SEASONAL AND NIGHTLY VARIATION IN GLYCOGEN RESERVES OF CALLING GRAY TREEFROGS (HYLA VERSICOLOR)

We studied seasonal and nightly variation in the trunk-muscle and liver glycogen reserves of calling male gray treefrogs (Hyla versicolor) during three breeding seasons in Connecticut. The objectives of the study were to (1) determine whether glycogen reserves decline throughout the course of the breeding season, (2) measure the rate of glycogen depletion in calling males on individual nights and use this to estimate the relative importance of glycogen and lipid reserves for call production, and (3) determine whether the length of calls given by males affects the rate of glycogen depletion. Glycogen reserves measured early in the evening declined during the 1988 breeding season, a dry year when feeding may have been difficult, but not in 1991, a wetter year when most males were able to feed. Trunk-muscle glycogen reserves declined by 50-60% after two hours of calling. Glycogen reserves supply only about 25% of the energy needed for an evening of call production, with the remainder presumably coming from much larger lipid reserves in the trunk muscles themselves. The rate of glycogen depletion was not affected by call duration.