In this study, mitochondrial transcript information from a recent EST project wasextended to obtain complete mitochondrial genome sequence for 5 tiger salamandercomplex species (Ambystoma mexicanum, A. t. tigrinum, A. andersoni, A. californiense,and A. dumerilii). For the first time, aspects of mitochondrial transcription in arepresentative amphibian are described, and then complete mitochondrial sequencedata are used to examine salamander phylogeny at both deep and shallow levels ofevolutionary divergence. The available mitochondrial ESTs for A. mexicanum (N=2481)and A. t. tigrinum (N=1205) provided 92% and 87% coverage of the mitochondrialgenome, respectively. Complete mitochondrial sequences for all species were rapidlyobtained by using long distance PCR and DNA sequencing. A number of genomestructural characteristics (base pair length, base composition, gene number, geneboundaries, codon usage) were highly similar among all species and to other distantlyrelated salamanders. Overall, mitochondrial transcription in Ambystoma approximatedthe pattern observed in other vertebrates. From the mapping of ESTs onto mtDNA it wasinferred that transcription occurs from both heavy and light strand promoters andcontinues around the entire length of the mtDNA, followed by post-transcriptionalprocessing. However, the observation of many short transcripts corresponding to rRNAgenes indicates that transcription may often terminate prematurely to bias transcriptionof rRNA genes; indeed an rRNA transcription termination signal sequence was observedimmediately following the 16S rRNA gene. Phylogenetic analyses of salamander familyrelationships consistently grouped Ambystomatidae in a clade containingCryptobranchidae and Hynobiidae, to the exclusion of Salamandridae. This robust resultsuggests a novel alternative hypothesis because previous studies have consistentlyidentified Ambystomatidae and Salamandridae as closely related taxa. Phylogeneticanalyses of tiger salamander complex species also produced robustly supported trees.The D-loop, used in previous molecular phylogenetic studies of the complex, was foundto contain a relatively low level of variation and we identified mitochondrial regions withhigher rates of molecular evolution that are more useful in resolving relationships amongspecies. Our results show the benefit of using complete mitochondrial genomeinformation in studies of recently and rapidly diverged taxa.

Thesis (Ph. D.)--Cornell University, 1902. / Cover title. "Reprinted from the Biological Bulletin, vol. IV, no. 2, December 1902."

No description available.

Tiger salamanders, and especially the Mexican axolotl (Ambystoma mexicanum), are important model organisms in biological research. This dissertation describes new genomic resources and scientific results that greatly extend the utility of tiger salamanders. With respect to new resources, this dissertation describes the development of expressed sequence tags and assembled contigs, a comparative genome map, a web-portal that makes genomic information freely available to the scientific community, and a computer program that compares structure features of organism genomes. With respect to new scientific results, this dissertation describes a quantitative trait locus that is associated with ecologically and evolutionarily relevant variation in developmental timing, the evolutionary history of the tiger salamander genome in relation to other vertebrate genomes, the likely origin of amniote sex chromosomes, and the identification of the Mexican axolotl sex-determining locus. This dissertation is concluded with a brief outline of future research directions that can extend from the works that are presented here.

This thesis has examined the food habits of two species of larval salamanders: Ambystoma tigrinum (Green), the Tiger Salamander, and Ambystoma tremblayi Comeau, Tremblay's Salamander, in east-central Indiana. Kinds of foods eaten by the individuals of each species were determined and a comparison of the data was made. In addition, the time of day at which feeding took place and preferences for specific food items were noted.Microcrustaceans were found to be the most important food item for the small larvae. As the larvae increased in size insects, crayfish, and other ambystomids became major food items. Daphnia was the most important food item for Ambystoma tigrinum larvae and Cyprts was the most important food item for Ambystoma tremblayi larvae. This was the only observable difference between the two species.Ball State UniversityMuncie, IN 47306

Ambystoma tigrinum undergoes an obligatory metamorphosis while A. mexicanum fails to metamorphose and exhibits paedomorphosis. While it is clear that salamander paedomorphosis is associated with genetic changes that delay developmental timing, it is not clear when and how these changes manifest during development. It is possible that paedomorphic and metamorphic larvae show equivalent patterns of developmental until late in the larval period, when brain regions become competent to stimulate the release of metamorphic hormones. To test this hypothesis, I compared gene expression patterns between the brains of A. mexicanum and A. t. tigrinum larvae. In support of the developmental equivalence hypothesis, 114 differentially expressed genes (DEGs) were identified in common between the species and all but 2 showed the same temporal pattern of expression. However, more DEGs were identified uniquely from each species. In particular, several genes that are associated with the hypothalamus-pituitaryinterrenal axis, which is implicated in metamorphic regulation in amphibians, exhibited significant expression differences between A. mexicanum and A. t. tigrinum larvae. The results show that metamorphic and paedomorphic modes of development are associated with different transcriptional programs in the brain and these programs diverge during early larval development.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

The ontogeny of the enzyme LDH has been studied in two species of amphibians (Amblystoma gracile and Rana aurora) as it provides a sensitive gauge of the state of differentiation of the organism, since the number and proportions of LDH isozymes present exhibit temporal and species specificity, thereby reflecting the degree of activity of the controlling genes. The presence of LDH in all stages of both species examined was established by assaying embryo homogenates for LDH activity, and the LDH was resolved into isozymic patterns by the methods of starch gel and disc electrophoresis. Specific enzyme activity for each developmental stage was correlated with the morphological events then occurring and the isozyme patterns obtained were discussed in terms of showing an increase in complexity during ontogeny and in terms of the current LDH isozyme hypothesis. A modified hypothesis was advanced to account for some of the experimental findings. / Science, Faculty of / Zoology, Department of / Graduate

This investigation considered the differentiation tendencies of specific anterior-posterior regions of the neural plate in an attempt to establish the regional differentiation capacity for Ambystoma gracile neuroepithelium. Presumptive neural tissues (hindbrain and trunk spinal-cord) were isolated from the embryo at the time of primary induction (stage 11) to post-neurulation (stage 19) and cultured in vitro alone or with combinations of axial mesoderm (notochord and somite). Prior to primary induction (stage 11), the isolated presumptive neuroepithelium formed only atypical epidermis. Immediately subsequent to this induction (stage 11) both regions (hindbrain and trunk cord) demonstrated unorganized neural histogenesis, while the formation of organized neural tissue appeared later (stage 12-14 isolates). By stage 15-16, the histogenesis of the isolated hindbrain resembled that of the control, whereas the isolated trunk cord only formed a neural tube. The presence of somite tissue enhanced hindbrain differentiation considerably; notochord was effective to a limited extent. The combined effect of both tissues on neurogenesis was greater than with somite alone. The addition of notochord to trunk spinal-cord enhanced histogenesis to a greater extent than either somite alone or the combination of notochord and somite. The trunk neural tissue, whether alone or in combination with mesoderm, never demonstrated normal spinal-cord morphology and seemed to develop independently of the tissue environment during the late neurula stages (16-19). The presence of inherent differentiation tendencies within the hindbrain and the trunk spinal-cord, as well as the possible role of the mesodermal tissue in conditioning the neural tissue microenvironment with metabolic precursors, is discussed. / Science, Faculty of / Zoology, Department of / Graduate