Micro‐CT measured tracheal changes in the metathoracic femur of developing American locusts

Abstract

In support of the hypothesis that larger insects have more oxygen delivery problems, older/larger grasshoppers have more abdominal respiratory structures. However, it is unclear if they also have more femoral respiratory structures because the anaerobic capacity of the jumping muscle increases during development. Disarticulated adult and juvenile femurs were dried overnight and placed individually in the scanning chamber of a SkyScan 1074 micro‐computed tomography unit. Images were reconstructed into transverse cross sections using computer software. Transverse sections at “stations” 20% (closest to the thorax), 40% and 60% (closest to the knee) of the length along each femur were analyzed. Near the thorax, the adult femur has three dorsal tracheae, a pair of ventral tracheae and a medial trachea. The adult dorsosagittal and dorsomedial tracheae merge at the 30% station; the ventral tracheae merge and the medial trachea vanishes at the 50% station. Near the thorax, the juvenile femur includes a single central trachea. We found tracheae void fractions to increase about 50% along the adult femur and to decrease about 50% along the juvenile femur. Void fractions were similar between adult and juvenile at the 40% station. These results suggest that older/larger grasshoppers have proportionally more respiratory structures in the distal portion of the jumping leg. Supported in part by NSF DUE 0511287 (AJR).