Climate change and amphibian disease: combined influences of hydroperiod and parasitism on larval development

Background/Question/Methods

Climate change has been shown or hypothesized to affect disease through various means. The effects of temperature have largely been the focus to date; however, hydroperiod may also be an important consideration for certain hosts and pathogens. Both precipitation and warmer temperatures (resulting in increased evaporation) are expected to impact hydrological regimes. Hydroperiod is crucial for amphibian breeding and larval development, particularly for species using temporary aquatic habitats.   Many larval amphibian species exhibit phenotypic plasticity in terms of developmental rate in response to habitat drying but this could be affected by infection with the trematode Ribeiroia ondatrae, a pathogenic macroparasite associated with larval mortality, delayed development, and various malformations.  We examined the combined effects of R. ondatrae and hydroperiod on the developmental plasticity of larval Pacific chorus frogs (Pseudacris regilla) using experimental mesocosms. We employed a factorial design that included a shortened hydroperiod and exposure to R. ondatrae for half of the tadpoles in each tank, recording developmental stage and mass at the end of the experiment, as well as those who metamorphosed early. 

Results/Conclusions

Shortened hydroperiod and R. ondatrae infection had additive effects on tadpole developmental stage since uninfected individuals experiencing rapid water draw-down were the most developed.  A similar additive effect was observed for the number of individuals who emerged early (before experiment end).  In contrast, an interactive effect of parasitism treatment and short hydroperiod was seen for early emergence since those in the parasitism treatment fared better under normal evaporative conditions but were worse off than the no parasite treatment in the dry-down condition.  Given that uninfected individuals tended to fare better in general but those in the parasitism treatment performed best of all in certain cases, infected tadpoles may be inferior competitors.  Our results suggest that a shorted hydroperiod in combination with parasite infection could have implications for larval amphibian ability to complete development or escape poor conditions, indicating that the effects of climate change on this host-parasite system will be difficult to predict without considering multiple factors.