Date Thesis Awarded

7-2012

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Paul D. Heideman

Committee Member

John D. Griffin

Committee Member

Margaret Somosi Saha

Committee Member

Jianjun Paul Tian

Abstract

Neuroendocrine mechanisms give rise to naturally occurring individual variation in life history traits on which natural selection acts. This study explores a possible neuroendocrine mechanism that gives rise to variation in photoperiod responsiveness. In this study, we use a colony of wild-caught P. leucopus at the College of William and Mary. We used two selection lines, one reproductively responsive to photoperiod, the other reproductively non-responsive to photoperiod. Previous research has shown a significant difference in the number of immunoreactive (IR) Gonadotropin Releasing Hormone (GnRH) neurons between photoperiod responsive and non-responsive lines. The photoperiod responsive line had significantly fewer IR-GnRH neurons than the photoperiod non-responsive line. Previous research indicates that the difference between selection lines arises from genetic variation, not photoperiod. GnRH is presumed to be regulated by kisspeptin, the gatekeeper of the hypothalamic-pituitary-gonadal axis. We tested the hypothesis that variation in the number of kisspeptin neurons may contribute to variation in photoperiod responsiveness. Immunocytochemistry specific to kisspeptin was performed on brain sections from the same individuals used in the GnRH study. IRkisspeptin neurons were counted and compared across selection lines and photoperiod treatments. We detected a significantly higher number of IR-kisspeptin neurons in the photoperiod non-responsive line and a correlation between number of IR-kisspeptin neurons and IR-GnRH neurons. However, we detected no significant difference in number of IR-kisspeptin neurons between photoperiod treatment groups. These results indicate the number of IR-kisspeptin neurons varies genetically in our population of mice. This variation may play a role in responsiveness to photoperiod.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Public Domain Dedication 1.0 License.

Comments

Thesis is part of Honors ETD pilot project, 2008-2013. Migrated from Dspace in 2016.

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