Morphological diversification has led to inter-specific variation in elastic wing deformation during flight in scarab beetles.

Y Meresman,G Ribak,R Ben-Shlomo,J F Husak

doi:10.1098/rsos.200277

Abstract

Insect wing shapes and the internal wing-vein arrangement are remarkably diverse. Although the wings lack intrinsic musculature to adjust shape actively, they elastically deform due to aerodynamic and inertial loads during flapping. In turn, the deformations alter the shape of the wing profile affecting the aerodynamic force. To determine how changes in wing-vein arrangement affect elastic wing deformation during free flight, we compared elastic wing deformations between free-flying rose chafers (Protaetia cuprea) and dung beetles (Scarabaeus puncticollis), complementing the comparison with wing static bending measurements. The broader relevance of the results to scarab beetle divergence was examined in a geometric morphometric (GM) analysis of wing-vein arrangement in 20 species differing in phylogeny and ecology. Despite rose chafers and dung beetles demonstrating similar flapping kinematics and wing size, the rose chafer wings undergo greater elastic deformation during flapping. GM analyses corrected for phylogenetic relatedness revealed that the two beetles represent extremes in wing morphology among the scarab subfamilies. Most of the differences occur at the distal leading edge and the proximal trailing edge of the wing, diversifying the flexibility of these regions, thereby changing the pattern of elastic wing deformation during flapping. Changes to local wing compliance seem to be associated with the diversification of scarab beetles to different food sources, perhaps as an adaptation to meet the demands of diverse flight styles.

Highlights

Insect wing shapes and the internal wing-vein arrangement are remarkably diverse
Tanaka et al [28] suggested that hoverfly wings would produce greater lift if they were rigid; Zhao et al [29] showed that wing flexibility reduces the generation of the aerodynamic lift; and Tobing et al [30] argued that wing flexibility reduces the production of lift but enables bumblebee wings to generate thrust
The homologies among the scarab beetle species remain very clear: the wings share similar veins, enabling a one-to-one mapping of changes in wing-vein arrangement [3,32]. Since such changes can affect the wing–air interaction, they may result in a complex interplay among flexural rigidity, flapping kinematics and fluid dynamics that confine our understanding of the aerodynamic function of flexible insect wings

Summary

Introduction

Insect wing shapes and the internal wing-vein arrangement are remarkably diverse. the wings lack intrinsic musculature to adjust shape actively, they elastically deform due to aerodynamic and inertial loads during flapping. Wing twist can compensate for the span-wise increase in the angle-of-attack (AoA) as a result of flapping, in which distal wing sections move faster than proximal sections relative to the air [11,12,13,14] It ensures lift production during both the upstrokes and downstrokes [13], distinguishing insects from flying vertebrates (reviewed by [15]). The homologies among the scarab beetle species remain very clear: the wings share similar veins, enabling a one-to-one mapping of changes in wing-vein arrangement [3,32] Since such changes can affect the wing–air interaction, they may result in a complex interplay among flexural rigidity, flapping kinematics and fluid dynamics that confine our understanding of the aerodynamic function of flexible insect wings.

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Results

Conclusion