Distribution of circular single-stranded DNA viruses associated with benthic amphipods of genus Diporeia in the Laurentian Great Lakes

Benthic amphipods of genus Diporeia are key indicators of ecosystem health and were the most abundant invertebrate in the four deep Laurentian Great Lakes until the mid-1990s. The mechanism(s) responsible for declines in Diporeia abundance in Lakes Huron, Michigan and Ontario remain contentious. A previous study identified a circular replication initiator protein-encoding single-stranded (CRESS) DNA virus, LM29173, associated with Diporeia populations. This study surveys the distribution of CRESS-DNA viral genotypes in amphipods from several populations and investigates the relationship between viral presence and nutritional quality of the amphipod. We show that CRESS-DNA virus-like sequences are common in Diporeia nanobiomes, and are detectable as free particles in virioplankton. Among three identified CRESS-DNA viral genotypes (LM29173, LM122 and LH481), LM29173 is a recurrent and prevalent constituent of Lake Michigan and Lake Huron Diporeia-associated viral consortia, with genotype load averaging 726-3,643 copies mg(-1) of tissue. LM29173 abundance coincides with amphipod haplotype demographics, and was more prevalent among Diporeia from the southern clade (Lakes Michigan, Huron, New York Finger Lakes) than northern clade (Lake Superior), irrespective of the state of population decline. We expected that the association of CRESS-DNA viruses would impart costs to amphipod physiology. However, viral load of LM29173 did not correlate with amphipod nutritional quality (lipid content, C:N stoichiometry).