Date Approved

12-2017

Graduate Degree Type

Thesis

Degree Name

Biology (M.S.)

Degree Program

Biology

First Advisor

Kevin Strychar

Second Advisor

Charlyn Patridge

Third Advisor

James McNair

Fourth Advisor

Ian Hewson

Fifth Advisor

Doug Haywick

Academic Year

2017/2018

Abstract

Globalization and resulting increases in international trade has allowed for the movement of species between almost all ecosystems on Earth. The Great Lakes in particular has seen a number of high impact invasive species that have moved in following the opening of the lakes to intercontinental shipping trade. This research specifically focuses on the benthic community of Lake Michigan which has seen significant community shifts including declines of the amphipods Diporeia spp. and the expansion of invasive quagga mussels (Dreissena rostriformis bugensis). Little is known about the viral community in the benthos of Lake Michigan and how it may have changed with the establishment of invasive species. I am interested specifically in a group of important, potentially pathogenic viruses, known as Circular Rep Encoding Single Stranded DNA viruses or CRESS-DNA viruses. Here I examined samples from the central Lake Michigan benthos including quagga mussels and sediment cores using metaviromics and qPCR to examine a specific CRESS-DNA virus-like sequence. A specific Diporeia spp. associated CRESS-DNA virus (circovirus) known as LM29713 (identified in Hewson et al., 2013) was investigated using qPCR where it was found to be present throughout nearshore and offshore sediment cores. My results suggest that the virus is endemic and has been present in Lake Michigan as long as its host Diporeia spp. have been present. I also completed a metavirome analysis of all the CRESS-DNA virus-like sequences found in an offshore sediment core and quagga mussels samples. A comparison of all the different CRESSDNA virus-like sequences found in the samples using a heat map shows a greater overlap in the viruses found in the quagga mussels of different size and ages and a larger difference between the viruses found in the sediment core layers. Overall the CRESS-DNA virus-like sequences reads found in each of the libraries were quite different. Still nine specific CRESS-DNA virus-like sequences were found with reads detected in both the deep sediment core layers and the quagga mussels. Cs137 dating results of the offshore sediment cores showed two distinct layers, the top 6 cm sediment layer after 1952 and the second before 1952. Both of my sediment core metavirome libraries were from before 1952 indicating that quagga mussel invaders are interacting with CRESS-DNA virus-like sequences likely historically present in the region. A specific CRESS-DNA virus-like sequence, Lake Michigan Quagga Mussel associated CRESS-DNA virus-like sequence 1241 (LMQMvls1241) was found to be abundant in only the quagga mussel metavirome libraries. Hence, I used qPCR to quantify the abundance of the virus-like sequence in quagga mussel samples. Quagga mussel samples from across the central Lake Michigan benthos and Muskegon Lake were compared with samples obtained in the Rybinsk Reservoir in Russia. LMQMvls1241 was not present in samples from the Rybinsk Reservoir in Russia and found only in quagga mussels in the offshore benthos of central Lake Michigan suggesting that it did not originate in the quagga mussels native region (Europe) and are likely part of the Lake Michigan benthic viral consortium. This study shows that quagga mussels are interacting with CRESS-DNA viruses that have been historically present in the Lake Michigan benthos and raises interesting questions about what invertebrate associated CRESS-DNA viruses are infecting.

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