As an aquatic, generalist pathogen, ranaviruses infect more than 70 amphibian species and may play an important role in worldwide amphibian population declines. The role of ranaviruses in aquatic communities is complicated by the number of competent host species present. To examine the dynamics of ranaviruses in a multi-host assemblage, we conducted an outdoor mesocosm experiment manipulating amphibian species composition (1 vs. 3 species) and ranavirus exposure (exposed vs. not).
Our 60 day experiment was conducted in 120 L mesocosms filled with water, seeded with sterile leaf litter, covered mesh, and allowed three weeks for algal growth to simulate a natural pond environment. The experiment was divided into 1-host and 3-host treatments and then divided again into Ranavirus and Control treatments (n=6 replicates for each treatment). The 1-host treatments consisted of 33 naïve western toad larvae (Anaxyrus boreas), exposed to either 3 ranavirus infected conspecifics, or three conspecifics exposed to a sham inoculation. The 3-host species treatments consisted of 33 naïve larvae (11 Anaxyrus boreas, 11 Pseudacris regilla, 11 Rana cascadae) exposed to either 3 ranavirus infected conspecifics (one of each host species), or three conspecifics exposed to a sham inoculation.
Results/Conclusions
We found differences between the 1 and 3 host Ranavirus treatments. By day 60, in 1-host treatments, A. boreas experienced 35% mortality while A. boreas in the 3-host treatments experienced 100% mortality. In the control regimes, A. boreasmortality after 60 days was 22% in both treatments. These results appear consistent with amplification-- an increase in biodiversity amplifies the disease risk for a community.
There are a number of potential explanations for these results. It’s possible that one host species may tolerate infection longer, providing the virus with more transmission time to infect other hosts. It’s also possible that viral loads may vary greatly between species, altering local infection risks. To understand the role ranavirus plays in amphibian population declines, it will be important to consider the pathogen’s interactions with each potential host within an assemblage.