Temperature-mediated pathology: Differential effects of climate change on the pathogenic trematode, R. ondatrae, and its intermediate host, H. trivolvis

Background/Question/Methods Growing concern focuses on how forecasted changes in climate are likely to affect host-parasite interactions and emerging infectious diseases. Because parasites and their host species may respond differently to climate change (e.g., due to differential Q₁₀ rates), shifts in temperature will likely alter the resultant patterns of abundance and pathology. We studied the influence of temperature on the growth and reproductive rates of the trematode parasite, Ribeiroia ondatrae, its snail host Planorbella trivolvis, and their interactions. We exposed 450 laboratory-reared snails to either fecal material containing embryonated R. ondatrae eggs, or to uninfected fecal material, prior to splitting them into three temperature treatments (13, 21, and 26 ºC). 

Results/Conclusions

While both host and parasite exhibited strong responses to temperature, these patterns differed between the organisms. At 13ºC, R. ondatrae was unable to complete development within the snail, whereas snail hosts continued to actively produce eggs. Furthermore, the temperature-mediated change in infected snail growth rates (Q₁₀) was twice as high as for uninfected snails. This indicates that temperature may have a disproportionate effect on the growth rate of the parasite relative to its host. In the event of continued climatic warming, this could lead to earlier seasonal reproduction and greater increases in abundance of R. ondatrae relative to H. trivolvis. Moreover, parasite-induced pathology in snails was amplified at higher temperatures, such that overall egg production in infected snails was reduced by 65% at 26ºC compared to a 42% and a 33% reduction at the 21 and 13ºC treatments respectively. Taken together, these results indicate that temperature may be an important determinant of the abundance of parasites relative to their hosts as well as to host pathology.