Morphological constraints in hymenopteran forewings limit flight efficiency optimization.

The evolution of wings and flapping flight was integral to the radiation of Pterygota, but little is known about the factors underpinning the morphological disparity of insect wings. We use a theoretical morphospace approach to investigate forewing morphology across the four major clades in Hymenoptera (sawflies, wasps, bees and ants). Using elliptical Fourier analysis we quantified the outline of 298 forewings and generated 494 theoretical forms plotted within a morphospace. Theoretical forewing shapes were analysed across three metrics for flight performance that are antagonistic and ranked subsequently according to their functional optimization. The results show theoretical wings with larger, rounder apical tips were most optimized for a trade-off between reducing induced drag and increasing both lift production and breakage resistance. Empirical forewings cluster in a suboptimal region of theoretical morphospace exhibiting moderate flight performance. Phylomorphospace analysis reveals high levels of convergence in wing shapes across Hymenoptera, with a weak but significant phylogenetic signal. Regression analyses found significant allometric covariation but no significant relationship with environmental measures (temperature and precipitation) on forewing morphology. These findings demonstrate that hymenopteran wing morphologies are not optimized for flight function. Instead, function and allometry act in concert to constrain the variation of hymenopteran forewing morphologies.