African clawed frog

The African clawed frog (Xenopus laevis) is native to southern Africa where they live a scavenging lifestyle in ponds, swamps and calm streams. The flattened bodies and powerful webbed hind limbs of these frogs are designed for swimming and an almost fully aquatic existence whereas the delicate digits of their forelimbs help to direct food to their mouth. However, during the dry season, water levels can fall to critical levels, leaving the frogs with two options for survival. Nocturnal migration is usually the first choice, the frogs move to seek bigger ponds, but they are not well designed for moving on land. If migration is not possible, they dig into the soft mud of the drying pond using clawed hind feet and enter a resting state of estivation. Estivation allows the animals to survive the inhospitable dry environment and wait for more desirable conditions to recur and facilitate a return to an active lifestyle. While estivating the frogs can withstand the loss of up to ~35% of their total body water. Estivation is considered a rather ‘light’ version of dormancy and hypometabolism since it involves rapidly reversible physiological changes. 

Characteristics of estivation include; conservation of fuel and water reserves to extend viability as long as possible, tolerance of the accumulation of waste products, and strong metabolic rate depression. Nitrogenous waste that is usually excreted into the water as ammonia is put to good use during estivation; the frogs convert ammonia to urea and accumulate high urea in their body fluids which provides osmotic resistance to water loss across their skin. Xenopus eggs have long been used a major laboratory model for studies of embryology and development and as a result, the Xenopus genome has been sequenced. In our lab, we are examining gene expression, miRNA regulation, and protein and enzyme responses to the stress of dehydration in this frog to understand the molecular underpinnings of estivation.