The mouthparts of the adult dragonfly Anax imperator (Insecta: Odonata), functional morphology and feeding kinematics

Raw data of video footage

Abstract:

Insects evolved various specialized mouthparts. We present an exemplary study on the mouthparts of adult Anax imperator, one of the largest odonates found in Central Europe. Like all adult dragonflies, A. imperator possesses carnivorous-type of biting-chewing mouthparts. To gain insights into the feeding process, behaviour and kinematics, living specimens were filmed during feeding using synchronized high-speed videography. Additionally, the maximum angles of movement were measured using a measuring microscope and combined with data from micro-computed tomography (µCT). The resulting visualizations of the 3D-geometry of each mouthpart were used to study their anatomy and complement the only descriptive knowledge of muscles in A. imperator to date. Furthermore, CLSM-projections allow for estimation of differences in the material composition of the mouthparts' cuticle. By combining all methods, we can highlight possible functions and underlying biomechanics of each mouthpart. With regards to behavior, we analyzed the concerted movements of the mouthparts; two different types of cyclical feeding behavior were observed, which we refer to as “biting” and “chewing” throughout this study. Unique behavior of the mouthparts during feeding is active participation by the labrum and distinct movement by the maxillary laciniae. We aim to elucidate the complex movements of the mouthparts and their functioning by combining detailed information on (1) in vivo movement behavior (supplemented with physiological angle approximations), (2) movement ability provided by morphology (morphological movement angles), (3) 3D-anatomy, and (4) cuticle composition estimates. Furthermore, we present a study design that interlinks multiple methods for broad scale comparative studies in insects. This may allow for biomechanical and functional comparison of different eco-types of biting-chewing mouthparts in insects with varying food preferences and feeding habits. However, our approach only represents a starting point that can and should be further optimized and enhanced.