Abstract
Amphibian populations worldwide are currently experiencing unprecedented declines due to the combined effects of emerging infectious disease and climate change. The skin is the first line of defence in preventing establishment of pathogens and associated infections. Although amphibians undergo regular sloughing of the outer layer of the skin, the potential for regular sloughing to play a role in influencing cutaneous microbial populations and pathogens has been largely overlooked. In the present study, we assessed the effect of skin sloughing on cultivable cutaneous bacterial abundance in the green tree frog (Litoria caerulea). We also examined the effects of temperature and hydric environment on sloughing frequency and microbial re-establishment rates. Our data showed that cultivable cutaneous bacterial abundance was significantly reduced by sloughing events, and frogs kept at 'summer' temperatures (23-33°C) sloughed almost twice as frequently as those maintained at 'winter' temperatures (13-23°C). No effect of hydric environment on sloughing frequency was observed, but we did find that sloughing in L. caerulea appeared to be linked to ambient light cycles. Examination of the effect of sloughing on microbial recolonization indicated that at cool temperatures, an extended intermoult interval allowed microbial abundance to reach higher levels than at warmer 'summer' temperatures (when the intermoult interval was significantly reduced). Our data suggest that sloughing may significantly influence the establishment and/or maintenance of cutaneous bacterial populations (pathogenic, mutualistic and/or commensal) and this, in turn, may be affected by environmental factors, such as ambient light and temperature. These findings are likely to be important for our understanding of the ecology of skin-based pathogens, such as the amphibian chytrid fungus, Batrachochytrium dendrobatidis.
Highlights
The skin is considered to be a vital component of the immune system because it presents an initial barrier to the establishment of pathogens and associated infections in the body (Proksch et al, 2008; Bos and Luiten, 2009)
Understanding the protective capacity and physiological processes of the skin in relation to varying environmental factors is of interest to current research regarding global environmental change and the emergence of infectious diseases (Harvell et al, 2002; Belden and Harris, 2007; Feder, 2010), because these changes may play a part in the decline of species susceptible to skin-based diseases (Daszak et al, 1999, 2003; Lips et al, 2008; Anchukaitis and Evans, 2010)
To ensure the continued integrity of the skin surface, vertebrates undergo a skin-renewal process called moulting, or desquamation, whereby the outer stratum of the skin separates from the underlying skin layers and is lost to the environment
Summary
The skin is considered to be a vital component of the immune system because it presents an initial barrier to the establishment of pathogens and associated infections in the body (Proksch et al, 2008; Bos and Luiten, 2009). Understanding the protective capacity and physiological processes of the skin in relation to varying environmental factors is of interest to current research regarding global environmental change and the emergence of infectious diseases (Harvell et al, 2002; Belden and Harris, 2007; Feder, 2010), because these changes may play a part in the decline of species susceptible to skin-based diseases (Daszak et al, 1999, 2003; Lips et al, 2008; Anchukaitis and Evans, 2010). The sloughing process is regulated hormonally via the thyroid, adrenal and pituitary glands (Taylor and Ewer, 1956; Jorgensen and Larsen, 1960, 1961, 1964; Jorgensen, et al, 1965; Budtz, 1979; Jørgensen, 1988); sloughing frequency and the associated length of the intermoult interval can be influenced by environmental conditions, including temperature, light and food availability (Bendsen, 1956; Taylor and Ewer, 1956; Stefano and Donoso, 1964; Larsen, 1976; Herman, 1992)
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