The Effects of Synthetic Estrogen on Sexual Selection and Hepatic Gene Expression Patterns in the Sex-Role-Reversed Gulf Pipefish
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Species in which sexual selection acts more strongly on females than on males provide interesting opportunities to study the evolution of sex roles and sex differences and the impact of exposure to endocrine disruptors. The sex-role-reversed Gulf pipefish (Syngnathus scovelli) is sexually dimorphic, and females possess dramatic secondary sexual traits while males are choosy. Experiments involving endocrine disruptors have previously illustrated that the secondary sexual traits in female pipefish are estrogen-regulated, but no studies before this dissertation had yet addressed the effects of endocrine disruptors on the strength of sexual selection or the hormonal regulation of a sexually dimorphic transcriptome in any sex-role-reversed taxon. When exposed to low, ecologically relevant concentrations of 17α-ethinylestradiol (EE2) of 2 ng/L, female pipefish had greater reproductive successes which resulted in an increase in sexual selection acting on exposed females. However, at minimally higher and still ecologically-relevant EE2 concentrations (5ng/L), male pipefish were unable to receive eggs or maintain their pregnancies, ceasing the reproduction of the exposed fishes. Understanding the evolutionary consequences of exposure to endocrine disruptors at several concentrations is important to help predict the effects that endocrine disruptors will have on the fecundity and sustainability of exposed natural populations. Using next-generation RNA-sequencing technology, I compared gene expression patterns in the livers of pipefish females, pregnant males, and non-pregnant males exposed to EE2 at ecologically relevant concentrations of 5ng/L. The results showed that the control Gulf pipefish liver transcriptomes showed sexually dimorphic patterns of gene expression, indicating that this sex-role-reversed pipefish species does not appear to have an endocrine reversal from the typical gene expression patterns found in the livers of most fishes with conventional sex roles. Estrogen exposure did cause feminization of gene expression patterns in the male liver transcriptome, with several of the EE2 responsive genes shown to have female-biased expression in control animals. These genes included several of the classic estrogen biomarkers, such as vitellogenin, choriogenin, and zona pellucida transcripts. Overall, exposure to synthetic estrogen has been shown to have a strong effect on selection, reproductive abilities, and hepatic gene expression levels in the sex-role-reversed Gulf pipefish.
Rose, Emily (2016). The Effects of Synthetic Estrogen on Sexual Selection and Hepatic Gene Expression Patterns in the Sex-Role-Reversed Gulf Pipefish. Doctoral dissertation, Texas A & M University. Available electronically from