WOODHAMS, Douglas/C; ALFORD, Ross/A; BRIGGS, Cheryl/J; ROLLINS-SMITH, Louise/A; Vanderbilt University; James Cook University; Univ. of California, Berkeley; Vanderbilt University: Disease-Associated Amphibian Population Declines Fit Model of Pathogen Growth and Host Innate Immunity

The chytrid fungus, Batrachochytrium dendrobatidis (Bd), is the agent of chytridiomycosis, a globally emerging infectious disease of amphibians. Bd develops through multiple stages in a single host including a mobile infectious zoospore stage, a sessile developing sporangium, and a zoospore-releasing zoosporangium. As in other organisms with complex life-histories, temperature-regulated trade-offs may exist between growth rate and development rate. Specifically, at 8&deg C larger numbers of more active zoospores are produced and remain infectious for a longer period of time than at 23&deg C. However, growth rate is significantly greater at the higher temperature. When these in vitro data are applied to a delayed-differential model of population growth, the outcome fits the observed pattern of chytridiomycosis outbreaks occurring at high elevations or during the cold season where some amphibian populations have declined in Australia, North and Central America, and Spain. In addition to temperature and biogeography, disease may be regulated by host ecology, behavior, life-history, or immune function. The immunological resistance to infection has not been well characterized; however, temperature may also influence the innate antimicrobial defenses of amphibian skin peptides.