Studying the physiology of declining Diporeia populations in the Laurentian Great Lakes using metabolomics

Suman Maity, Purdue University

Abstract

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 and production of essential amino acids were enhanced in diatom fed Diporeia. Our results have also shown that quagga exposure causes an elevated stress response in Diporeia especially for Lake Michigan organisms, suggesting lake-specific adaptive mechanisms for Diporeia in the Great Lakes. PCB exposure resulted in elevated cysteine and phospholipid metabolism and activation of AhR mediated pathways. Using multivariate analysis, these results were then compared to metabolite profiles from Diporeia (n = 148) collected from different lakes (Cayuga, Huron, Michigan, Ontario and Superior), years (2008–2009) seasons (fall and spring), and population histories (“stable” and “declining”). Amino acid (histidine and tryptophan) and lipid (sphingolipid and phospholipid) metabolism was primarily affected in declining populations. Overall, phospholipid metabolism was primarily impacted in both laboratory and field studies. Based on the analyses of field and experimental samples, it also appears that the presence of dreissenids elicits varied physiological response in Diporeia populations across lakes and availability of food also plays an important role controlling such changes in declining Diporeia population. The next step should involve the development of a cumulative health index based on a selected number of metabolites to be used for assessment of overall health status of Diporeia across Great Lakes.

Degree

Ph.D.

Advisors

Sepulveda, Purdue University.

Subject Area

Bioinformatics|Environmental science|Aquatic sciences

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