Effects of Gravidity on Locust Jump Performance

Among life-history trade-offs, the cost of reproduction has been well-studied. An increase in body mass due to gravidity has been shown to negatively affect survival in vertebrates, but it has not been widely studied in invertebrates. Insects, especially American locusts (Schistocerca americana), are good models to study how life-history changes affect locomotion. For our research, we collected non-gravid and gravid female grasshoppers and conducted a five minute endurance jumping test. Non-gravid females (n=20, mean weight= 2.25 g) had an average maximum jump distance of 189 cm over the first minute. Over the five minute trial, non-gravid female jump frequency decreased by 7% and mean distance per jump decreased by 46%. In contrast, gravid females (n=12, mean weight= 2.7 g) in the first minute had an average maximum jump distance of 169 cm. Over the five minute trial, gravid female jump frequency decreased by 8% and the mean distance per jump decreased by 52%. Next, we added weights to additional groups of non-gravid and gravid females to determine how additional mass affected jump performance. The weights were either 20% or 40% of the average group body mass (n=12 for weighted non-gravid, n=8-10 for weighted gravid). During the five minute trial, jump frequency significantly decreased in weighted grasshoppers regardless of whether they were gravid or not. In addition, the mean distance per jump significantly decreased with weights in both non-gravid (p