Gravidity Impacts Respiratory Function, Tracheal Volume, and Jump Performance in Grasshoppers

Abstract

The negative effects of gravidity on respiration and locomotion have been well documented in terrestrial vertebrates but is relatively unknown in insects. During gravidity, the egg mass of Schistocerca americanagrasshoppers can be up to 40% of their body mass. We investigated whether this increase in egg mass impacted oxygen delivery, jump performance, and anaerobic metabolism. Using micro‐dissections and live video analysis, we examined the tracheal system of thirty‐six female grasshoppers across a range of body masses. We found that larger grasshoppers had significantly more eggs, a larger egg mass, and a greater portion of their body dedicated to eggs. In addition, abdominal compressibility (tidal volume) significantly decreased with gravidity. However, there was a significant positive correlation between gravidity and abdominal compression rate, suggesting that gravid grasshoppers make up for smaller tidal volumes by increasing respiratory rate. Furthermore, abdominal compression rates correlated with the inflation of proximal and distal femoral air sacs suggesting a direct impact on oxygen delivery to the jumping muscle. Using microCT analysis, the percent of tracheal volume in the grasshoppers significantly decreased with gravidity (23.6% in nongravid to 13.8% in gravid). During five‐minutes of repeated jumping, gravid grasshoppers had a significantly 30% lower jump rate. However, the average distance per jump did not vary with gravidity. There was no significant effect of gravidity on muscle lactate measured after five minutes of jumping. However, muscle lactate was positively correlated with total distance jumped during the five minutes, which was significantly higher in nongravid grasshoppers. In conclusion, gravidity lowered tracheal volumes, altered ventilatory mechanisms, and reduced jump performance.