Thesis (doctoral)--University of Tartu, 2006. / Thesis based on three papers.

Thesis (doctoral)--University of Tartu, 2006. / Thesis based on four papers.

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xiii, 143 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 113-120).

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

The study of protein polymorphism in natural populations has stimulated heated controversy over the effects of various evolutionary forces on the observed patterns of genetic variation. One viewpoint is that a majority of the mutations at a locus are selectively equivalent and that variations in gene frequencies in time and space are primarily a result of nonselective evolutionary forces. The opposing view is that most mutations have sufficient effect on individual fitness that variations in gene frequencies are adaptations resulting from the action of natural selection. I compared gene frequency distributions among various loci to assess the roles of selective and nonselective evolutionary forces in determining patterns of allozyme variation in populations of rodents. I used two versions of the Lewontin-Krakauer test on temporal variation in allozyme frequencies reported for populations of the prairie vole, Microtus ochrogaster. The tests revealed that the changes in gene frequency were homogeneous among loci which suggests that nonselective forces such as genetic drift and migration were the primary cause of gene frequency change within populations. I also compared the spatial gene frequency distributions reported for 17 species of rodents to assess which evolutionary factors account for the genetic differentiation of populations within each species. Most loci showed similar degrees of differentiation, a pattern expected if nonselective forces operated in population differentiation. I found a positive relationship between the amount of differentiation of populations and the magnitude of positive association among rare alleles. This result suggests an active role of genetic drift in population differentiation within rodent species. The analysis of allozyme distributions in populations of rodents indicates that nonselective evolutionary forces play a substantial role in determining patterns of genetic variation. According to Wright's Shifting Balance Theory, the random differentiation of populations may actually accelerate adaptive evolution, which may account for the rapid evolutionary rates found in rodents.

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Taurine transport in purified brush-border membranes from rodent kidney is concentrative and driven by the Na('+) gradient and transmembrane potential difference. The high-affinity, low-capacity carrier is specific for (beta)-amino compounds. / Inherited, strain-dependent influences on taurine reabsorption were investigated in the C3H/HeJ strain, a low excretor of taurine in urine and the C57Bl/6J strain, a high excretor. Although both strains transport taurine similarly at the luminal membrane, impaired exit at the baso-lateral membrane of renal epithelium in the hypertaurinuric strain results in increased intracellular levels of taurine and subsequent backflux into the urine. / The kidney is an important arbiter of taurine homeostasis. When animals are deprived of taurine, the kidney adapts by increasing taurine uptake at the renal brush-border membrane and in renal cortex slices; fractional excretion drops sharply. A change in plasma taurine may be the critical signal for adaptation.

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