| Summary: | The holarctic amphipod Diporeia spp. used to be the most abundant benthic macroinvertebrate in the Laurentian Great Lakes. Diporeia serve as an important link between benthic and pelagic organisms within the Great Lakes by assimilating carbon from the benthic zone making it available to pelagic food webs. Due to their high lipid content, Diporeia are an ideal prey item for a number of fish species including lake whitefish ( Coregonus clupeaformis ) and slimy sculpin ( Cottus cognatus ). Since the 1990's, Diporeia have been extirpated from much of their former habitats. Their decline has coincided with the introduction and establishment of dreissenid mussels in the Great Lakes region. It has been hypothesized that Diporeia population declines are a result of decreased food availability from increasing competition with dreissenids for diatoms. There is additional evidence of remote effects of mussel pseudo-feces excreted by dreissenid colonies inducing toxic responses in Diporeia. In addition, persistent organic pollutants like polychlorinated biphenyls (PCBs), present in Great Lakes sediments, are known to elicit negative effects on Diporeia . However, stable Diporeia populations still persist in oligotrophic Lake Superior and co-exist with dreissenid colonies in Cayuga Lake. Our research has focused on elucidating the cause(s) of Diporeia decline using metabolomics as an exploratory tool. We conducted a series of laboratory experiments exposing Diporeia to multiple environmental factors (i.e., starvation, diatom diet, presence of quagga colonies, and exposure to PCBs). The physiological response elicited by each stressor was measured by evaluating changes in the metabolite expression pattern of Diporeia. Two separate instrumental platforms, two dimensional gas chromatography- and liquid chromatography both coupled with mass spectrometry, were utilized to study polar and non-polar metabolites, respectively. Starvation resulted in decreased phospholipid abundance and enhanced protein metabolism. Lipid biosynthesis ...
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