Abstract

Derived from the respiratory tracheae, bush-crickets’ acoustic tracheae (or ear canal) are hollow tubes evolved to transmit sounds from the external environment to the interior ear. Due to the location of the ears in the forelegs, the acoustic trachea serves as a structural element that can withstand large stresses during locomotion. In this study, we report a new Atomic Force Microscopy Force Spectroscopy (AFM-FS) approach to quantify the mechanics of taenidia in the bush-cricket Mecopoda elongata. Mechanical properties were examined over the longitudinal axis of hydrated taenidia, by indenting single fibres using precision hyperbolic tips. Analysis of the force-displacement (F-d) extension curves at low strains using the Hertzian contact model showed an Elastic modulus distribution between 13.9 MPa to 26.5 GPa, with a mean of 5.2 ± 7 GPa and median 1.03 GPa. Although chitin is the primary component of stiffness, variation of elasticity in the nanoscale suggests that resilin significantly affects the mechanical properties of single taenidia fibres (38% of total data). For indentations up to 400 nm, an intricate chitin-resilin response was observed, suggesting structural optimization between compliance and rigidity. Finite-element analysis on composite models demonstrated that the Elastic modulus is sensitive to the percentage of resilin and chitin content, their location and structural configuration. Based on our results, we propose that the distinct moduli of taenidia fibres indicate sophisticated evolution with elasticity playing a key role in optimization.