Emerging infectious diseases (EIDs) may reduce biodiversity and account for species extinctions. Therefore, it is urgent to understand the temporal and spatial dynamics of EIDs and to identify the factors associated with these dynamics. We studied seasonal and elevational patterns of prevalence and intensity of Batrachochytrium dendrobatidis (Bd), a chytrid fungus that causes chytridiomycosis, an EID associated with amphibian declines worldwide. We studied eight pond-breeding species that persisted after an epizootic at three low- and three mid-elevation ponds located in forests where population declines occurred in Central America. We visited each pond three times over the rainy season to sample for Bd and quantify frog density. We recorded air temperature and water temperature at each pond. We conducted repeated measure tests to assess prevalence and intensity variation over time and between elevations, and included frog density, air temperature, and water temperature as covariates. We expected infected frogs at all ponds. We predicted higher prevalence and intensity of the infection at mid-elevation and later in the season, since cooler conditions favor Bd growth. We predicted frog density to affect Bd prevalence since infection increased faster in riparian areas, where frogs congregate, than terrestrial areas during an epizootic in Panama.
Results/Conclusions
We analyzed 1288 samples and detected Bd in all six ponds and in six of the eight species. Prevalence and intensity showed similar patterns over the rainy season and between elevations. Elevation and time interacted to affect Bd prevalence (F2,8=4.12, p=0.05). Bd had higher prevalence at the beginning of the rainy season at mid-elevation ponds and dropped to almost 0% by the end of the season, while remaining below 10% in low-elevation ponds. Elevation and time interacted to affect Bd intensity (F2,8=9.09, p=0.008) and intensity of infection was low in all ponds. Frog density did not affect Bd prevalence (F1,7=4.75, p=0.06). Mean air and water temperature were within Bd optimal growth temperature but did not affect Bd prevalence or intensity. We conclude that season and elevation interact to affect Bd levels. Air temperature, water temperature, and frog density may not be the principal factors influencing Bd dynamics in Neotropical frogs after an epizootic. Six pond-breeding species are possible reservoirs of Bd infection and low Bd intensity may explain why these species do not go extinct during Bd epizootics. Variations in levels of Bd throughout time in species that persist after the epizootic have implications for local conservation and management programs.
