Invasive species are one of the leading threats to biodiversity. Infectious disease can enter the mix in several ways. Invasive species, on average, leave behind the majority of their parasites when they become established in new regions and are slow to acquire new parasites in the invaded regions. This pattern has broad implications for the concept of enemy release. I am interested in examining which types of parasites have the highest potential to confer enemy release advantages to invasive species. In Colorado, we completed a study on invasive New Zealand mudsnails (Potamopyrgus antipodarum), which are spreading throughout North America and have become established in Boulder Creek. We found snails to be unparasitized and that stream temperature, nutrients, and hardness are all significant predictors of fecundity in these tiny parthenogenic invaders. These novel findings will help inform ecological niche modeling efforts that predict the spatial extent of habitats that are prone to invasion by New Zealand mudsnails.
The flip-side to invasive species and enemy release is pathogen pollution. In many cases, invasive species leave their parasites behind, but a few of the parasites and pathogens that make the journey with their intrepid hosts can wreak havoc in the new environments. Examples of this phenomenon include whirling disease in North American salmonid fishes, canine distemper in African carnivores, avian malaria in Hawaiian birds, and chytridiomycosis (caused by Bd) in amphibians. In my Conservation Medicine course, I involved the students in beginning a large meta-analysis to examine the trends of emerging infectious diseases in wildlife at the global scale. We are in the process of analyzing data from this study and have amassed over 600 cases of emerging infectious disease events globally across vertebrate animals. We look forward to sharing these results with a wide audience.