Biogeochemical and Ecological Impacts of Amphipod Circoviruses in Great Lakes and Southern California

**Project Completed**

Project PIs:
Ian Hewson (Department of Microbiology)
Lars Rudstam (Department of Natural Resources)

Several years of research into invertebrate-associated viruses have highlighted the occurrence of a class of small, circular, replication initiator protein-encoding single-stranded DNA (CRESS-DNA) viruses in marine and freshwater arthropods, including the water flea Daphnia spp. (Hewson et al., 2013), copepods Labidocera aestiva and Acartia tonsa (Dunlap et al., 2013) and amphipod Diporeia sp. (Hewson et al., 2013). The viruses are both active in replication, and present at high prevalence in natural populations. In Daphnia mendotae, prevalence was significantly correlated to mortality (r2 = 0.79) over seasonal cycles of abundance (Hewson et al., 2013). In cell cultures of experimentally infected Spodoptera frugifera (sf9) cells, circoviruses caused enhanced mortality and slower cell growth than in uninfected cells.

Despite our observations of circoviruses across a range of crustaceans, we know remarkably little about how they affect their hosts, and moreover how these effects may alter their host’s roles in biogeochemical cycles or food webs. In this project, our focus is on amphipods, targeting the freshwater taxon Diporeia sp in the laurentian Great Lakes, and the kelp amphipod Peramphithoe femorata. Both organisms are important to aquatic habitats for different reasons. Diporeia is a major consumer of settled spring bloom materials, and has experienced significant decline in geographic range in the last 20 years for reasons that are not totally clear. It is a major food source for larval fish. Peramphithoe on the other hand is a major consumer of detrital giant kelps on the US West Coast, which are threatened due to nutrient pollution and ocean-scale climatic phenomena, like el nino.

P1020091Peramphithoe femorata

This project was the first to gauge how viruses affect the ecological and biogeochemical roles that amphipods play in their respective habitats. We first examined the prevalence and viral load of both species amongst variable populations to understand their relationship to host food quality (C:N ratio, lipid content, etc). We then performed inoculation trials with their viruses in mesocosms to understand their impacts on key biogeochemical process, including NH4+ flux into overlying waters, decomposition of plant material, bacterial production, and inorganic nutrient transformation.

Work that has been performed so far on this project can be found via the links below:

Research Expedition: The BATS Validation Cruise BVAL-98, October 2014

Research Expedition: Santa Catalina Island, January 2015

Research Expedition: Great Lakes Environmental Monitoring Cruise, June – August 2014

Publications arising from this work are below:

Gezon N, Hawick D, Hewson I, Strychar K (in press) “Surveying circular rep encoding single stranded DNA viruses in quagga mussels (Dreissena rostriformis bugensis) and the central Lake Michigan benthos” Journal of Great Lakes Research

Hewson I (2019) “Technical pitfalls that bias comparative microbial community analyses of aquatic diseases” Diseases of Aquatic Organisms. 137: 109-124

Hewson I, Bistolas KSI, Button JB, Jackson EW (2018) “Occurrence and seasonal dynamics of RNA viral genotypes in three contrasting temperate lakes” PLoS One 13: e0194419

Bistolas, KSI, Besemer RM, Rudstam LG, Hewson I (2017) “Distribution and Inferred Evolutionary Characteristics of a Chimeric ssDNA Virus Associated with Intertidal Marine Isopods” Viruses 9: 361

Bistolas KSI., Rudstam L.G., Hewson I., (2017) “Gene expression of benthic amphipods (genus: Diporeia) in relation to a circular ssDNA virus across two Laurentian Great Lakes” PeerJ, 5:e3810

Bistolas KSI, Jackson EW, Watkins JM, Rudstam LG, Hewson I (2017) “Distribution of circular single stranded viruses associated with benthic amphipods of the genus Diporeia in the Laurentian Great Lakes”. Freshwater Biology. 62:1220-1237

Bistolas KSI, Button JB, Jackson EWJ, Hewson I (2016) “Circoviruses of Crustaceans” pp. 419-421 in Kibenge SB and Godoy M “Aquaculture Virology” Elsevier, New York, 549pp.

Jackson EW, Bistolas KSI, Button JBB, Hewson I (2016) “Novel circular single-stranded DNA viruses among an asteroid, echinoid and holothurian (Phylum: Echinodermata)”. PLoS One. DOI:10.1371/journal.pone.0166093

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