Quantification of endocrine disrupting chemicals in central Texas rivers and associations with genomic variation in red shiners




Guzman, Alexis

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Over the past decade, chemical pollution has increased in freshwater systems, including increases in endocrine disrupting compounds. One of the most prevalent of these chemical pollutants is 17α-ethinylestradiol (EE2), a synthetic estrogen used for contraceptives. Exposure to EE2 under laboratory conditions has been demonstrated to alter reproduction, development, and behavior of aquatic organisms. Most water quality assessments, however, have detection thresholds that are substantially higher than most observed concentrations of EE2. Furthermore, detection thresholds are higher than biologically relevant concentrations of EE2 as understood from laboratory studies. In this study, I used a sensitive assay to quantify EE2 concentrations in water and red shiner fish, <i>Cyprinella lutrensis</i>, collected from five central Texas rivers. I detected EE2 in all rivers at concentrations that have been shown to cause adverse effects in aquatic organisms. The observed concentrations of EE2 in water and fish suggest that aquatic organisms in central Texas commonly experience non-trivial exposure to EE2. Additionally, given that EE2 can influence reproduction and disrupt development, EE2 exposure could represent a substantial selective pressure for aquatic organisms. I used a Genotype-Environment-Association (GEA) approach to ask whether genomic variation in red shiners was associated with variation in EE2 concentrations. For this, I generated 33,902 single nucleotide polymorphisms (SNPs) for 152 red shiners from 14 localities in five rivers. GEA analysis using Redundancy Analysis included EE2 concentrations in water and fish as predictors of genomic variation as well as other environmental predictors of water quality and patterns of land use in watersheds. Variance partitioning revealed significant proportions of genomic variation explained by my predictors and complex interactions among them. My results indicate that EE2 is not substantially associated with genotypic variation but represents a significant contaminant in central Texas rivers.



Population genomics, Genotype-Environment-Association


Guzman, A. V. (2022). <i>Quantification of endocrine disrupting chemicals in central Texas rivers and associations with genomic variation in red shiners</i> (Unpublished thesis). Texas State University, San Marcos, Texas.


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