Population Structure and Mating Dynamics in the Social Amoeba Dictyostelium discoideum

Successfully investigating the evolution and maintenance of sex and mating systems can often have as much to do with choosing the right study system as it has to do with asking the right questions. Dictyostelium discoideum has long been the focus of researchers interested in understanding a number of biological processes, such as motility, chemotaxis and development. More recently, attentions have shifted to include questions about the evolution of social and sexual interactions both within and between species. The D. discoideum life cycles, both asexual and sexual, are uniquely social, each requiring a costly sacrificial act. This offers an ideal system for exploring questions about kin recognition, conflict, and the evolution of multicellularity, as well as the evolution of differential sexual investment and mating types. This dissertation focused on understanding the phylogenetic and geographical relationships between clones in D. discoideum and identifying the social and selective pressures that shape its mating system. I introduce this mating system in Chapter 1. In Chapter 2, I investigated genetic variation and population structure in D. discoideum to identify possible factors that could affect interactions between clones. I used DNA sequence data and phylogenetic techniques to show that though D. discoideum clones form a monophyletic group, there is evidence of genetic differentiation among locations (FST = 0.242, P = 0.011), suggesting geographic or other barriers limit gene flow between populations. In chapter 3, I again looked for population structure, this time concentrating on gamete size and sex ratio, to understand selective pressures maintaining multiple mating types in D. discoideum. Evidence suggests that both balancing selection and drift are likely acting on the D. discoideum mating system. I found no differences in gamete size across the three mating types and also no genetic differentiation across three wild populations at the mating type locus. However, I found that mating type frequency varied across these populations, likely due to drift. Chapter 4 focused on understanding the social dynamics of mating in D. discoideum. During macrocyst formation, two cells of complementary mating types fuse to form a zygote. This zygote then consumes hundreds of surrounding amoebae, likely clones of the original two cells, for use as protection and food. I varied the frequencies at which two clones of differing mating types interacted to investigate the possibility that one mating type cheats another by differentially contributing to the cannibalized cells. Contrary to previous claims that mating type I induces mating type II, coercing it to contribute disproportionately more of these cannibalized cells during macrocyst production, I found that these cells are likely contributed relative to their frequency in the population, regardless of mating type. However, I did find evidence for differential contribution to macrocyst production between some pairs of clones, suggesting that cheating can happen between partners during sex, but is rare and clone-specific. Overall, these studies looked for evidence of underlying population structure in D. discoideum that could impact our understanding of social and sexual interactions in this species. I also applied questions about the maintenance of sex usually only asked in two-sex systems to the unique social sexual interactions within D. discoideum in order to expand the understanding of how mating systems evolve and are maintained in nature. I developed and used new tools and techniques for observing the processes important to understanding this unique system and identified genetic and social factors that could impact how individuals interact during both the asexual and sexual life cycles

The Role of Compensation in Nicotine Reduction.

The available research on switching from normal nicotine to very low nicotine content cigarettes shows minimal evidence of compensatory smoking. Mathematical estimations suggest that substantial compensation after switching to very low nicotine cigarettes would be impossible. It is likely that smokers who are unable to tolerate the extent of proposed nicotine reduction would switch to other sources of nicotine, rather than try to compensate by smoking more very low nicotine content cigarettes more intensely

Mobilities, moorings and boundary marking in developing semantic technologies in educational practices

While much attention has been given to the changing spaces of education introduced by new technologies, the impact of spatial theory on the discussion of such education is less well developed. Drawing upon empirical evidence from the Ensemble research project, this article examines spatially some of the possibilities and constraints that arise in the introduction of semantic technologies into case-based learning in higher education. While the affordances of the semantic web provide a technological basis for the development of flexible tools and associated pedagogies in ways that could enhance case-based learning, there are many tensions in this process. In this article, we draw upon certain aspects of spatial theory to examine the ways in which the mobilities and openings made possible by the introduction of semantic technologies also entail mooring and boundary marking in order to give the technologies specifically educational purposes. We suggest how educational practices can be considered theoretically as spatial orderings and some of the implications

Carbon and nitrogen substrate utilization by archival Salmonella typhimurium LT2 cells

BACKGROUND: A collection of over 20,000 Salmonella typhimurium LT2 mutants, sealed for four decades in agar stabs, is a unique resource for study of genetic and evolutionary changes. Previously, we reported extensive diversity among descendants including diversity in RpoS and catalase synthesis, diversity in genome size, protein content, and reversion from auxotrophy to prototrophy. RESULTS: Extensive and variable losses and a few gains of catabolic functions were observed by this standardized method. Thus, 95 catabolic reactions were scored in each of three plates in wells containing specific carbon and nitrogen substrates. CONCLUSION: While the phenotype microarray did not reveal a distinct pattern of mutation among the archival isolates, the data did confirm that various isolates have used multiple strategies to survive in the archival environment. Data from the MacConkey plates verified the changes in carbohydrate metabolism observed in the Biolog™ system

