Date of Award
2017
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biology
Abstract
Hormonal pleiotropy describes a suite of hormonally-linked traits. Such hormonal mediation may facilitate or constrain adaptive evolution of individual traits in the suite. Melanization, regulated in part by hormonal signals, can be tightly linked to non-color traits such as aggression, hormones, and immunity. While most studies examine within-population variation, I studied correlates of melanization, comparing both between- and within-population differences of adult male western fence lizards, Sceloporus occidentalis . I compared multiple high- and low-elevation populations in California, where populations are increasingly darker at higher elevations. I examined variation in 1) agonistic behavior of male lizards in response to staged territorial intrusions (STIs), 2) levels of the understudied peptide hormone, α-MSH, 3) both baseline- and post-captivity stress (1 hr) levels of two steroid hormones (testosterone, corticosterone), 4) mite loads, and 5) wound healing. Analysis of responses to STIs revealed that high-elevation males were more physically aggressive than males in lower-elevation populations. Populations did not differ in mean plasma α-MSH concentrations, but both testosterone and corticosterone levels differed significantly between populations, with higher aggression associated with lower testosterone. I also found darker (high-elevation) populations had higher mean mite loads than the less melanized (low-elevation) populations. Wound healing rate following a standardized wounding procedure, has faster for darker (high-elevation) males compared to lighter (low-elevation) males. Hormonal pleiotropy within the melanocortin system appears to not constrain phenotypic variation in Sceloporus lizards. I found differences in some traits across populations, but no association of individual variation in traits with individual variation in melanization. Physiological mechanisms contributing to within-population differences in melanization may be disassociated from mechanisms contributing to population-level differences. I discuss factors that could favor enhanced melanization at higher elevations. More studies comparing melanization, trait associations, and fitness consequences, both within and across populations, are warranted.
Recommended Citation
Seddon, Ryan, "Examining The Hormonal Pleiotropy Hypothesis: Malayization Along An Elevational Gradient Can Be Associated With Behavioral, Hormonal And Immunological Differences In Lizards" (2017). All-Inclusive List of Electronic Theses and Dissertations. 1937.
https://scholars.indianastate.edu/etds/1937