The role of viruses in biological invasions: friend or foe?

Biological invasions occur when plants, animals, or microbes are introduced to a new geographic region, then spread and have negative consequences for the local ecosystem. Across both plant and animal hosts, viruses can play diverse roles in biological invasions. First, viruses can either decrease or increase the impacts of biological invasions by their hosts. Introduced hosts commonly leave behind many viruses from their native ranges, which may allow the hosts to achieve greater fitness and thus dominate in their introduced ranges. Viruses that do infect introduced hosts may reduce invasive host fitness and impacts. However, many viruses that infect introduced hosts also infect native hosts and may have more severe impacts on the native hosts. Second, viruses can also be invasive species themselves. While many viruses are believed to be introduced, it is challenging to differentiate between those that are native and those that are not. Third, many viruses are transmitted by vectors, which can also be introduced to new regions. Introduced vectors can increase virus transmission rates, altering host communities and ecosystems. Further advancing our understanding of the role of viruses in biological invasions will require research that integrates the systematics, biogeography and ecological history of hosts, vectors, and viruses.