Diptera flight diversity is shaped by aerodynamic constraints, scaling, and evolutionary trade-offs

Flight has been a key innovation in insect evolution, yet the selective and mechanistic forces shaping their flight motor systems remain poorly understood. Here, we present a comprehensive comparative analysis of Diptera (true flies), integrating morphology, wingbeat kinematics, and aerodynamics within a phylogenetic framework. We quantified morphology in 133 species spanning the Dipteran phylogenetic and size range, and for a subset of 46 species, we combined high-speed stereoscopic videography with computational fluid dynamics (CFD) to characterize wingbeat kinematics and aerodynamic performance, respectively. Our results reveal that morphology is strongly structured by phylogeny, whereas wingbeat kinematics are broadly conserved across Diptera, reflecting dominant aerodynamic constraints. Two basal lineages, Culicomorpha (mosquitoes and midges) and Tipulomorpha (crane flies), exhibit strikingly divergent kinematics and aerodynamics, suggesting lineage-specific selective pressures. Scaling analyses show that smaller species compensate for reduced aerodynamic force production efficacy through relatively larger wings, and higher wingbeat frequencies. Moreover, miniaturization is constrained by increased viscous drag at low Reynolds numbers, causing a plateau in aerodynamic power reduction with decreasing size. We further demonstrate that mosquitoes exhibit disproportionately high aerodynamic and acoustic power, coupled with enlarged flight musculature, consistent with sexual selection favoring acoustic signaling during in-swarm mating. This trade-off highlights how reproductive pressures can override aerodynamic efficiency. By integrating comparative morphology, kinematics, and aerodynamics across a major insect radiation, our study uncovers the interplay between physical scaling laws, aerodynamic constraints, and ecological pressures in shaping the evolution of animal flight. These findings provide a mechanistic framework for understanding how complex locomotor systems diversify under multiple selective forces.