Musculoskeletal modeling of the dragonfly mandible system as an aid to understanding the role of single muscles in an evolutionary context

Insects show a high variety of mouthpart and muscle configurations, however, their mouthpart kinematics and muscle activation patterns are known fragmentary. Understanding the role of muscle groups during movement and comparing them between insect groups could yield insights into evolutionary patterns and functional constraints. Here, we develop a mathematical inverse dynamic model including distinct muscles for an insect head-mandible-muscle complex based on micro computed tomography (µCT) data and bite force measurements. With the advent of µCT it is now possible to obtain precise spatial information about muscle attachment areas and head capsule construction in insects. Our model shows a distinct activation pattern for certain fiber groups potentially related to a geometry dependent optimization. Muscle activation patterns suggest that intramandibular muscles play a minor role for bite force generation which is a potential reason for their loss in several lineages of higher insects. Our model is in agreement with previous studies investigating fast and slow muscle fibers and is able to resolve the spatio-temporal activation patterns of these different muscle types in insects. The model used here has a high potential for comparative large scale analyses on the role of different muscle setups and head capsule designs in the megadiverse insects in order to aid our understanding of insect head capsule and mouthpart evolution under mechanical constraints.