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 2019

Document Type


Degree Name

Bachelor of Science (BS)


Department of Biology


M. Rockwell Parker


Pheromones are utilized by many species as sexual signals driving mate choice, and pheromone production in vertebrates hinges on sex hormone action. Female red-sided garter snakes (Thamnophis sirtalis parietalis) produce a skin-based sex pheromone used by males for mate detection and selection. Estradiol is necessary for pheromone production, yet the specific mechanisms within the skin are unknown. Central to this is the metabolism of testosterone to estradiol via the enzyme aromatase. It is hypothesized that female garter snakes synthesize estradiol locally in the skin and maintain pheromone production via tissue-specific regulation of aromatase. Further, I hypothesize that female attractiveness, and therefore pheromone production, can be inhibited by targeting aromatase activity. Using qPCR, I detected sexually dimorphic expression of aromatase in the skin (3.5-fold increase in females; t20=2.30,P=0.032). To inhibit aromatase activity, I treated females with a known aromatase inhibitor (fadrozole; FAD). Females received either FAD injections (100 μg/mL; n=10 females) or control injections (saline; SHAM; n=10) three times a week for six months. Pheromones were isolated from snake shed skins, and blood plasma was collected to determine circulating estradiol. In the den the next spring in Manitoba, Canada, SHAM and FAD females were differentially attractive based on bioassays with wild males. FAD females attracted ~50% less courtship than wild females in two different bioassays (competition: F2,22=6.54, P=0.007; mating ball test: F2,24=22.454, P=<0.001). Collectively, my results are the first to indicate a key role for tissue-specific aromatase expression invertebrate pheromone production



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