COS 232-4 - Temperature variability and salt pollution interact to alter parasite susceptibility in larval amphibians

Background/Question/Methods

Wild populations face unprecedented pressure from an assortment of anthropogenic environmental changes and parasites. We sought to understand how host-parasite interactions are affected by the interactive effects of multiple environmental stressors. We focused on American bullfrog tadpoles (Lithobates catesbeianus) that can become infected by several parasite species (e.g., Echinostoma paryphium parasites and Batrachochytrium dendrobatidis; “Bd”) and are affected by abiotic stressors including road salt and variable temperatures attributed to climate change. In a multi-phase laboratory experiment, we exposed tadpoles to 2 salt treatments (0 and 1.5g/L added NaCl; a sublethal concentration) and 2 temperature treatments (constant 23°C and fluctuating between 20°C and 25°C) for 14 days. We then exposed these tadpoles to one of three parasite treatments (none, Echinostoma only, and Bd & Echinostoma together). We recorded morphological measurements (length, mass, stage) and quantified infection prevalence and intensity.

Results/Conclusions

We found that elevated salinity interacted with our temperature and parasite treatments to alter Echinostoma infection. Specifically, we found an interaction between salinity and temperature treatments where tadpoles in fluctuating temperatures with Bd and Echinostoma together were infected with more parasites when exposed to elevated salinity compared to our control (no NaCl added) salinity treatments. We also found an interaction of the parasite and salt treatments, where Bd and Echinostoma together with elevated salinity treatments had higher infection loads than Echinstoma only and baseline salinity. We did not detect any effect of our treatments on mass, length, or developmental stage. Together, these results indicate that road salt runoff will alter parasite infection in larval amphibians, but the effects of salinity can vary with other abiotic and biotic conditions. More broadly, our results suggest that salt pollution in freshwater systems and fluctuating temperatures associated with climate change can influence parasite infection in tadpoles.