Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 71-78). Also available via the Internet.

No description available.

Thesis (M.S.)--Western Washington University, 2010. / Includes bibliographical references (leaves 69-75). Also issued online.

Thesis (Ph. D.)--University of Oregon, 2001. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 121-147). Also available for download via the World Wide Web; free to University of Oregon users.

I evaluated possible constraints on the evolution of viviparity in the lizard genus Sceloporus by experimentally extending the length of egg retention past the normal time of oviposition for a number of oviparous species. Observations also included a representative of the genus Urosaurus, the sister genus to Sceloporus. I determined the effects of retention on embryonic development, hatchlings, and gravid females. Results indicated that the proximate constraints on longer retention times and viviparity are 1) embryonic development becomes arrested or severely retarded in utero, and 2) the ability to maintain gravidity past the normal time of oviposition is limited in some species. Observations on Urosaurus further showed that extended egg retention results in hatchlings with traits that are associated with lower fitness. I also tested the hypothesis that reproductive Sceloporus lower their body temperatures during activity because their normal body temperatures are detrimental to embryos. Observations on a viviparous species of Sceloporus indicated that the normal body temperature of the female was detrimental to embryonic development. This result is indicates that viviparity would be constrained in some squamate lineages if maternal body temperatures are too high for successful embryonic development. I also evaluated the hypothesis that the evolutionary transition from oviparity to viviparity involves a "reduction" of the eggshell concurrent with longer durations of egg retention. If this hypothesis is correct, then attributes of eggshells that should enhance exchange of respiratory gases (i.e., thickness, density, permeability to water vapor) would be correlated with the maximal developmental stage that embryos are able to attain in the oviducts (i.e., stage of developmental arrest). The results of this study indicated that these features of shells do not determine the stage at which development becomes arrested. Thus, the results do not support the hypothesis that shell reduction occurs concurrently with longer periods of egg retention. The results are consistent with the alternative hypothesis that reduction of the eggshell occurs after viviparity has evolved. / Ph. D.

Habitat preference of the eastern fence lizard, Sceloporus undulatus, was investigated in southwestern Virginia. Habitat features were measured at 158 lizard-centered plots and at paired random plots. Landscape-level variables, southerly aspect and mixed forest type, distinguished lizard-centered from random sites. Hatchlings were associated with relatively high temperature at perch height (23 °C), relatively high amounts (per 1- m2) of coarse woody debris (15%) and bare ground (15%), and relatively low amount of litter (34%). Adults and juveniles were associated with a relatively high number of rocks (22 per 0.01 hectare) and amount of coarse woody debris (9% per 1- m2). Habitat preferences were modeled with a Geographic Information System (GIS) using landscape-level variables and with logistic regression and Akaike's Information Criterion using site-level variables. The best-fitting site-level model for adults/juveniles included % CWD. The best-fitting model for hatchlings included % CWD and number of rocks, and the second best-fitting model also included % litter. Landscape (both classes) and site-level models (adult/juveniles only) were tested at 15 GIS-predicted "suitable" study areas and at 15 GIS-predicted "unsuitable" areas. Site-level models for hatchlings were tested with independent data collected at two study areas. Sixteen lizards were found at "suitable" areas and one at an "unsuitable" area; the GIS-based model was a good predictor of lizard presence at the landscape level. The best-fitting site-level models for adults/juveniles and hatchlings were poor predictors of lizard presence while the second best-fitting hatchling model was a good predictor of hatchling presence. / Master of Science

Rates and energy equivalents of consumption (C), egestion+ excretion (FU) , assimilation (A), respiration (R) and production (P) were measured in two groups of Sceloporus olivaceus: 1) a laboratory group acclimated at four seasonally encountered temperatures (15, 20, 25 and 30°C) ; and 2) four acclimatization groups collected at different seasons when ambient temperatures corresponded to 15, 20, 25 and 30°C.

Males of the Mexican lizard Sceloporus minor (Phrynosomatidae) exhibit striking variation in dorsal coloration, both within and among populations, which may have arisen by sexual selection. The possible significance of this trait was investigated through a combination of observational and experimental approaches. This research revealed that males in one population (La Manzana) in NW Hidalgo exhibit three discrete color morphs (blue, yellow, red) each characterized by morphological, physiological and behavioral differences. Furthermore, these morphs can be identified by an objective approach to color assessment (spectroradiometry). In addition, males in a second population (Escalerillas) from SE San Luis Potosí were also found to occur in at least two color morphs (yellow and red), suggesting that color polymorphism may be general in this species. The hypothesis of sensory exploitation by male contest competition was tested for S. minor from Escalerillas; however, no support for this hypothesis was found. Overall, results from this study are consistent with the hypothesis of alternative reproductive tactics in S. minor.

Thesis (Ph. D.)--University of Nevada, Reno, 2006. / "May 2006." Includes bibliographical references. Online version available on the World Wide Web.

We used light microscopy to study placental structure of the lizard Sceloporus mucronatus throughout 6 months of embryonic development. Three stages of placental development could be assigned to embryos based on the arrangement of the extraembryonic membranes. A highly vascular choriovitelline placenta was present in the embryonic hemisphere and a nonvascular bilaminar omphalopleure covered most of the abembryonic hemisphere of the egg during embryonic Stages 10-28. A chorioallantoic placenta replaced the choriovitelline placenta by embryonic Stage 29 and an omphaloplacenta covered the abembryonic hemisphere at this stage. The combination of these two placental types occurred in Stage 29-36 embryos. The final stage of placentation, embryonic Stages 37-40, was characterized by an omphalallantoic placenta in the abembryonic hemisphere and a chorioallantoic placenta in the embryonic hemisphere of the egg. The choriovitelline and chorioallantoic placentae are well vascularized, with closely apposed maternal and embryonic blood vessels. These structures are the most likely sites of respiratory exchange. In contrast, the omphaloplacenta and omphalallantoic placentae contain cuboidal or columnar epithelia and these structures may function in histotrophic exchange. Placentation of S. mucronatus is similar to that of predominantly lecithotrophic species in other squamate lineages suggesting that the evolution of this placental morphology is a response to similar factors and is independent of phylogeny.