Influence of testosterone on male-male competition in the red-sided garter snake, Thamnophis sirtalis parietalis

Author

Isabella M. G. Bukovich, James Madison UniversityFollow

Creative Commons License

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

Date of Graduation

12-19-2020

Publish

yes

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Department of Biology

Advisor(s)

M. Rockwell Parker

Idelle A. Cooper

Roshna E. Wunderlich

Abstract

Female mimicry in the red-sided garter snake, Thamnophis sirtalis parietalis, is described in several well-studied evolutionary advantages, but an aspect that remains elusive is how reproductive traits are linked to the 3-fold higher circulating androgens in males with this phenotype. In this study, we implanted male garter snakes (n=15 per group) with either a blank implant (SHAM; control) or a T implant, the latter simulating the female mimic phenotype. Following simulated low-temperature dormancy, males were scored for courtship intensity over three days of behavioral trials with females housed in the same facility. Males were sacrificed, and sperm were collected from the ductus deferens for analysis of quantity and morphology. Increased testosterone (T) provides more substrate to activate sexual behavior in this species, thus I predict that males supplemented with T will have a competitive advantage by initiating courtship at a greater intensity or sustaining courtship behavior for longer than controls. I further predict T will promote spermatogenesis to manifest as higher sperm concentration and quality. For my results, T males exemplified greater courtship intensity via an immediate effect; courtship scores were higher 1-minute following trial initiation on day 3. Sperm count was marginally higher for T males, and the sperm head region may be smaller for T males, though no other region (midpiece, tail, total length) was affected. These findings provide evidence for formerly unknown added advantages of female mimicry in snakes via possibly enhanced courtship and sperm competitiveness.

Recommended Citation

Bukovich, Isabella M. G., "Influence of testosterone on male-male competition in the red-sided garter snake, Thamnophis sirtalis parietalis" (2020). Senior Honors Projects, 2020-current. 106.
https://commons.lib.jmu.edu/honors202029/106