title: Mechanoreceptor distribution in stag beetle jaws corresponds to the material stress in fights.
abstract: Male stag beetles (Lucanidae) use their extremely elongated jaws to pinch their rivals forcefully in male-male battles. The morphology of these jaws has to be a compromise between robustness (to withstand the bite forces), length and weight. Cyclommatus metallifer stag beetles circumvent this trade-off by reducing their bite force when biting with their slender jaw tips. Here we describe the functional mechanism behind the force modulation behaviour. Scanning Electron Microscopy and micro CT imaging show large numbers of small sensors in the jaw cuticle. We find a strong correlation between the distribution of these sensors and that of the material stress in the same jaw region during biting. The jaw sensors are mechanoreceptors with a small protrusion that barely protrudes above the undulating jaw surface. The sensors stimulate dendrites that extend from the neuronal cell body through the entire thickness of the jaw exoskeleton towards the sensors at the external surface. They form a sensory field that functions in a feedback mechanism to control the bite muscle force. This negative feedback mechanism enabled the stag beetles to evolve massive bite muscles without risking overloading their valuable jaws.
authors.affiliation: University of Antwerp, Laboratory of Functional Morphology, Universiteitsplein 1, B-2610 Antwerpen, Belgium; University of Antwerp, Laboratory of Biophysics and BioMedical Physics, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium. Electronic address: jana.goyens@uantwerpen.be.
authors.forename: J
authors.initials: J
authors.lastname: Goyens
authors.affiliation: University of Antwerp, Laboratory of Biophysics and BioMedical Physics, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Dirckx
authors.affiliation: University of Antwerp, Laboratory of Functional Morphology, Universiteitsplein 1, B-2610 Antwerpen, Belgium; Department of Movement and Sport Sciences, Ghent University, 9000 Ghent, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Aerts
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001517:Coleoptera / Q000502:physiology* / Q000648:ultrastructure*; D056228:Feedback, Sensory; D008297:Male; D008465:Mechanoreceptors / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D055114:X-Ray Microtomography
keywords: Animal weapon; Cyclommatus metallifer; Lucanidae; Mechanical stress; Sensory field; Sexual selection