Data from: Moth body size increases with elevation along a complete tropical elevational gradient for two hyperdiverse clades

The body size of an animal is probably its most important functional trait. For arthropods, environmental drivers of body size variation are still poorly documented and understood, especially in tropical regions. We use a unique dataset for two species-rich, phylogenetically independent moth taxa (Lepidoptera: Geometridae; Arctiinae), collected along an extensive tropical elevational gradient in Costa Rica, to investigate the correlates and possible causes of body-size variation. We studied 15,047 specimens (794 species) of Geometridae and 4,167 specimens (308 species) of Arctiinae to test the following hypotheses: 1) body size increases with decreasing ambient temperature, as predicted by the temperature-size rule; 2) body size increases with increasing rainfall and primary productivity, as predicted from considerations of starvation resistance; and 3) body size scales allometrically with wing area, as elevation increases, such that wing loading (the ratio of body size to wing area) decreases with increasing elevation to compensate for lower air density. To test these hypotheses, we examined forewing length as a proxy for body size in relation to ambient temperature, rainfall, vegetation index and elevation as explanatory variables in linear and polynomial spatial regression models. We analysed our data separately for males and females using two principal approaches: mean forewing length of species at each site, and mean forewing length of complete local assemblages, weighted by abundance. Body size consistently increased with elevation in both taxa, both approaches, both sexes, and also within species. Temperature was the best predictor for this pattern (-0.98 < r < -0.74), whereas body size was uncorrelated or weakly correlated with rainfall and enhanced vegetation index. Wing loading increased with elevation. Our results support the temperature-size rule as an important mechanism for body size variation in arthropods along tropical elevational gradients, whereas starvation resistance and optimization of flight mechanics seem to be of minor importance.

动物的体型或许是其最为关键的功能性状。针对节肢动物而言，体型变异的环境驱动因子仍鲜有记录与阐释，在热带区域尤为如此。本研究依托在哥斯达黎加广泛热带海拔梯度上采集的、针对两个物种丰富且系统发育独立的蛾类类群（鳞翅目：尺蛾科；灯蛾亚科）的独特数据集，探究体型变异的相关关联因子与潜在成因。本研究共分析尺蛾科的15047号标本（涵盖794个物种）与灯蛾亚科的4167号标本（涵盖308个物种），以验证以下三项假说：其一，正如温度-体型法则（temperature-size rule）所预测，体型会随环境温度降低而增大；其二，基于抗饥饿性的相关理论预测，体型会随降雨量与初级生产力提升而增大；其三，随着海拔升高，体型与翅面积呈异速缩放关系，即翼载荷（wing loading，即体型与翅面积的比值）随海拔升高而降低，以补偿空气密度降低带来的影响。为验证上述假说，本研究以前翅长作为体型的替代指标，将环境温度、降雨量、增强型植被指数与海拔作为解释变量，构建线性与多项式空间回归模型，分析体型与各变量间的关联。本研究采用两种核心分析方法，分别针对雌雄个体展开数据处理：一是以各采样点内物种的平均前翅长为指标，二是以完整本地类群组合的平均前翅长为指标，并以种群丰度进行加权。两类蛾类、两种分析方法、雌雄个体以及物种内部的体型均随海拔升高呈现一致的增大趋势。环境温度是该体型变化模式的最佳预测因子（相关系数r的范围为-0.98至-0.74），而体型与降雨量及增强型植被指数则无关联或仅存在弱相关。翼载荷随海拔升高而增大。本研究结果证实，温度-体型法则是热带海拔梯度上节肢动物体型变异的重要驱动机制，而抗饥饿性与飞行力学优化的作用则相对次要。