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dc.contributor.authorMathies, Tomen_US
dc.date.accessioned2014-03-14T20:22:45Z
dc.date.available2014-03-14T20:22:45Z
dc.date.issued1998-09-18en_US
dc.identifier.otheretd-9898-10551en_US
dc.identifier.urihttp://hdl.handle.net/10919/30774
dc.description.abstractI 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.en_US
dc.publisherVirginia Techen_US
dc.relation.haspartaaThesis.pdfen_US
dc.rightsI hereby grant to Virginia Tech or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University Libraries in all forms of media, now or hereafter known. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation.en_US
dc.subjectconstraintsen_US
dc.subjectevolutionen_US
dc.subjectviviparityen_US
dc.subjectSceloporusen_US
dc.subjectlizarden_US
dc.titleConstraints on the Evolution of Viviparity in the Lizard Genus Sceloporusen_US
dc.typeDissertationen_US
dc.contributor.departmentBiologyen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineBiologyen_US
dc.contributor.committeechairAndrews, Robin M.en_US
dc.contributor.committeememberHeath, Alan G.en_US
dc.contributor.committeememberSiegel, Paul B.en_US
dc.contributor.committeememberCranford, Jack A.en_US
dc.contributor.committeememberDenbow, Donald Michaelen_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-9898-10551/en_US
dc.date.sdate1998-09-18en_US
dc.date.rdate1999-10-15


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