Tabh Joshua K R, Persson Elin, Correia Maria, Cuív Ciarán Ó, Thoral Elisa, Nord Andreas
Department of Biology, Lund University, Lund, Sweden.
Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland.
Commun Biol. 2025 May 7;8(1):707. doi: 10.1038/s42003-025-08131-7.
Amassing evidence indicates that vertebrates across the globe are shrinking and changing shape concurrent with rising temperatures. Ecogeographical theories assert that these changes should provide thermoregulatory benefits by easing heat dissipation, however, thermophysical models underpinning such theories are highly simplified and lack empirical validation. Using data from three temperature-manipulation experiments, we quantified the contributions of body size and appendage lengths toward thermoregulatory performance in Japanese quail, while simultaneously querying neutral plasticity as an alternative driver of avian shape-shifts. In the cold, body mass and leg length (here, tarsus length) influenced energy costs of warming, but only among juveniles. In the warmth, smaller body sizes, longer legs and longer bills independently reduced energy and water costs of cooling across ages, but whole-body phenotypes necessary to provide even moderate thermoregulatory benefits were rare (2.5%) and required large departures from allometry. Last, rearing in the warmth reduced body sizes and increased appendage lengths comparable to recent changes observed in nature, but emergent morphologies provided no clear thermoregulatory benefit. Our findings question whether shrinking and shape-shifting are indeed easing thermoregulation in birds or reflect selection for such. Neutral plasticity, or relaxed selection against small body size in juveniles, may better explain recent avian shape-shifting.
越来越多的证据表明，随着全球气温上升，世界各地的脊椎动物体型在变小，形态也在发生变化。生态地理学理论认为，这些变化应通过促进散热来提供体温调节益处，然而，支撑此类理论的热物理模型高度简化，缺乏实证验证。利用来自三个温度控制实验的数据，我们量化了日本鹌鹑的体型和附肢长度对体温调节性能的贡献，同时探究中性可塑性作为鸟类形态变化的另一种驱动因素。在寒冷环境中，体重和腿长（此处为跗跖长度）影响升温的能量消耗，但仅在幼鸟中存在这种情况。在温暖环境中，较小的体型、较长的腿和较长的喙能独立降低各年龄段降温的能量和水分消耗，但能提供哪怕适度体温调节益处的全身表型很少见（2.5%），且需要大幅偏离异速生长规律。最后，在温暖环境中饲养会使体型变小，附肢长度增加，这与自然界中最近观察到的变化类似，但新出现的形态并未带来明显的体温调节益处。我们的研究结果质疑体型缩小和形态变化是否真的有助于鸟类的体温调节，或者是否反映了对此的选择。中性可塑性，或者对幼鸟小体型的选择放松，可能更好地解释了近期鸟类的形态变化。
