The jaws of different species of stag beetles show a large variety of shapes and sizes. The male jaws are used as weapons in fights, and they may exert a very forceful bite in some species. We investigated in 16 species whether and how the forcefulness of their bite is reflected in their jaw morphology. We found a large range of maximal muscle forces (1.8–33 N; factor of 18). Species investing in large bite muscles also have disproportionately large jaw volumes. They use this additional jaw volume to elongate their jaws, increasing their chances of winning in battles. The fact that this also decreases the mechanical advantage is largely compensated for by elongated in-levers. As a result, high muscle forces are correlated with elevated bite forces (0.27–7.6 N; factor of 28). Despite the large difference in the forcefulness of their bite, all investigated species experience similar Von Mises stresses in their jaws while biting (29–114 MPa; factor of 4.0; calculated with finite element simulations). Hence, stag beetles have successfully adapted their jaw anatomy according to their bite force in fights.
The authors declare no competing or financial interests.
J.G. executed the micro-CT scans of the male specimens, ran the FE simulations and drafted the article. J.G., J.D. and P.A. analysed and interpreted the findings and revised the article.
This study was supported by a Bijzonder Onderzoeksfonds grant (IDBOFUA 2011-445-a) of the Research Council of the University of Antwerp. The SkyScan1172 high-resolution micro-CT scanner, located at the VUB facilities, was funded by the Hercules Foundation (Herculesstichting, grant no. UABR/ 11/004).
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.141614.supplemental
- Received April 7, 2016.
- Accepted July 15, 2016.
- © 2016. Published by The Company of Biologists Ltd