Term of Award

Fall 2018

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Biology

Committee Chair

Christian Cox

Committee Member 1

Christine Bedore

Committee Member 2

John Schenk

Abstract

One prominent form of phenotypic diversity in nature is the dramatic difference between males and females within a single species. A central genetic obstacle which must be overcome is that two distinct phenotypes must be produced from a single, shared genome. One genetic mechanism that is of particular import that would allow sexes to overcome the limitation of a shared genome is sex-specific regulation of gene expression. Although sex-biased gene expression is generally predicted to increase over ontogeny as male and female phenotypes diverge, this pattern should be most pronounced in tissues that contribute to the most extreme aspects of sexual dimorphism. However, few studies have simultaneously examined multiple tissues throughout development to quantify sex-biased gene expression, which is crucial as sexual dimorphism occurs as a complex developmental process and sex-biased gene expression changes over time and differs among various tissues. We used the brown anole (Anolis sagrei), a lizard that exhibits extreme sexual size dimorphism, to examine sex-, age-, and tissue-specificity of gene expression. Using high-throughput RNA-Seq, we analyzed liver, muscle, and brain transcriptomes at one, four, eight, and twelve months of age. We predicted that (1) sex-biased gene expression would increase during ontogeny as phenotypes diverge between the sexes, (2) ontogenetic increases in sex-biased expression would differ among tissues because of different contributions to sexual dimorphism, and (3) growth-regulatory gene networks would be more sex-biased in liver and muscle than the brain as key contributors to extreme size dimorphism. We also predicted that sex-biased expression of upstream components of growth regulatory (e.g., hormones) networks in the liver would be higher compared to the muscle where there would be higher sex-biased expression of downstream components (e.g., hormone receptors and downstream effectors) in muscle. We determined that sex-biased gene expression increased during development, but that the trajectory of sex-biased expression varied between tissues. The liver had the greatest number of sex-biased growth genes, but the muscle had the greatest divergence of growth gene expression. We also found that while sex-biased expression of growth genes increased sharply during development in the liver and muscle, the brain showed no sex-bias in any growth gene at any point. Our results confirm that sex-biased gene expression increases throughout ontogeny, but also demonstrate tissue-specific trajectories. Our results also suggest that different components of growth-regulatory networks are activated in different tissues. More broadly, our work implies that sex-biased gene expression across the whole transcriptome and within specific regulatory pathways produces sexually dimorphic phenotypes.

Research Data and Supplementary Material

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