The ecology and evolution of multihost pathogens (e.g. hantavirus, avian influenza, chytrid fungus) can have dire consequences for human health, food security, and wildlife conservation. However, the ecological and evolutionary consequences of pathogen transmission among diverse hosts have been difficult to study since pathogen host ranges are often incompletely characterized and host distributions are often difficult to manipulate. We are developing an experimentally tractable animal model, hosts belonging to the Caenorhabditis genus and one of their natural pathogens, Orsay virus, to study the ecology and evolution of multihost pathogen interactions. Previous literature has reported that Orsay virus is a species-specific virus of C. elegans. However, this specificity was assessed using very few host species. Here, we conduct an exhaustive screen of Caenorhabditis species for which at least one wild isolate is available at the Caenorhabditis Genomics Center (CGC). We expose potential hosts to virus through the natural route of infection (in their food) and detect virus replication (using quantitative PCR to assess changes in virus-genome copies). We also transfer a subset of exposed hosts to virus-free environments for three passage cycles to see whether infection can be maintained in host populations without artificially adding virus.
Results/Conclusions
We currently have preliminary susceptibility data from 10 of 40 Caenorhabditis species, with more data expected soon. These preliminary data show that at least three species (C. elegans, C. tropicalis, and C. wallacei) are susceptible to Orsay virus infection. The preliminary data also show that at least 7 other species are not susceptible to infection. The patterns of host susceptibility are striking as C. tropicalis and C. wallacei are sister species and likely share traits that make them susceptible to virus infection. C. elegans, however, diverged from a common ancestor with them at least 30 million years ago, and our preliminary data show that C. inopinata, the sister species to C. elegans, and several species in the clade with C. tropicalis and C. wallacei, are not susceptible to infection. These data therefore suggest that virus susceptibility, whether due to host or pathogen evolution, has been gained or lost at least twice over the subset of species that have so far been tested. Future experiments involve quantifying the ecological dynamics of pathogen transmission within single and mixed host populations and exploring the evolutionary consequences of these conditions on Orsay virus evolution.