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Thesis Abstract – Hernandez (2015)


The Effects of Urbanization on Circulating Testosterone Levels in Male Sceloporus occidentalis across Urban and Protected Areas in the Los Angeles Basin

Author and college:

Jessica Hernandez, Pomona College


May 2015


Bachelor of Arts in Biology


Kristine Kaiser, Department of Biology, Pomona College


Urbanization is a ubiquitous, rapidly occurring phenomenon responsible for adversely disturbing the environment and causing undue stress upon animals in the surrounding habitat. A common detrimental effect of prolonged stress on an animal is the suppression of behavioral and physiological reproductive processes. Indeed, stress hormones such as corticosterone (CORT) can chronically inhibit reproductive hormones such as testosterone (T) in most stress-inducing conditions. T is instrumental in stimulating energy expenditure during mating season, increasing aggressive behaviors, and activating courtship (Dunlap & Schall, 1995). Plasma T was collected from 76 male Western fence lizards (Sceloporus occidentalis) between May and August 2014 from urban, intermediate, and protected sampling sites located across the Los Angeles basin. Urban areas consisted of human-dominated socioecological ecosystems, while protected areas were locations deemed legally preserved/conserved due to ecological, natural, or cultural qualities. Intermediate areas referred to sites with a level of disturbance in-between that of urban and protected areas. To test the hypothesis that urbanization affected circulating plasma concentrations of T in male Western fence lizards, I performed competitive enzyme-linked immunoassays on collected lizard plasma to analyze circulating T levels in males found across an urban-protected gradient. I found that (1) circulating T levels were significantly higher in intermediate sites compared to urban and protected sites and (2) circulating T levels between urban and protected sites were not significantly different. Consequently, I argue that these findings provide evidence that males in the intermediate site are being exposed to unique stressors, in comparison to males in the other two sites. Also, male lizards in urban sites may have found ways to successfully adapt to the stressors inherent in an urban environment. While this system is apparently complex and multifaceted, studies such as this one will allow us to better comprehend how environmental stressors affect hormones, which will ultimately enable us to understand how endocrine modulation is carried out in lizards.

For more information:

Contact Wallace Meyer – Wallace.Meyer@Pomona.edu

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