Files
Abstract
Chytridiomycosis is an emerging infectious disease of amphibians that has causedpopulation declines in North and Central America and Australia. The disease is caused bythe fungus Batrachochytrium dendrobatidis. Factors contributing to susceptibility ofamphibians to this disease are not well known. Temperature has been suggested as a key factor since chytridiomycosis is thought to occur more frequently at cool high-elevation sites where enigmatic amphibian declines have been observed. To study the effects of temperature on susceptibility to chytridiomycosis, we experimentally exposedGastrotheca peruana at 18 and 23C and Plethodon metcalfi and Desmognathusmonticola at 8 and 16C to B. dendrobatidis. Mortality of infected G. peruana was higherat 18C than at 23C. Mortality of P. metcalfi due to B. dendrobatidis was higher at 8Cthan at 16C. Therefore, temperatures at the low end of the range suitable to maintain the health of amphibians appear to increase susceptibility to the pathogen.Phylogeny is also a possible factor in susceptibility, since a few studies indicatesalamanders may respond differently to infection with Batrachochytrium dendrobatidis.We compared infection of Plethodon metcalfi and Desmognathus monticola to that ofanuran species. Infected salamanders exhibited few of the clinical signs associated withB. dendrobatidis infection; however, they exhibited histological signs of disease similarto those previously observed in other salamanders. Some salamanders may have cleared infection. The amphibian immune system likely plays a role in susceptibility tochytridiomycosis.Cutaneous peptides secreted from amphibian skin are effective at inhibitinggrowth of Batrachochytrium dendrobatidis in vitro. To examine the role of cutaneouspeptides in vivo we depleted Rana catesbeiana of peptides and then exposed them toabout 10 million B. dendrobatidis zoospores. All frogs became infected with B.dendrobatidis, as determined by PCR; however no clinical or histological signs of diseasewere observed. The natural mixtures of peptides of R. catesbeiana had low effectivenessagainst B. dendrobatidis in vitro. Therefore antimicrobial peptides are not the sole sourceof resistance to chytridiomycosis in R. catesbeiana. Further research is required on thefactors discussed here and the many others likely involved in susceptibility tochytridiomycosis.