The availability of freshwater for humans and other organisms is rapidly changing, and urbanization, agriculture, and an increasing human population are driving causes. Changes to the duration and amount of surface freshwater might have profound consequences for wildlife that require water to complete their life cycle. Many amphibian species need freshwater for larval development, and pond drying might not only reduce their survival to and after metamorphosis, but also impact their long-term ability to fight off diseases.
We explored the effects of pond drying on the development, growth, survival and immune function of tadpoles and post-metamorphic frogs. We found that when frogs developed as tadpoles in drying ponds, they had lower survival, were smaller at metamorphosis, and had reduced or altered immune function. Small frogs that metamorphosed early, regardless of drying treatment, were also found to have reduced immune function, demonstrating potentially long-term consequences of early developmental stress. Interestingly, we found that under drying conditions, males were able to metamorphose more quickly than females, indicating that more males than females could successfully escape a drying pond.
Water availability is essential for amphibians that breed in ponds and streams. Human induced environmental change is decreasing the availability of water and increasing the threat that environmental stressors pose for wildlife. Our research demonstrates that increased pond drying rates might decrease frog survival, influence females more than males, and negatively impact immune function. Reduced immune function might make amphibians more susceptible to pathogens and parasites common in their environments and contribute to ongoing global population declines. Overall, we demonstrate the importance of changes in the larval environment for amphibian health and discuss how these changes might impact amphibian populations into the future.