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

We studied seasonal and nightly variation in the trunk-muscle and live r glycogen reserves of calling male gray treefrogs (Hyla versicolor) d uring three breeding seasons in Connecticut. The objectives of the stu dy were to (1) determine whether glycogen reserves decline throughout the course of the breeding season, (2) measure the rate of glycogen de pletion in calling males on individual nights and use this to estimate the relative importance of glycogen and lipid reserves for call produ ction, and (3) determine whether the length of calls given by males af fects the rate of glycogen depletion. Glycogen reserves measured early in the evening declined during the 1988 breeding season, a dry year w hen feeding may have been difficult, but not in 1991, a wetter year wh en most males were able to feed. Trunk-muscle glycogen reserves declin ed by 50-60% after two hours of calling. Glycogen reserves supply only about 25% of the energy needed for an evening of call production, wit h the remainder presumably coming from much larger lipid reserves in t he trunk muscles themselves. The rate of glycogen depletion was not af fected by call duration.