One downstream effect of biodiversity loss is the impact of host diversity on the reduction or amplification of disease risk in host populations. As part of a worldwide “Biodiversity Crisis”, amphibian populations have experienced declines and extinctions due to a variety of factors including the spread of generalist pathogens. The global decline of amphibian populations provides an opportunity to examine the relationship between disease and biodiversity.
To investigate the interrelationships among biodiversity and disease, we conducted laboratory experiments to examine host susceptibility and mesocosm experiments to examine community scale disease dynamics of the emerging pathogen, ranavirus, in three amphibian host species (Anaxyrus boreas, Pseudacris regilla, and Rana aurora). In laboratory experiments we exposed animals (n=28 per treatment) to ranavirus or a sham (control) and raised them through metamorphosis to quantify survival. We conducted outdoor experiments in mesocosms (n=6 per treatment) housing 33 naïve animals, of either 1 (A. boreas) or 3 (A. boreas, P. regilla, R. aurora) host species. To each mesocosm we added an additional three animals by treatment, either exposed to ranavirus or a sham (control). We quantified the survival of each species on day 30 and 60.
Results/Conclusions
In the mesocosm experiment, both 1 host and 3 host ranavirus treatments had reduced survival compared to controls which experienced an average of 23% mortality. Ranavirus treatments were significantly different with three host ranavirus treatments experiencing 100% mortality compared to 37% mortality in 1 host ranavirus treatments.
In mesocosm experiments, we found that ranavirus mortality increased with species diversity, evidence of an amplification effect. Based on the susceptibility of P. regilla to ranavirus, it is likely that the presence of this species in the 3 host mesocosm treatments caused the observed amplification. This suggests a specific host-pathogen relationship can drive disease dynamics among multiple species within an assemblage. Here we tested two potential assemblages, whether changes in diversity will cause amplification in natural systems is likely to depend on how communities assemble; if highly susceptible species, such as P. regilla, occur in both low- and high-diversity systems, increased diversity could alternatively have no effect or even dilute transmission.