Swanson David L, Garland Theodore
Department of Biology, University of South Dakota, Vermillion, South Dakota 57069, USA.
Evolution. 2009 Jan;63(1):184-94. doi: 10.1111/j.1558-5646.2008.00522.x. Epub 2008 Sep 18.
Summit metabolic rate (M(sum), maximum cold-induced metabolic rate) is positively correlated with cold tolerance in birds, suggesting that high M(sum) is important for residency in cold climates. However, the phylogenetic distribution of high M(sum) among birds and the impact of its evolution on current distributions are not well understood. Two potential adaptive hypotheses might explain the phylogenetic distribution of high M(sum) among birds. The cold adaptation hypothesis contends that species wintering in cold climates should have higher M(sum) than species wintering in warmer climates. The flight adaptation hypothesis suggests that volant birds might be capable of generating high M(sum) as a byproduct of their muscular capacity for flight; thus, variation in M(sum) should be associated with capacity for sustained flight, one indicator of which is migration. We collected M(sum) data from the literature for 44 bird species and conducted both conventional and phylogenetically informed statistical analyses to examine the predictors of M(sum) variation. Significant phylogenetic signal was present for log body mass, log mass-adjusted M(sum), and average temperature in the winter range. In multiple regression models, log body mass, winter temperature, and clade were significant predictors of log M(sum). These results are consistent with a role for climate in determining M(sum) in birds, but also indicate that phylogenetic signal remains even after accounting for associations indicative of adaptation to winter temperature. Migratory strategy was never a significant predictor of log M(sum) in multiple regressions, a result that is not consistent with the flight adaptation hypothesis.
巅峰代谢率（M总和，即最大冷诱导代谢率）与鸟类的耐寒性呈正相关，这表明高M总和对于在寒冷气候中栖息很重要。然而，鸟类中高M总和的系统发育分布及其进化对当前分布的影响尚不清楚。两种潜在的适应性假说或许可以解释鸟类中高M总和的系统发育分布。冷适应假说认为，在寒冷气候中越冬的物种应比在温暖气候中越冬的物种具有更高的M总和。飞行适应假说表明，会飞的鸟类可能能够产生高M总和，作为其飞行肌肉能力的副产品；因此，M总和的变化应与持续飞行能力相关，其中一个指标就是迁徙。我们从文献中收集了44种鸟类的M总和数据，并进行了传统的和基于系统发育的统计分析，以检验M总和变化的预测因素。在对数体重、对数质量调整后的M总和以及冬季分布范围内的平均温度方面，存在显著的系统发育信号。在多元回归模型中，对数体重、冬季温度和进化枝是对数M总和的显著预测因素。这些结果与气候在决定鸟类M总和方面的作用一致，但也表明，即使在考虑了表明适应冬季温度的关联之后，系统发育信号仍然存在。在多元回归中，迁徙策略从未成为对数M总和的显著预测因素，这一结果与飞行适应假说不一致。
