The management of metabolic energy storage during the life cycle of mayflies: a comparative field investigation of the collector-gatherer Ephemera danica and the scraper Rhithrogena semicolorata.

The concentration and seasonal dynamics of the major energy storage components, triglycerides and glycogen, were measured in two species of mayfly (Rhithrogena semicolorata and Ephemera danica) with contrasting life cycle strategies living in a small mountain stream. E. danica is a burrowing, semivoltine collector-gatherer; R. semicolorata is univoltine and scrapes periphyton from stones. This is the first publication which focuses on the role of metabolic energy sources during the larval life span of two mayfly species until the larvae emerge. Although triglycerides are the major energy reserve in both species (>84% of total energy storage) throughout the whole larval development their seasonal dynamic differed considerably. In R. semicolorata the triglyceride concentration declined during the last weeks prior to emergence in both sexes. The same pattern was found in female larvae of E. danica, but not in male E. danica. It is suggested that females use triglycerides in the last larval stages for egg maturation, which is completed in the last larval instar. In male E. danica the triglyceride concentrations remained high until emergence, presumably due to their high energy demands as adults for their swarming flights. Glycogen concentrations did not show such a difference between species and sexes. Its significance as a storage substrate for energy is rather low; however, concentrations decreased in both species and sexes prior to emergence.