Print PageClimate is an important determinant of disease processes, especially for ectotherm hosts. Temperature and thermal acclimation have been shown to influence amphibian susceptibility to the pathogenic chytrid fungus Batrachocytrium dendrobatidis (Bd), which has been implicated in hundreds of declines and extinctions worldwide. Moisture might also be an important environmental driver of susceptibility to Bd for terrestrial amphibians, because Bd zoospores require an aquatic medium to spread across amphibian skin. Our recent work suggests that temperature influences Bd infections in wild populations of red-spotted newts (Notophthalmus viridescens). We therefore conducted a controlled-temperature experiment with juvenile newts to test for interactive effects of temperature (exposed at 15°C or 25°C), newt acclimation status (acclimated to 15°C or 25°C), and moisture (low, medium, or high soil moisture content) on susceptibility to Bd infection. We used 60 independently controlled incubators to manipulate temperature, providing true replication of the temperature, acclimation, and moisture treatments. Two newts were held within each incubator, in individual containers. Following a 4-week acclimation period, one newt per incubator was exposed to Bd. Bd loads were assessed using quantitative PCR of skin swabs at 2 and 4 weeks post-exposure, and survival was recorded for 6 weeks.
Results/Conclusions
Both moisture and temperature influenced newt susceptibility to Bd infection, with the highest Bd loads and Bd-induced mortality in the colder and wetter treatment combination. Furthermore, acclimation status significantly affected Bd loads on newts in the wet treatment, with unacclimated newts having higher Bd loads at both temperatures. These results are comparable to acclimation effects observed in our previous experiment, in which unacclimated Cuban treefrogs (Osteopilus septentrionalis) were more susceptible to Bd infection, though only at the warmer temperature. More work will be necessary to assess the generality of these findings to other amphibians and ectotherms. These results further indicate that temperature and acclimation effects on Bd infection are context-dependent, and might only be observed when additional factors, such as moisture, are conducive for infection to occur. Because climate factors like temperature and precipitation vary semi-independently in natural systems, this type of context-dependency should be considered when predicting effects of climate on Bd-induced amphibian extinctions.
