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

Abstract

Insects evolved differently specialized mouthparts. We study 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, behavior 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.The resulting visualizations of the 3D-geometry of each mouthpart were used to study their anatomy and complement the existing descriptive knowledge of muscles in A. imperator to date. Furthermore, confocal laser scanning microscopy-projections allow for estimation of differences in the material composition of the mouthparts' cuticle. By combining all methods, we analyze possible functions and underlying biomechanics of each mouthpart. We also analyzed the concerted movements of the mouthparts; 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.

A switchable joint in the head of dragonfly larvae (Insecta: Odonata) as key to the multifunctionality of the prehensile labial mask

“…The results clearly show that a prehensile labial mask is an important tool in food handling (Video ). It can be both protracted and retracted, which is concordant with other observations in biting‐chewing mouthparts (Büsse et al, 2021b; Josten et al, 2022; Schmitt et al, 2014). Furthermore, we also analyzed lateral motion, mostly to handle the relatively large prey item as suggested earlier (Büsse et al, 2021b).…”

“…Using a graphical approach, the lateral movement of the prehensile labial mask was estimated by measuring projected angles on the videos using the program Kinovea (Joan Charmant, Bordeaux, France, General Public License). For more information on paa's we refer to Josten et al (2022).…”

“…Generally, in insects, the labium is essential in the feeding process of biting and chewing mouthparts, and it also usually protracts and retracts around a single axis (Büsse et al, 2021b; Krenn, 2019; Popham & Bevans, 1979; Schmitt et al, 2014). It is used to close the food chamber ventrally and possibly assist the maxillae in ingestion (Chapman, 1995; Josten et al, 2022; Schmitt et al, 2014). But the labium in the larvae of dragonflies and damselflies is highly modified and thus may strongly alter the resulting motions.…”

Tanning of the tarsal and mandibular cuticle in adult Anax imperator (Insecta: Odonata) during the emergence sequence

“…This structure was supposed to provide flexibility and to allow elastic energy storage (energy generated by the 0md1 adductor royalsocietypublishing.org/journal/rsfs Interface Focus 14: 20230076 muscle) and, thus, to prevent structural failure and support the masticating process [16,29,51,[89][90][91][92][93]. Furthermore, it was assumed to be used as a damper to secure the mandible against collisions with the head capsule due to large opening angles [56].…”

Mechanical and elemental characterization of ant mandibles: consequences for bite mechanics

“…Such behaviors usually generate friction between body parts and the environment and even among body parts that can lead to cuticular wear, which could also happen with the frequent use of a structure like the mandibles to process hard materials (Schofield et al 2011; Nadein and Gorb, 2021; 2022; Nadein et al, 2021; Püffel et al 2023b). Therefore, it is not surprising that substantial variation in cuticle material sclerotization levels is observed along the body of an insect (Michels & Gorb 2012; Büsse & Gorb 2018; Eshghi et al 2018; Li et al 2020; Josten et al 2022; Krings & Gorb, 2023), besides the differences among the cuticular layers or the abundance of transition or alkaline earth metals. This intraindividual variation in the cuticle can have significant functional relevance due to its effects on the cuticle material properties (Das et al 2018; Jafarpour et al 2020; Li et al 2020; Matsumura et al, 2020; Toofani et al 2020; Xing & Yang 2020; Casey et al 2022).…”