Persistence, Prevalence, and Load of Circoviruses in Marine and Lacustrine Amphipods

Benthic amphipods serve as keystone species in the Laurentian Great Lakes, mediating functional and structural diversity in profundal communities by contributing to net detritivory, herbivory, and sediment bioturbation. Long-term, lake wide annual monitoring programs depict progressive and severe (up to 90%) declines in populations of the dominant amphipod, Diporeia spp. between 1997-2015. The causative factors implicated in Diporeia decline remain unknown. However, previous metaviromic studies identified a well-represented CRESS-DNA virus associated with Diporeia from four of the five Great Lakes, excluding Lake Superior. Prevalence, load, and persistence of this single putative circovirus (LM29173) largely coincide with the severity of Diporeia decline in independent populations. This study builds upon assessments of circoviral prevalence and load from 2013, and identifies LM29173 as a persistent constituent of the Diporeia nanobiome over a multi-year sampling period. Furthermore, comparative analysis of Diporeia metaviromes from independent sampling sites in lakes with varying benthic profiles reveal several distinct patterns of viral consortia. Phylogenetic comparison of conserved replication initiator protein-like sequence elements places LM29173 in the context of circoviruses from similar lacustrine and marine microcrustacean hosts. While it is unclear if circoviruses are directly deleterious to amphipod hosts, it is apparent that CRESS-DNA sequence elements sharing similar features to LM29173 are ubiquitous in amphipod-associated metaviromes.