Date of Award

Summer 2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Ocean Science and Engineering

Committee Chair

Robert J. Griffitt

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Leila Hamdan

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Eric Saillant

Committee Member 3 School

Ocean Science and Engineering

Committee Member 4

Kristine Willett

Abstract

The 2010 Deepwater Horizon (DWH) oil spill resulted in the oiling of approximately 2100 km of shoreline. During that time, resident organisms had to contend with the effects of multiple contaminants and suboptimal environmental conditions. This research examines the molecular effects of DWH oil spill contaminants in estuarine fish (CyprinodonvariegatusandFundulusgrandis) across multiple life stages, contaminant concentrations, and in conjunction with environmental stressors.

Our results indicate that:

1. Oil elicits substantial transcriptional effects across life stages in C. variegatus. In adults, exposure to low concentrations of oil and dispersant results in transcriptional effects related to immunity, circulation processes, and DNA replication and repair. In early life-stage C. variegatus, oil exposure elicits different effects across developmental windows. Embryos mount a muted transcriptional response to oil, while larval stages mount a larger response dominated by dysregulation of transcription related to cholesterol biosynthesis, cardiac development, and immunity. In particular, the magnitude of transcriptional response in larval stages suggests examination of larvae may provide the most sensitive assessment of oil spill impacts.

2. Oil elicits differing transcriptional effects in ecologically similar species. We compared oil-induced transcription in larval C. variegatusand F. grandis and found distinct gene expression patterns in the two species, including opposing expression of genes involved in cholesterol biosynthesis. These results suggest that nuanced differences in molecular effects exist among fish, and should be considered when predicting the ecosystem-level effects of oil contamination.

3. Oil elicits altered DNA methylation patterns in larval C. variegatus. We found that oil exposure resulted in altered methylation at several genomic loci, and that simultaneous exposure to oil and hypoxia results in much greater effects to methylation than oil alone. We also determined that differentially methylated loci were correlated with differentially expressed genes, suggesting that altered methylation influences transcriptional responses following oil and hypoxia exposure.

Overall, these results suggest that the sub-lethal impacts of oil spill contaminants constitute a substantial insult to cellular and molecular functions in estuarine fish, and imply that effects to fish health following oil spills could be more widespread and persistent than previously thought.

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