Melatonin is a naturally occurring hormone that is involved in the regulation of seasonal behaviors in a variety of species. Specifically, high levels of melatonin are associated with short photoperiods, which often coincide with the non-breeding season in most animals, meaning that melatonin may have an inhibitory role in regulating seasonal reproduction. To exert effects on different target tissues, melatonin must bind to its receptors (MT1 and MT2). Like other seasonally breeding animals, green anole lizards (Anolis carolinensis), have large, active gonads, increased levels of testosterone and estradiol, and increased reproductive behaviors during the breeding season compared to the non-breeding season. Previous studies have examined melatonin’s role in the transition between breeding and non-breeding states, but it is unclear how melatonin’s receptors change seasonally in brains and gonads. Additionally, it is unclear if melatonin treatment during the breeding season influences hormone levels or reproductive behaviors. In Experiment 1, we measured MT1 and MT2 mRNA expression in the brains and gonads of unmanipulated male and female anoles between breeding and non-breeding seasons. We found that MT1 mRNA expression was significantly higher in the male brain during the breeding season compared to the non-breeding season, and in general, MT1 mRNA levels were higher compared to MT2. This result suggests that melatonin may regulate seasonal reproduction primarily through MT1 in the brain, and higher levels during the breeding season may compensate for low seasonal levels of melatonin. In Experiment 2, males and females were treated with a subcutaneous pellet containing either melatonin or a blank control for 10 weeks during the breeding season. In males, melatonin treatment increased testosterone levels and decreased the latency to reproductive behavior. This suggests that rather than inhibiting reproduction, continuous high doses of melatonin stimulate reproductive characteristics during the breeding season, although the exact mechanism responsible for this action remains unclear. Additionally, female reproduction was not influenced by melatonin treatment, meaning that other factors beyond melatonin may regulate female reproduction. Our findings support the role of melatonin in modulating seasonal reproduction, but more work is needed to determine the exact mechanisms behind melatonin’s stimulatory effect in males.


Rachel Cohen

Committee Member

Michael Minicozzi

Committee Member

Keenan Hartert

Date of Degree




Document Type



Master of Science (MS)

Program of Study

Master of Science


Biological Sciences


Science, Engineering and Technology

Available for download on Saturday, March 21, 2026

Included in

Biology Commons



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