The Anatomical Record

Roze, Malo; Gorb, Stanislav N.; Zeimet, Timo; Krings, Wencke

doi: 10.1002/ar.25602pmid: 39511980

Insects process their food with their cuticle‐based mouthparts. These feeding structures reflect their diversity and can, in some cases, showcase adaptations in material composition, mechanical properties, and shape to suit their specific dietary preferences. To pave the way to deeply understand the interaction between mouthparts and food and to determine potential adaptations of the structures to the food, this study focuses on the mandibles of two praying mantis species. Gongylus gongylodes feeds mainly on Diptera, and Sphodromantis lineola forages on larger prey. Employing scanning electron microscopy, the mandibular morphologies were analyzed. The degree of the cuticle tanning was tested using confocal laser scanning microscopy. Furthermore, the contents of transition and alkaline earth metals in the mandible cuticle were studied using energy‐dispersive X‐ray spectroscopy and the mechanical properties tested by nanoindentation. We found that S. lineola mandibles show pronounced gradients of Young's modulus and hardness from the basis to the tip, which might be an adaptation against high stresses during biting and chewing. G. gongylodes, in contrast, did not show pronounced gradients, which may indicate that there is less stress involved in feeding—necessary to test in future studies. The mechanical properties of manidibles in both species are related to the degree of cuticle tanning but also positively correlate with the content of magnesium. These findings enrich our understanding of insect cuticle biology but also present new sets of data on praying mantis structures.

Ito, Kai; Kubo, Mugino O.; Kodera, Ryo; Takeda, Sei‐ichiro; Endo, Hideki

doi: 10.1002/ar.25599pmid: 39588911

Masticatory muscles are composed of the temporalis, masseter, and pterygoid muscles in mammals. Each muscle has a different origin on the skull and insertion on the mandible; thus, all masticatory muscles contract in different directions. Collecting in vivo data and directly measuring the masticatory muscles anatomically in various Carnivora species is practically problematic. This is because some carnivorans can be ferocious, rare, or even extinct. Consequently, the most practical method to collect data on the force generated by the masticatory muscle is to estimate the force based on skulls. The physiological cross‐sectional area (PCSA) of each masticatory muscle, which correlates to the maximum force that can be produced by a muscle, was quantified. Using computed tomography, we defined the three‐dimensional measurement area for 32 carnivoran species based on the origin and insertion of masticatory muscles specified by observable crests, ridges, and scars. Subsequent allometric analysis relating the measurement area on skull surface to the PCSA for each masticatory muscle measured in fresh specimens revealed a strong correlation between the two variables. This finding indicates that within Carnivora, an estimation of absolute masticatory muscle PCSA can be derived from measurements area on skull surface. This method allows for the use of cranial specimens, housed in museums and research institutions, that lack preserved masticatory muscles in quantitative studies involving masticatory muscle PCSA. This approach facilitates comprehensive discussions on the masticatory muscle morphology of Carnivora, including rare and extinct species.