Oral Presentation 64th International Conference of the Wildlife Disease Association 2015

Skin sloughing and susceptibility: the role of skin processes in the susceptibility of amphibians to chytridiomycosis (#26)

Michel E B Ohmer 1 , Rebecca L Cramp 1 , Craig R White 1 , Craig E Franklin 1
  1. The University of Queensland, St. Lucia, QLD, Australia

The zoosporic fungus Batrachochytrium dendrobatidis (Bd), which is the causative agent of the amphibian disease chytridiomycosis, has resulted in the declines and extinctions of amphibians worldwide. This generalist pathogen infects a wide range of amphibian hosts, and a combination of ecological, physiological and environmental variables likely influence differences in susceptibility within and between species. Given Bd infects the keratinised skin of amphibians, variation in susceptibility to Bd may also be influenced by aspects of skin functioning, such as the rate of routine skin sloughing or shedding. Previous work has demonstrated that sloughing may be involved in immune defence by regulating the growth of skin-associated microbes, and thus could play an important role in the pathogenesis of chytridiomycosis. To examine the relationship between skin sloughing and disease progression, we exposed adult Australian green tree frogs (Litoria caerulea) to Bd, and monitored the change in sloughing rate and infection load over time using infrared cameras and quantitative PCR. Sloughing rate increased with Bd infection load in infected frogs, however the act of sloughing did not reduce Bd load on the ventral skin surface.  In L. caerulea, a susceptible species, sloughing does not appear to limit the progression of disease. Rather, increased sloughing may actually exacerbate the loss of physiological homeostasis seen in terminally ill frogs by further inhibiting water and electrolyte transport across the skin. By measuring sloughing rates directly for the first time, our results provide insight into how variation in sloughing may influence susceptibility to chytridiomycosis. We are currently examining the efficacy of skin sloughing in reducing Bd loads on the skin of amphibians with low susceptibility to chytridiomycosis. Understanding the factors driving variation in susceptibility can improve our predictions of amphibian responses to Bd in wild populations, allowing for better species conservation planning.