Senior Honors Projects, 2010-2019

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Date of Graduation

Spring 2017

Document Type


Degree Name

Bachelor of Science (BS)


Department of Biology


M. Rockwell Parker

Ray A. Enke

Bisi T. Velayudhan


The production of many secondary sexual signals, including pheromones, is controlled by sex hormone action at the sites of signal synthesis. The red-garter snake (Thamnophis sirtalis parietalis) is an ideal vertebrate for studying the interaction between steroids and sexual signals: males exclusively rely on skin-based female pheromones during courtship, and pheromone composition is augmented by treatment with sex steroids (e.g., males produce female pheromone if implanted with estrogen). But how do steroid hormones promote pheromone expression at the molecular level in snake skin? Feminizing effects of estrogens on sexual signals are known to result from activation of estrogen receptors α (Esr1) and/or β (Esr2), while masculinizing effects of androgens arise from androgen receptor (AR) activation. We hypothesized that Esr1 and Esr2 are expressed in garter snake skin but their expression is sex-dependent with female skin expressing higher levels of Esrs. To test this, red-sided garter snakes (n=7 males, n=7 females) were collected in the spring mating season, and mRNAs from skin and control tissues (liver) were extracted and used to synthesize cDNAs. Primers were designed using the available T. sirtalis genome (NCBI) and tested in real-time PCR reactions. While both receptor types were expressed in male and female skin, Esr1 was more highly expressed in female skin. We thus attribute the feminizing effect of estrogen on pheromone phenotype in males to their lack of circulating estrogen and subsequently dormant Esrs.



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