The negative effects of gravidity on locomotion have been well documented in terrestrial vertebrates but are relatively unknown in insects. During gravidity, the egg mass of Schistocerca americana grasshoppers can be up to 40% of their body mass. However, jumping muscle mass remains relatively unchanged during gravidity. Using female grasshoppers that ranged in body size from 1.6 g to 3.3 g (n=25), we investigated how gravidity affects maximal jump performance. Each grasshopper’s maximal jump was captured using eight Qualisys infrared high-speed cameras filming at 1121 fps. Biomechanical data were generated using Qualisys Track Manager and the effects of body size/gravity were analyzed using regression in JMP. Larger grasshoppers have significantly more eggs, a larger egg mass, and a greater portion of their body dedicated to eggs (egg mass: y=0.52x-0.82; r2=0.76; p<0.0001). We found that the take off angle, take off acceleration, force, and time spent in the air during a jump was similar regardless of body size or gravidity. However, larger, more gravid grasshoppers had significantly lower take off velocities (y=-0.40x+4.36; r2=0.22; p<0.02) and did not jump as far (y=-0.18x+1.44; r2=0.18; p<0.05). When we compared the actual jump distance to the predicted jump range, we found that more gravid grasshoppers were significantly closer to the expected range than smaller, less gravid grasshoppers (y=6.23x+77.31; r2=0.16; p<0.05). In addition, more gravid grasshoppers produced significantly more energy during a jump than less gravid animals (y=2.94x+5.77; r2=0.19; p<0.05). The increased jump energy of more gravid grasshoppers may be due to an increased reliance on anaerobic ATP production. This supports previous work that gravid grasshoppers have more problems with oxygen delivery. For example, gravidity reduces the total tracheal respiratory volume by 10%, reduces tidal volumes, and increases respiratory rates. Future work will measure phospho-arginine and lactate to determine, if due to oxygen delivery problems, gravid grasshoppers rely more on anaerobic ATP to produce powerful escape jumps.
This research was supported by NSF Award 1827495 to SDK.