Data from: Large brains, small guts: the expensive tissue hypothesis supported within anurans

Brain size differs substantially among species and several hypotheses have been proposed to explain the evolution of brain size. Because the brain is among the most energetically expensive organs in the vertebrate body, trade-offs have been hypothesized to exert constraints on brain size evolution. Prominently, the expensive-tissue hypothesis (ETH) proposes that reducing the size of another expensive organ, such as the gut, should compensate for the cost of a large brain. But energetic constraints may also drive covariation between the brain and other costly traits such as body maintenance, locomotion or reproduction, as formulated in the energy trade-off hypothesis. To date, these hypotheses have mainly been tested in homoeothermic animals and within the ectothermic animals, primarily in fishes. Here, we undertake a comparative test of the interplay between energetic limitations and brain size evolution within amphibians. After controlling for phylogenetic relationships and body size, we find a negative correlation between brain mass and the length of the digestive tract within 30 species of anurans. We further find that the evolution of large brain size is accompanied by an increase in female reproductive investment into egg size. Our results suggest that the evolution of brain size follows general patterns across vertebrate clades.

不同物种间的脑容量差异显著，学界已提出多种假说以阐释脑容量的演化机制。由于大脑是脊椎动物体内能量消耗最高的器官之一，权衡（trade-off）假说认为其会对脑容量演化施加约束。其中极具影响力的昂贵组织假说（Expensive-Tissue Hypothesis, ETH）提出，缩减另一高耗能器官（如肠道）的体积，可补偿大型大脑所需的代谢成本。而正如能量权衡假说（Energy Trade-off Hypothesis）所阐述的，能量约束也可能推动大脑与其他高耗能性状（如机体维持、运动或繁殖）之间产生协同变异。迄今为止，上述假说主要在恒温动物（homoeothermic animals）以及变温动物（ectothermic animals，尤以鱼类为代表）中得到验证。本研究针对两栖动物类群，开展了能量限制与脑容量演化之间相互作用的比较检验。在控制系统发育关系（phylogenetic relationships）与体型变量后，我们在30种无尾目（anurans）物种中发现，脑质量与消化道长度呈负相关关系。进一步分析显示，大型脑容量的演化伴随雌性对卵体积的繁殖投入增加。本研究结果表明，脑容量的演化遵循脊椎动物各演化支（clades）共有的通用模式。