Water mould exposure induces enzymatic antioxidant defences in embryos of Elachistocleis bicolor (Anura: Microhylidae)

Abstract

Water moulds are pathogens of amphibian eggs and embryos. However, little is known about oxidant or antioxidant status of amphibians in response to stress caused by water moulds. We exposed embryo stages of Two-colored Oval Frogs (Elachistocleis bicolor (Guérin-Méneville, 1838)) to a Saprolegnia-like species of water mould to explore homeostatic adjustments by the shifting of oxidative stress markers. We also tested whether water mould infection affected survivorship, hatching time, and morphology of hatching embryos. We found that the Saprolegnia-like species is a genuine stressor and substantially altered the physiological state of E. bicolor embryos. Among antioxidant defences, superoxide dismutase (SOD) and glutathione S-transferase (GST) activities increased in embryos exposed to the Saprolegnia-like species. However, no difference in lipid peroxidation levels was found between treatments, which might indicate that SOD and GST activations could be enough to prevent oxidative damage. Finally, we found higher mortality and number of malformations in the water mould treatment. We showed the stressful effect of water moulds on amphibian embryos, evidenced by the activation of their antioxidant system, and reveal the importance of considering physiological stress markers as key information when studying the potential consequences of disease outbreaks in the ecology and conservation of amphibians.