Infected frogs vulnerable to water loss during sloughing

Abstract

A plague is sweeping across the planet and amphibians are its victims. Michel Ohmer from the University of Pittsburgh, USA, explains that the disease, chytridiomycosis, is caused by a fungus, Batrachochytrium dendrobatidis, which infects the skin; sufferers go off their food, become dehydrated and lethargic, and eventually die of heart failure. In addition, the frogs moult more often in a bid to rid themselves of the infection. Ohmer, Catherine Russo, Rebecca Cramp and Craig Franklin from the University of Queensland, Australia, wondered whether sloughing the skin more often might contribute to the dehydration that the frogs experience and whether smaller frogs were more vulnerable to this water loss than larger animals.While the team focused on green tree frogs (Litoria caerulea), they also investigated the effects of the fungus on striped marsh frogs (Limnodynastes peronii), Fletcher's frog (Lechriodus fletcheri), the spotted marsh frog (Limnodynastes tasmaniensis) and the ornate burrowing frog (Platyplectrum ornatum). After checking how often the uninfected animals shed their skin, the team gently blew air over the frogs while measuring their weight as they lost water. The team then infected some of the frogs with the fungus and waited for the infection to take hold before measuring their water loss rates again before, after and while shedding their skins.Comparing the infected and uninfected frogs, the team noticed that the average length of time between the frogs shedding their skin dropped from ∼3 days to a little over 2 (57 h) when the frogs were infected. And when the team monitored the effects of the infection on the animals, they were pleased to see that the spotted marsh frogs were relatively resilient, showing no signs of the infection. Although it was clear that the water loss rates of the infected frogs rocketed by over 230% when they were active, the inactive animals were less vulnerable to dehydration. In addition, the smaller frogs shed their skins more frequently than the larger animals and dehydrated more rapidly. ‘This may in part explain the higher mortality rates typical for small and juvenile frogs infected with Batrachochytrium dendrobatidis’, says Russo, and the team is keen to learn more about the effect that the fungus has on amphibian skin to better understand which species are vulnerable and which could outfox the deadly infection.