Morphological evolution of bird wings follows a mechanical sensitivity gradient determined by the aerodynamics of flapping flight

Abstract

The physical principles that govern the function of biological structures also mediate their evolution, but the evolutionary drivers of morphological traits within complex structures can be difficult to predict. We used morphological traits measured from 1096 3-dimensional bird wing scans from 178 species to test how two frameworks for relating morphology to evolution interact. We examined whether the modular organization of the wing into handwing and armwing regions, or the relationship between trait morphology and functional output (i.e. mechanical sensitivity, driven here by flapping flight aerodynamics) dominate evolutionary rate ({sigma}2) and mode. Our results support discretization of the armwing and handwing as morphological modules, but morphological disparity and{sigma} 2 varied continuously with the mechanical sensitivity gradient and were not modular. Thus, mechanical sensitivity should be considered an independent driver of evolutionary dynamics, distinct from morphological modularity. TeaserMechanical sensitivity drives wing shape evolution in birds and may be fundamental to the evolution of biomechanical systems.