The role of ambient temperature and body mass on body temperature, standard metabolic rate and evaporative water loss in southern African anurans of different habitat specialisation

Temperature and water availability are two of the most important variables affecting all aspects of an anuran’s key physiological processes such as body temperature (T(b)), evaporative water loss (EWL) and standard metabolic rate (SMR). Since anurans display pronounced sexual dimorphism, evidence suggests that these processes are further influenced by other factors such as vapour pressure deficit (VPD), sex and body mass (M(b)). However, a limited number of studies have tested the generality of these results across a wide range of ecologically relevant ambient temperatures (T(a)), while taking habitat use into account. Thus, the aim of this study was to investigate the role of T(a) on T(b), whole-animal EWL and whole-animal SMR in three wild caught African anuran species with different ecological specialisations: the principally aquatic African clawed frog (Xenopus laevis), stream-breeding common river frog (Amietia delalandii), and the largely terrestrial raucous toad (Sclerophrys capensis). Experiments were conducted at a range of test temperatures (5–35 °C, at 5 °C increments). We found that VPD better predicted rates of EWL than T(a) in two of the three species considered. Moreover, we found that T(b), whole-animal EWL and whole-animal SMR increased with increasing T(a), while T(b) increased with increasing M(b) in A. delalandii and S. capensis but not in X. laevis. Whole-animal SMR increased with increasing M(b) in S. capensis only. We did not find any significant effect of VPD, M(b) or sex on whole-animal EWL within species. Lastly, M(b) did not influence T(b), whole-animal SMR and EWL in the principally aquatic X. laevis. These results suggest that M(b) may not have the same effect on key physiological variables, and that the influence of M(b) may also depend on the species ecological specialisation. Thus, the generality of M(b) as an important factor should be taken in the context of both physiology and species habitat specialisation.