My research focuses on the integrative biology of intraspecific variation in male Libellula pulchella dragonfly muscle physiology, flight performance, and territorial behavior. One factor that is a major contributor to this variation is infection by gregarine midgut parasites. Previous field studies demonstrate that infected males show diminished territorial behavior and mating success. I will show that infection reduces in vitro flight muscle contractile performance and lipid utilization. Both are likely contributing factors to the behavioral change observed. The reduction in flight muscle performance is strongly associated with changes in myofibrillar protein content as measured using 2D PAGE analyses. Our current working hypothesis is that some of the changes in myofibrillar protein content reflect differences in myofibrillar protein turnover rate, which is governed by the intensity of flight muscle use. I am currently testing this hypothesis by comparing calpain-like proteinase activity in healthy and parasitized flight muscles, and, in addition, by measuring in vivo flight muscle lipid utilization in individuals for which flight activity is established in the field.