posted on 2007-03-01, 00:00authored byCarlos Davidson, Michael F. Benard, H. Bradley Shaffer, John M. Parker, Chadrick O'Leary, J. Michael Conlon, Louise A. Rollins-Smith
Environmental contaminants and disease may synergistically
contribute to amphibian population declines. Sub-lethal
levels of contaminants can suppress amphibian immune
defenses and, thereby, may facilitate disease outbreaks. We
conducted laboratory experiments on newly metamorphosed
foothill yellow-legged frogs (Rana boylii) to determine
whether sublethal exposure to the pesticide carbaryl would
increase susceptibility to the pathogenic chytrid fungus
Batrachochytrium dendrobatidis that is widely associated
with amphibian declines. We examined the effect of
carbaryl alone, chytrid alone, and interactions of the two
on individual survival, growth, and antimicrobial skin defenses.
We found no effect of chytrid, carbaryl, or their interaction
on survival. However, chytrid infection reduced growth
by approximately one-half. This is the first report of suppressed
growth in post-metamorphic amphibians due to infection
with chytrid. Rana boylii skin peptides strongly inhibited chytrid
growth in vitro, which may explain why chytrid exposure
did not result in significant mortality. Skin peptide defenses
were significantly reduced after exposure to carbaryl
suggesting that pesticides may inhibit this innate immune
defense and increase susceptibility to disease.