Louise A. Rollins-Smith Vanderbilt University Medical Center
Many species of amphibians (frogs, toads, and salamanders) are currently in decline, and the rate of extinctions is more rapid than for birds or mammals. There are many possible causes including loss of habitat, pollution, and disease. Recent declines are linked to a lethal skin disease that is caused by a chytrid fungus. Disease outbreaks continue to occur in a pattern consistent with the spread of a new pathogen into susceptible populations. This global ecological crisis provides a unique opportunity to study immune mechanisms of disease resistance in a wildlife species. Current studies suggest that some species are less susceptible to this disease than others, and these differences in susceptibility are correlated with differences in skin defenses. This project will examine the question of whether antimicrobial peptides in the skin secretions of amphibians are a major immune defense mechanism against the chytrid fungus and whether species that are more resistant will have more effective antimicrobial peptide defenses. This will be tested by characterizing the antimicrobial peptides from selected species in Panama and the U.S. that are known to be susceptible or resistant to disease and determining their anti-chytrid potency. Another question that will be addressed is whether the strong selection pressure of a chytrid infection may select for individuals that, due to genetic variation, can express rare beneficial antimicrobial peptides. If so, beneficial peptides may be detectable in survivor populations in comparison with naive susceptible populations. This will be tested where amphibian populations exist in a chytrid-free zone as well as being present in areas where a wave of disease and population losses has occurred, yet some survivors exist. This four-year project has great potential for training students (including under-represented minorities) at the postdoctoral, graduate, and undergraduate levels. It will enhance ongoing partnerships with an international group of ecologists, physiologists, biochemists, and amphibian disease specialists addressing the problem of global amphibian declines. A greater understanding of the dynamics of antimicrobial peptide defenses and pathogen interactions may provide insights into mechanisms by which amphibians evolve resistance to skin pathogens. Results may suggest species that are especially vulnerable to chytrid fungal disease and should be the focus of greater conservation efforts.
