During ovigerous cycles, female locusts (Schistocerca americana) undergo a weight gain of up to 40% of their total body mass. However, previous research has shown that gravid female locusts continue to achieve similar jump height and distance during their pre-gravid and inter-gravid conditions, indicating female locusts might have intrinsic means to modulate the neuromechanics of their jumping legs in response to increases in weight. This prediction contradicts the current understanding of the degree to which locusts can control their escape jumping movements, which are understood to be a fixed all-or-nothing output. We hypothesized that female locusts modulate the contraction time in their femur extensor muscles to augment the power achieved by their jumping legs during conditions of artificial weight gain. We also hypothesized that this degree of control is not performed in male locusts since they do not naturally experience substantial changes in body mass throughout their adult reproductive stage.
Locusts were recorded using simultaneous high-speed video capture (1500 frames per second) and bilateral electromyogram (EMG) recordings during evoked escape jumps. Multiple jumps were recorded for each individual, corresponding to different weight gain conditions. The locusts were mounted with an apparatus to hold clay beads representing a range of masses that would increase body weight by 20-50% of their total body mass. The peak angular velocity and acceleration of the jumping legs were calculated using position tracking software (DeepLabCut) and subsequent kinematic analysis of the leg rotation using custom scripts in R. Contraction time was calculated from the femoral extensor muscle EMG recordings. In comparing male and female locusts, contraction time was plotted as a function of angular velocity and acceleration to demonstrate the relationship between body mass and jump performance. These results parallel ongoing work investigating the relationship between decreased tidal volumes and jumping performance in female locusts and compensation mechanisms related to overcoming these physiological limitations.