities of key catabolic enzymes in winter dark-eyed juncos (Junco hyemalis). We randomly assigned birds to four treatment groups varying in temperature (cold=3°C; warm=24°C) and photoperiod [short day (SD)=8 h:16 h light:dark; long day (LD)=16 h:8 h light:dark] in a two-by-two design. We measured body mass (Mb), flight muscle width and Msum before and after 3 and 6 weeks of acclimation, and flight muscle and heart masses after 6 weeks. Msum increased for cold-exposed, but not for warm-exposed, birds. LD birds gained more Mb than SD birds, irrespective of temperature. Flight muscle size and mass did not differ significantly among groups, but heart mass was larger in cold-exposed birds. Citrate synthase, carnitine palmitoyl transferase and β-hydroxyacyl Co-A dehydrogenase activities in the pectoralis were generally higher for LD and cold groups. The cold-induced changes in Msum and heart mass parallel winter changes for small birds, but the larger Mb and higher catabolic enzyme activities in LD birds suggest photoperiod-induced changes associated with migratory disposition. Temperature appears to be a primary driver of flexibility in Msum in juncos, but photoperiod-induced changes in Mb and catabolic enzyme activities, likely associated with migratory disposition, interact with temperature to contribute to seasonal phenotypes.
小型鸟类的季节性表型灵活性会产生一种冬季表型，其最大冷诱导代谢率（即巅峰代谢率，Msum）升高。温度和光周期是季节性表型的驱动因素候选者，但它们对代谢变化的相对影响尚不清楚。我们研究了光周期和温度对冬季暗眼灯草鹀（Junco hyemalis）的Msum、肌肉质量以及关键分解代谢酶活性的影响。我们采用二乘二设计，将鸟类随机分为四个处理组，温度（冷=3°C；暖=24°C）和光周期[短日照（SD）=8小时光照：16小时黑暗；长日照（LD）=16小时光照：8小时黑暗]各不相同。我们在适应3周和6周前后测量了体重（Mb）、飞行肌宽度和Msum，并在6周后测量了飞行肌和心脏质量。暴露于寒冷环境的鸟类Msum增加，而暴露于温暖环境的鸟类则没有。无论温度如何，长日照鸟类比短日照鸟类增加的体重更多。各组之间飞行肌大小和质量没有显著差异，但暴露于寒冷环境的鸟类心脏质量更大。长日照组和寒冷组胸肌中的柠檬酸合酶、肉碱棕榈酰转移酶和β-羟酰基辅酶A脱氢酶活性通常更高。Msum和心脏质量的冷诱导变化与小型鸟类的冬季变化相似，但长日照鸟类更大的体重和更高的分解代谢酶活性表明与迁徙倾向相关的光周期诱导变化。温度似乎是灯草鹀Msum灵活性的主要驱动因素，但光周期诱导的体重和分解代谢酶活性变化，可能与迁徙倾向有关，与温度相互作用，共同促成季节性表型。
