How Temperature, Pond-Drying, and Nutrients Influence Parasite Infection and Pathology

The rapid pace of environmental change is driving multi-faceted shifts in abiotic factors that influence parasite transmission. However, cumulative effects of these factors on wildlife diseases remain poorly understood. Here we used an information-theoretic approach to compare the relative influence of abiotic factors (temperature, diurnal temperature range, nutrients and pond-drying), on infection of snail and amphibian hosts by two trematode parasites (Ribeiroia ondatrae and Echinostoma spp.). A temperature shift from 20 to 25 °C was associated with an increase in infected snail prevalence of 10-20%, while overall snail densities declined by a factor of 6. Trematode infection abundance in frogs was best predicted by infected snail density, while Ribeiroia infection specifically also declined by half for each 10% reduction in pond perimeter, despite no effect of perimeter on the per snail release rate of cercariae. Both nutrient concentrations and Ribeiroia infection positively predicted amphibian deformities, potentially owing to reduced host tolerance or increased parasite virulence in more productive environments. For both parasites, temperature, pond-drying, and nutrients were influential at different points in the transmission cycle, highlighting the importance of detailed seasonal field studies that capture the importance of multiple drivers of infection dynamics and the mechanisms through which they operate.