Form–function relationships in dragonfly mandibles under an evolutionary perspective

Abstract

Functional requirements may constrain phenotypic diversification or foster it. For insect mouthparts, the quantification of the relationship between shape and function in an evolutionary framework remained largely unexplored. Here, the question of a functional influence on phenotypic diversification for dragonfly mandibles is assessed with a large-scale biomechanical analysis covering nearly all anisopteran families, using finite element analysis in combination with geometric morphometrics. A constraining effect of phylogeny could be found for shape, the mandibular mechanical advantage (MA), and certain mechanical joint parameters, while stresses and strains, the majority of joint parameters and size are influenced by shared ancestry. Furthermore, joint mechanics are correlated with neither strain nor mandibular MA and size effects have virtually play no role for shape or mechanical variation. The presence of mandibular strengthening ridges shows no phylogenetic signal except for one ridge peculiar to Libelluloidea, and ridge presence is also not correlated with each other. The results suggest that functional traits are more variable at this taxonomic level and that they are not influenced by shared ancestry. At the same time, the results contradict the widespread idea that mandibular morphology mainly reflects functional demands at least at this taxonomic level. The varying functional factors rather lead to the same mandibular performance as expressed by the MA, which suggests a many-to-one mapping of the investigated parameters onto the same narrow mandibular performance space.

Material composition of the mouthpart cuticle in a damselfly larva (Insecta: Odonata) and its biomechanical significance

“…The mandibles ( figure 3 ) are used to crush the prey's outer body wall; they are sturdy and produce high biting forces [ 19 , 30 ]. The mobility of the mandibles is restricted to one axis by the mandibular articulations [ 20 , 29 , 31 ]. The material composition found in this area, i.e.…”

Strong biomechanical relationships bias the tempo and mode of morphological evolution

“…Simply demonstrating many-to-one mapping in biomechanical systems is likely to miss a rich suite of evolutionary and mechanical dynamics that shape diversification ( Figure 4 ). By considering the tempo and mode of evolution, generalizable interactions between mechanics and diversification are likely to emerge ( Scales and Butler, 2016 ; Blanke et al, 2017 ). Evolutionary studies of many-to-one mapping have flourished in recent years, with particular focus on how natural selection and developmental constraints impact the evolution of complex mechanical systems in the wild (e.g.…”

A biomechanical analysis of prognathous and orthognathous insect head capsules: evidence for a many‐to‐one mapping of form to function

“…To prevent free body motion due to rounding errors in the solution phase, three separate nodes at the occipital foramen were also constrained in all directions. Material properties (Young's moduli) of parts of the head capsule (clypeus and anterior tentorial arms) and eyes were measured for the dragonfly by nano‐indentation under wet conditions using established routines (Oliver & Pharr, ; Klocke & Schmitz, ; Blanke et al ., ) (Data S1). A Poisson's ratio of 0.3 was assumed for all materials based on studies of lobster cuticle (Fabritius et al ., ; Nikolov et al ., ).…”