Award: OCE-1356964

Viruses play enormously important roles in aquatic ecosystems. They can cause significant mortality of aquatic animals, which in turn impacts food webs and enhances biodiversity. Yet, we know little about the magnitude of these impacts in non-aquacultured marine invertebrates. In this project, we examined the impacts of a newly-discovered group of viruses, the circular rep-encoding single stranded DNA (CRESS-DNA) viruses, on an ecologically important microscopic crustacean (Amphipods) in the Great Lakes and coastal Pacific Ocean. A critical first step in understanding these impacts was to determine their diversity, geographic and temporal distribution, and to examine how these viruses influence their hosts. We found that CRESS-DNA viruses are enormously diverse in amphipod tissues and were present in almost every sample we tested. While they did not cause mortality of their hosts when uninfected amphipods were infected, they expressed genes that indicated the virus re-arranged the ways they made new cells and metabolized. We also found that the number of CRESS-DNA viral particles per individual (i.e. viral load) correlated best with the sub-species of amphipod, and that there was no relationship between viral load and the nutritional quality (measured by lipid content and ratio of carbon to nitrogen) of their host. Furthermore, the degree of amphipod infection did not relate to their impacts on microbial activities in surrounding waters. These investigations conclude that while CRESS-DNA viruses infect many amphipods, they do not significantly impact their host ecology, and therefore have no discernible impacts on their roles in ecosystems. Our results are significant because it was previously assumed that viruses always imparted negative impacts on their hosts, and many studies ingenerate mortality from the presence of specific viral type. CRESS-DNA viruses are widely seen in surveys of viruses free in the environment. However, our work demonstrates that making this assumption is not necessarily valid. This project has generated considerable and transformative knowledge about the diversity of viruses infecting aquatic invertebrates, and provides context for ecological interpretation of animal viruses discovered in wider microbial surveys. This project trained 3 graduate students, 2 undergraduates in techniques of metagenomics and invertebrate virology. The project led to the scientific publication of 5 peer-reviewed scientific papers, 1 book chapter, and was disseminated at 3 scientific conferences and 2 invited seminars at other institutions. The project also trained an alternate-track high school student from Lansing High School in invertebrate virology. Last Modified: 06/10/2019 Submitted by: Ian Hewson