Using corrosion casts to understand oxygen delivery in the grasshopper leg

Abstract

The light‐weight, air‐filled tracheal system has allowed insects to be the most evolutionary successful animals on the planet. Oxygen enters through spiracular openings before passing down tracheal tubes that branch into successively smaller tubes that eventually become tracheoles, which serve as the site of gas exchange. Depending on the species and life history stage, oxygen delivery down the tracheae may occur via diffusion, convection, or both. While adult Schistocerca americana grasshoppers use abdominal pumping and convection to drive oxygen through their head, thorax, and abdomen, it is less clear how oxygen delivery occurs down the metathoracic leg. We cannulated the tracheal system of an adult grasshopper and injected a low viscosity resin under vacuum, to create a corrosion cast of the major tracheal branches of the metathoracic leg. After the low viscosity resin had solidified, grasshopper tissue was digested leaving only the tracheal cast. Using light microscopy, we measured the radii of the main tracheae and their subsequent branches. These tracheal dimensions followed Murray's Law, suggesting that the network provided convective oxygen delivery. We will examine the casts using scanning electron microscopy to visualize tracheal branching patterns and estimate oxygen flow patterns throughout the metathoracic leg. This research has been supported by funding from Union College.