Energetics of calling and metabolic substrate use during prolonged exercise in the European treefrog Hyla arborea

Rates of oxygen consumption and carbon dioxide release were measured in calling and resting European tree frogs using open-flow-through respirometry. The energetic cost of calling was high with an average of 1.076 ml O2/(g.h) at average call rates of 8,000 calls/h. The maximum factorial metabolic scopes averaged 24 with momentary peak values ranging between 5 and 41. There was a threefold difference in O2-consumption between individual males calling at the same rate. Respiratory quotients indicated that both lipids and carbohydrates were used to fuel calling. Carbohydrates provided the major fuel (69% on average) with dependence on carbohydrates increasing with call rate. In contrast to marathon runners, there was no shift in metabolic substrate use over a calling period of 2-3 h.