Energetics of vocalization by an anuran amphibian (Hyla versicolor)

SummaryThe metabolic demands of vocalization byHyla versicolor were determined by measuring oxygen consumption and whole body lactate content of calling animals. A stepwise multiple regression analysis identified both calling rate (calls/h) and call duration (s/call) as significant determinants of oxygen consumption during calling. These two variables accounted for 84% of the total variation in oxygen consumption observed in calling frogs. Aerobic metabolism $$\left( {\dot V_{O_2 } {\text{call}}} \right)$$ increased linearly with calling rate and call duration, reaching a peak value of 1.7 ml O2/(g·h) at the highest vocalization effort. For comparison, metabolic rates of the same individuals were also measured during short bouts of vigorous locomotor exercise $$\left( {\dot V_{O_2 } {\text{ex}}} \right)$$ induced by mechanical stimulation. The mean value of $$\dot V_{O_2 } {\text{ex}}$$ was only 62% of the peak $$\dot V_{O_2 } {\text{call}}$$ , and 5 of 13 frogs had rates of oxygen consumption during calling that exceeded their $$\dot V_{O_2 } {\text{ex}}$$ . Whole body lactate levels were measured in two samples of calling frogs, one collected early in the evening (2100–2115 h) and the other 1.5 h later (2230–2245 h). The frogs in the second sample had significantly lower lactate levels (0.10 mg/g) than the frogs collected early in the evening (0.22 mg/g). Hence, vocalization does not entail the use of anaerobic metabolism, although lactate levels may be slightly elevated at the onset of an evening of calling. Calling rates of unrestrained frogs in a large chorus were measured at regular intervals during an evening. During the first half hour of calling, rates increased gradually from an initial mean value of 600 calls/h at 2030 h to nearly 1400 calls/h at 2100 h. These data indicate that acoustic advertisement byHyla versicolor is among the most energetically expensive activities regularly undertaken by any anuran, and indeed, is the most demanding yet measured in an ectothermic vertebrate.