Retinol improves bovine embryonic development in vitro

Retinoids are recognized as important regulators of vertebrate development, cell differentiation, and tissue function. Previous studies, performed both in vivo and in vitro, indicate that retinoids influence several reproductive events, including follicular development, oocyte maturation and early embryonic development. The present study evaluated in vitro effects of retinol addition to media containing maturing bovine oocytes and developing embryos in both a low oxygen atmosphere (7%) and under atmospheric oxygen conditions (20%). In the first experiment, abbatoir collected bovine oocytes were matured in the presence or absence of varying concentrations of retinol. After a 22–24 hour maturation period the oocytes were fertilized, denuded 18 hours later and cultured in a modified synthetic oviductal fluid (mSOF) in a humidified atmosphere at 38.5 degrees C, 5% CO2, 7% O2 and 88% N2. Cleavage rates did not differ among control and retinol-treated oocytes in all three experiments. Addition of 5 micromolar retinol to the maturation medium (IVM) tended (p < 0.07) to increase blastocyst formation (blastocyst/putative zygote; 26.1% +/- 2.2%) compared to the controls (21.9% +/- 1.9%). Further analysis revealed when blastocyst development rates fell below 20% in the control groups, 5 micromolar retinol treatment dramatically improved embryonic development, measured by blastocyst/putative zygote rate (14.4 +/- 2.1 vs 23.7 +/- 2.5; p < 0.02). The 5 micomolar retinol treatment also enhanced the blastocyst/cleaved rate by nearly 10% (23.7% vs 34.6%; p < 0.02). In the second and third experiments addition of 5 micromolar retinol to the embryo culture medium (IVC) under low oxygen conditions did not significantly improve cleavage or blastocyst rates, but 5 micromolar retinol significantly increased blastocyst development under 20% O2 conditions (p < 0.001). These studies demonstrate that supplementation of 5 micromolar retinol to the maturation medium may improve embryonic development of bovine oocytes indicated by their increased blastocyst rate. A significant improvement in the blastocyst development with the 5 micromolar retinol treatment under atmospheric conditions suggests a beneficial antioxidant effect during embryo culture

Sex ratio and gamete size across eastern North America in Dictyostelium discoideum, a social amoeba with three sexes

Theory indicates that numbers of mating types should tend towards infinity or remain at two. The social amoeba, Dictyostelium discoideum, however, has three mating types. It is therefore a mystery how this species has broken the threshold of two mating types, but has not increased towards a much higher number. Frequency-dependent selection on rare types in combination with isogamy, a form of reproduction involving gametes similar in size, could explain the evolution of multiple mating types in this system. Other factors, such as drift, may be preventing the evolution of more than three. We first looked for evidence of isogamy by measuring gamete size associated with each type. We found no evidence of size dissimilarities between gametes. We then looked for evidence of balancing selection, by examining mating type distributions in natural populations and comparing genetic differentiation at the mating type locus to that at more neutral loci. We found that mating type frequency varied among the three populations we examined, with only one of the three showing an even sex ratio, which does not support balancing selection. However, we found more population structure at neutral loci than the mating type locus, suggesting that the three mating types are indeed maintained at intermediate frequencies by balancing selection. Overall, the data are consistent with balancing selection acting on D. discoideum mating types, but with a sufficiently weak rare sex advantage to allow for drift, a potential explanation for why these amoebae have only three mating types

A Critical Role for OX40 in T Cell–mediated Immunopathology during Lung Viral Infection

Respiratory infections are the third leading cause of death worldwide. Illness is caused by pathogen replication and disruption of airway homeostasis by excessive expansion of cell numbers. One strategy to prevent lung immune–mediated damage involves reducing the cellular burden. To date, antiinflammatory strategies have affected both antigen-specific and naive immune repertoires. Here we report a novel form of immune intervention that specifically targets recently activated T cells alone. OX40 (CD134) is absent on naive T cells but up-regulated 1–2 d after antigen activation. OX40–immunoglobulin fusion proteins block the interaction of OX40 with its ligand on antigen-presenting cells and eliminate weight loss and cachexia without preventing virus clearance. Reduced proliferation and enhanced apoptosis of lung cells accompanied the improved clinical phenotype. Manipulation of this late costimulatory pathway has clear therapeutic potential for the treatment of dysregulated lung immune responses

Using sunn hemp as a cover crop in Oklahoma

The Oklahoma Cooperative Extension Service periodically issues revisions to its publications. The most current edition is made available. For access to an earlier edition, if available for this title, please contact the Oklahoma State University Library Archives by email at [email protected] or by phone at 405-744-6311

Crossover to the KPZ equation

We characterize the crossover regime to the KPZ equation for a class of one-dimensional weakly asymmetric exclusion processes. The crossover depends on the strength asymmetry $an^{2-\gamma}$ ($a,\gamma>0$) and it occurs at $\gamma=1/2$. We show that the density field is a solution of an Ornstein-Uhlenbeck equation if $\gamma\in(1/2,1]$, while for $\gamma=1/2$ it is an energy solution of the KPZ equation. The corresponding crossover for the current of particles is readily obtained.Comment: Published by Annales Henri Poincare Volume 13, Number 4 (2012), 813-82