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

Abstract

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 frog Xenopus allofraseri differ in their resting metabolic rates. We used an open-flow pushthrough respirometry system to measure the volume of carbon dioxide (VCO 2) produced by animals at rest. Variation in VCO 2min was 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.

Morphometrics of Xenopus laevis Kept as Laboratory Animals

“…Whether the latter assumption holds true for a captive setting under standardized conditions seems questionable. In addition to the dimorphism, as seen in the measurements, there is evidence that in anurans, specifically Xenopus allofraseri , females have a higher basal metabolic rate [ 39 ]. For both reasons, female and male frogs´ body conditions cannot be evaluated with one set of data.…”

Ecogeographical Adaptation Revisited: Morphological Variations in the Plateau Brown Frog along an Elevation Gradient on the Qinghai–Tibetan Plateau

“…With the significant relationship between SVL and primary productivity ( Table 2 ), the unresponsive body size along elevation may be restricted by the lower food availability at a higher elevation [ 28 , 30 ]. Even though we suggest that more resources were allocated to body growth than to extremities, female frogs are found to have a higher resource requirement in body maintenance [ 65 ]. Moreover, there was sampling bias towards males in this study, and the female sample size was small at a lower elevation ( Supplementary Materials Table S2 ).…”

“…The strong and positive association between morphological development and NDVI ( Table 2 ) was consistent with the primary productivity hypothesis [ 28 ], which implies that body size must be sustained by an adequate food supply and predicts larger body sizes in more productive areas [ 28 , 30 ]. With reference to the restraining effect of temperature detected by hierarchical partitioning ( Table 2 ), it can be explained by the temperature–size rule that refers to a decrease in adult body size by early maturity through increasing growth rate and development under high temperatures [ 65 ]. For precipitation, our results showed a positive link with growth that is contrary to the prediction from the water availability hypothesis [ 9 ].…”

“…In more detail, the positive influence of precipitation brought by the rainwater might exert a catalytic force on vegetation growth (primary productivity) and give rise to the biomass of the habitat [ 68 , 69 ]. Thermally, it could also alleviate desiccation and temperature, which leads to a beneficial delay in growth rate as discussed [ 65 ]. Moreover, the importance and contribution of the biological and environmental variables vary greatly between male and female R. kukurnoris ( Table 2 ).…”

The interaction between metabolic rate, habitat choice, and resource use in a polymorphic freshwater species

“…These environments also elicit changes in morphology and activity and correspond with differences in diet, suggesting that some of the same drivers may cause the differences in metabolic rates (Olsson & Eklöv, 2005 ). Metabolic rates can also differ between sexes (Ducret et al, 2020 ; Ladds et al, 2017 ; Madenjian, 2011 ). For example, males with costly secondary sexual characteristics or high activity rates, which are both subject to strong selection pressure, often have higher metabolic rates than females (Henderson et al, 2003 ; Makiguchi et al, 2017 ; Somjee et al, 2018 ).…”