Immune Function, Body Size, and Parasite Load in Lubber Grasshoppers

Immunity is an important biological property of organisms that protects them from parasites. Similarly, body size is one of the most important biological traits because almost all biological processes, from the cellular to the ecosystem level, scale with body size. Our goal was to determine the correlation between body size and immune function in different populations of the eastern lubber grasshopper (Romalea microptera) which differ in body size. Field data was collected on grasshopper location, size (thorax and femur lengths), and immune function (measured by melanization response). In accordance with previous work, we found a significant body size cline among populations of south Florida grasshoppers: on average, small adult grasshoppers are found in western populations whereas large grasshoppers are found in eastern populations. However, we did not find a significant relationship between body size and one measure of immune function, either within or across these populations. Future work should be directed at understanding when body size and immune function might or might not be correlated.