Ecophysiology of Osmotic Stress Tolerance in the African Clawed Frog (Xenopus laevis) and Amietophrynus regularis Under Simulated Drought Conditions

This study investigates osmotic stress physiology and drought tolerance mechanisms in Xenopus laevis and the African common toad Amietophrynus regularis under controlled simulated drought conditions, in the context of increasing drought frequency in the guinea savanna zone of North Central Nigeria. Both species are common in the savanna-forest transition of Plateau and Nassarawa States but face increasing exposure to dry-season water stress, yet their comparative osmoregulatory physiology under Nigerian conditions is uncharacterised. Juveniles and adults of both species were subjected to controlled dehydration experiments at 28 and 32 degrees Celsius. Body mass, plasma osmolality, urine concentration, muscle water content, haematocrit, and nitrogenous waste excretion were monitored at regular intervals. Recovery rates from dehydration were also assessed. Amietophrynus regularis tolerated water losses of up to 38 percent body mass before showing mortality, compared to 28 percent in Xenopus. At elevated temperature, survival time was reduced by 34 percent in both species. Plasma osmolality reached 480 mOsm/kg in Amietophrynus regularis at 30 percent dehydration, activating urea-based osmotic retention. Xenopus showed earlier onset of muscle damage at equivalent dehydration levels. The study fills a critical gap in the ecophysiology of Nigerian amphibians and provides a physiological basis for predicting the vulnerability of both species to projected climate change impacts in the North Central zone. Keywords: osmotic stress, amphibian physiology, drought tolerance, Amietophrynus regularis, Xenopus laevis.