Effects of Oxygen on Jump Performance and Lactate Production in the American Locust

Insects are the most evolutionarily successful animals in part due to their air-filled tracheal respiratory system. The tracheal system plays a key role in oxygen consumption and consists of an intricate network of tubes that exchange gases between the atmosphere and tissues (Greenlee et. al, 2009). Some insects, including grasshoppers, also have air sacs that allow for enhanced conductive airflow (Greenlee et. al, 2009). During the intermolt periods, the American locust (Schistocerca americana) does not increase muscle mass but doubles their body mass, which compresses the tracheae. In a recent study, late-stage grasshoppers had a reduced air sac ventilation frequency, decreased convective capabilities, and had less of their body dedicated to their respiratory system (Kirkton et. al 2012). All of these factors hinder both their oxygen delivery capacity and jump performance. We forced force early-stage (day 2) and late-stage (day 8) 6th instar grasshoppers to jump in artificial oxygen atmospheres (5%, 10%, 21%, 35% oxygen) and predicted that if oxygen delivery is compromised then late-stage grasshopper jumping performance would correlate with oxygen level. We used a minimum of n=10 early and late-stage 6th instar grasshoppers per oxygen treatment (total of 80-100 grasshoppers). Grasshoppers were individually placed in a previously constructed chamber and aggressively stimulated by paintbrushes to jump for five minutes. Jumps per minute were recorded and immediately following the five-minute jump period, grasshoppers were frozen in liquid nitrogen to later analyze lactate production and HIF protein expression. Our initial results show that oxygen levels affect late-stage grasshoppers more than early-stage grasshoppers during repeated jumping. At 5% oxygen, late-stage grasshoppers jumped significantly less than the early-stage grasshoppers over the five-minute jump period. At 10% oxygen, similar trends were observed. At 21% oxygen, there were no consistent differences in jump performance. At 40% oxygen, early-stage grasshoppers jumped significantly less over the five-minute jump period than late-stage grasshoppers. Our initial results suggest that jump performance is impacted by age and oxygen levels. We are in the process of relating jump performance of the grasshoppers in different oxygen concentrations to resulting biochemical and molecular processes in the jumping muscles. We are currently measuring HIF protein expression and lactate production using the same animals that we jumped. If late-stage grasshoppers show reduced jumping performance and increased lactateproduction at lower oxygen levels, we predict increased HIF protein expression as well.