Meeting Abstract
Insects breathe using a complex network of rhythmically collapsing tracheal tubes, facilitating active ventilation. In some insects, including Zophobas morio, the tracheae collapse in an uneven pock-mark like pattern, but not all collapse patterns are identical, nor do tracheae collapse at the same hemolymph pressures. The softer semi-chitinous walls of tracheae are reinforced with rings of taenidia, made primarily of stiffer sclerotized chitin fiber bundles, possibly providing a materials-based explanation for varying compression patterns. Teanedia also vary in branching, width, and orientation. Here we ask, do the tracheae vary in Young’s modulus along their lengths? We also compare these changes between the individual components of the tubes. We hypothesize that the teanedia will have higher Young’s modulus and variance than the intertaenidial portions of the trachea, contributing to significant variability in tracheal stiffness. To quantify variation in Young’s modulus, we used atomic force microscopy (AFM) to measure local Young’s moduli at regular intervals along the length of the tubes. Sections of tracheae were excised from the left dorsal meso-thoracic tracheal trunks in 7 darkling beetles. We found that the Young’s modulus measurements clustered bimodally between lower (0.44±0.04 GPa) and higher values (4.92±3.41 GPa) in the data sets analyzed (n = 4). The lower values, which may be the softer basal layer of the tracheae, are relatively constant while the higher values, which may be the stiffer teanedia, vary much more (1.73-10.67 GPa). As a composite material, varying the stiffness of the reinforcing teanedial fibers can change the effective stiffness of the tracheae more efficiently than changing all the individual components’ stiffness independently to achieve the same variation. Supported by NSF 1558052 and 1301037
