Quantifying the repeated evolution of insect raptorial forelegs

Insect raptorial forelegs, which function in prey capture, evolved independently in several lineages. The common function may lead to morphological similarity; however, few studies have examined the morphological evolution of raptorial forelegs across insect lineages. We quantified morphological evolution in insect raptorial forelegs and other body parts based on comparative analyses of their shape, as quantified by segmental dimensions, across six lineages. We characterized three aspects of the evolution of morphological similarity in a morphospace: (1) a shift in mean shape, (2) a reduction in shape variation, and (3) similarity in the direction of evolution. The foreleg and forebody shapes exhibited low-to-moderate similarity in the direction of evolution with respect to the gain of raptorial function; however, significant patterns were not detected for other characteristics. Thus, the evolution of insect raptorial forelegs was not parallel or convergent but involved morphological diversity among lineages, indicating a many-to-one mapping of shape to function. We detected correlated patterns of evolution between the foreleg and forebody, reflecting functional relationships possibly related to hunting and depth perception. Furthermore, the direction of evolution differed between terrestrial and aquatic habitats. This study provides novel insights into the evolutionary processes leading to functional and morphological similarities.