3D Morphometrics of Lucanus cervus cervus (Linnaeus, 1758) (Coleoptera: Lucanidae)

The European stag beetle Lucanus cervus cervus is the largest European member of the Lucanidae and is characterised by the extremely enlarged mandibles of the male. Some aspects of the morphology of this species have been extremely well studied, while others have been largely neglected. In the present paper we fill some of these gaps by focusing on 3D measurements based on a µ-CT scan. We show that the largest part of the body is filled by a massive tracheal system (48.8%), followed by the exoskeleton (21.1%). The massive tracheal system covers large parts of the internal anatomy, leaving limited space for other systems such as the nervous system (0.2%) or the digestive system (0.7%), which are very small and delicate compared to other species. We suggest that no significant relative increase in the volume of the tracheal system is possible in a flying insect without potentially rendering another organ system inoperable. The cuticle of L. cercus cercus is extremely thick compared to other species, which is most likely due to the fact that the males have extremely enlarged mandibles, which are also used in male-male fights. They can generate strong forces that also result in massive stresses that need to be dissipated by the thick cuticle. We can also show that there are significant differences between 2D and 3D measures of specific distances in highly 3-dimensional structures such as the length of the mandibles. We therefore suggest that such 3D measures be included in future analyses. In summary, we hope to further promote the importance and significance of 3D morphometric measures and suggest that at least the volumes of the studied materials should be included in future CT-based studies of insects.