Do female frogs have higher resting metabolic rates than males? A case study withXenopus allofraseri

The energetic costs of body maintenance can have a profound influence on the energy that an individual can allocate to other functions such as growth, locomotion, or reproduction. Therefore, resting metabolism can ultimately affect an individual's survival or reproductive success, especially when food is limited. Although males and females often differ in their body composition (e.g. sex organs and fat accumulation) and body size, the occurrence and direction of sexual dimorphism in resting metabolism remains poorly understood in anurans. In the present study, we investigated whether males and females of the false Fraser's clawed frogXenopus allofraseridiffer in their resting metabolic rates. We used an open-flow push-through respirometry system to measure the volume of carbon dioxide (VCO2) produced by animals at rest. Variation inVCO2minwas explained by ambient temperature, body size, and sex. For a similar body size, our results revealed that females had about a 50% higher resting metabolic rate (RMR) than males. We suggest that the enhanced investment in gamete production in females compared to males may explain this difference. We further suggest that a lower RMR in males compared to females at similar body size could be selectively advantageous as unallocated energy may be devoted to costly mating, in support of the 'compensation' hypothesis.