The metabolic cost of amplexus in the grey tree frog (Hyla versicolor): assessing the energetics of male mating success

Abstract

The metabolic cost of amplexus was calculated for 37 pairs of grey tree frogs, Hyla versicolor, by measuring the rate of O2consumption of each amplexed pair and the combined resting rates of O2consumption of the two individuals of each pair, and calculating the difference. The mean cost of amplexus was 1.20 mL O2·h–1for each pair. The cost of amplexus was correlated with the mass of the males but not the mass of the females, and amplexus with artificial males did not have a significant effect on female metabolic rate. Therefore, the cost of amplexus appears to be incurred entirely by the male. Reproductively successful males spend less time calling per evening than reproductively unsuccessful males, leaving the chorus early to enter into amplexus. The mass-specific cost of amplexus (0.158 mL O2·g–1·h–1) is approximately 1/10 the mass-specific cost of call production (1.620 mL O2·g–1·h–1), and net energy consumption per evening is less for reproductively successful male H. versicolor than it is for reproductively unsuccessful males. The probability of future reproductive success is enhanced if reproductive success is energetically less expensive than reproductive failure.