Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on January 5, 2010. Major professor: David Pilliod, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Biology." "December 2009." Includes bibliographical references. Also available on microfiche.

Toads were raised in the laboratory from the egg stage through three weeks after foreleg emergence. Three to six toads were preserved from each of ten stages of development between stage XX (foreleg emergence) and three weeks after stage XX. The specimens were cleared and stained by the alizarin technique, examined under a binocular dissecting microscope, and the skull bones drawn freehand.At stage XX ossification had begun in the frontoparietals, parasphenoid, premaxillae, septomaxillae, prootics, and exoccipitals. By one day after stage XX the squamosals, dentaries, and angulosplenials had appeared; by two days, the nasals and maxillae. By three days, two of four specimens possessed two ossification centers of each titerygoid bone. At three weeks the beginnings of the hyoid apparatus were apparent.Comparisons were made to the ossification of skull bones reported in the literature for Pseudacris triseriata and Rana pipiens. / Department of Biology

Observation of some of the phenomena of tolerance to soluble protein antigens and allogeneic tissue transplants in Xenopus laevis has formed the framework of the present study. The method of larval induction of high-zone tolerance used in this laboratory has been confirmed and further analysed. Larvae treated with high doses of Human-γ-globulin (HGG) were unable to produce anti-HGG antibody after challenge. The proliferative response demonstrated in the spleens of tolerant toadlets 21 days after challenge was, however, of similar magnitude to that in normally responding animals. Adoptive transfer of high-zone tolerance specific to HGG was demonstrated by intravenous inoculation of tolerant histocompatible splenocytes simultaneously with an antigenic challenge via the dorsal lymph sac. This is indicative of the active involvement of a suppressor T-cell population. The induction of high-zone tolerance in X. laevis results in changes in spleen cell populations as demonstrated by buoyant density gradient separation. Spleen cell sub-populations taken from the separated layers were not, however, effective in the adoptive transfer of tolerance. A normal lymphocyte transfer reaction was observed in X. laevis to show a number of characteristics seen in the mammalian reaction. The use of mitomycin-C treated donor cells and early thymectomized hosts has demonstrated that the phenomenon is composed of donor and host components which are largely distinct from each other. Implantation of allogeneic larval spleens resulted in the induction of transplantation tolerance or impaired rejection in a significant proportion of skin grafted toadlets in which both the donor and host larvae were up to and including stage 51 at the time of transplantation. The implication of these results is that immunomaturity of the donor and host is important in the induction of transplantation tolerance but that other factors must also be involved.

"Professional paper presented in partial fulfillment of the requirements for the degree of Master of Science in Wildlife Biology, the University of Montana, Missoula, MT, spring 2007." / Title from PDF title page (viewed Aug. 20, 2007). Includes bibliographical references (p. 15-20).

No description available.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 149-168). Also available on the World Wide Web.

One of the major limitations on research into the control of eukaryotic DNA replication has been the lack of any cell-free system that initiates DNA replication in vitro. The first part of the disseration describes the establishment of a eukaryotic system, derived from the activated eggs of the South African clawed toad, Xenopus laevis, that efficiently initiates and completes DNA replication in vitro. Using a variety of biochemical techniques I show that DNA added to the extract in the form of sperm nuclei is efficiently replicated over a period of 4 - 6 hours. Replication of nuclear DNA represents a single round of semiconservative, semidiscon-tinuous replication. The extract will also replicate naked DNA incubated in it, regardless of sequence, though less efficiently than nuclear templates. This is probably related to the unusual ability of the egg extract to assemble apparently normal interphase nuclei from any DNA molecule incubated in it Evidence is presented that initiation, rather than chain elongation, is the rate-limiting step for replication in vitro. In this and in other ways the cell-free system behaves as though it were an early embryo blocked in a single cell cycle. The second part of the dissertation describes experiments that examine the control of DNA replication in the extract The first set of experiments suggest that on replication, DNA is marked in some way so that it can no longer act as a substrate for further initiation. This provides a mechanism by which the template DNA is replicated precisely once per incubation in vitro (or per cell cycle in vivo). The second set of experiments investigate the relationship between nuclear assembly and the initiation of DNA replication in vitro. A novel method for quantifying DNA replication in intact nuclei using the nucleotide analogue biotin-11-dUTP is described. This technique reveals that although they are in the common cytoplasm of the egg extract, different nuclei start to replicate at different times. Entry into S-phase is characterised by a burst of many synchronous or near-synchronous initiations within individual nuclei. This means that nuclei act as independent and integrated units of replication in the cell-free system, and suggests a fundamental role for nuclear assembly in controlling DNA replication in vitro.

No description available.

No description available.

The evolution of mating signals has long interested biologists because changes in mating signal production and/or reception can lead to reproductive isolation and speciation. Here, I examine the evolution of the male mating signal (the advertisement call) and the female preference for this call in the Western Toad, Bufo boreas. Call surveys and a morphological study for the occurrence of vocal sacs, which are necessary for producing these calls, reveal that only populations in the northeastern corner of this species’ range produce long, high-amplitude advertisement calls. This is the first study to report among-population variation in the presence of the major mating signal in any animal. Although populations vary in whether or not males call, phonotaxis tests demonstrate that female B. boreas in calling and non-calling populations have the preference for this call. Phylogenetic analyses indicate that the call was lost in the ancestor to modern B. boreas and then secondarily re-evolved in the ortheastern populations. Bufo boreas is one of many toad species that inhabits the Nearctic region. I use phylogenetic analyses of large and small subunit mitochondrial ribosomal DNA sequences to examine the phylogenetic relationships among Nearctic toad species and test previously proposed biogeographic hypotheses for the colonization history of the Nearctic region. This work indicates that the Nearctic Bufo are monophyletic and result from a single colonization event from the Neotropics. Further, fossil and paleogeographic data suggest that this colonization occurred prior to the formation of a contiguous land bridge between the Neotropic and Nearctic regions. Many of the individuals examined in the Nearctic toad study had previously been sequenced for the same gene region. A surprising number of errors were found in the earlier sequences and attributed to the method of sequence generation. In my final chapter, I review the causes and consequences of sequencing error and present a novel method that uses sequence conservation information to detect errors. This approach is exemplified with the unique dataset of replicated sequences, and resources for easily implementing this approach are made available on the Comparative RNA Web Site (http://www.rna.ccbb.utexas.edu/). / text