Arbuscular mycorrhizal fungi (AMF) are a group of root obligate symbionts that are part of the fungal sub-phylum Glomeromycotina, which provide water, nutrients, and pathogen protection to about 80% of land plants in exchange for their photosynthetic products. AMF thus act as “biofertilizers”, have a profound effect and influence on the biodiversity of plants, and play a major role in life on land. From an evolutionary point of view, AMF are a puzzling group of organisms, thought to have propagated for over 400 million years without sexual reproduction, a rarity among eukaryotes. However, this assumption is largely based on the absence of definitive observations of sexual reproduction through microscopic tools. One clue into the sexual activity of AMF is evidence of a dikaryotic-like genome organization in their multi-nucleated mycelium. The recent identification of multi-allelic mating-type loci (MAT locus) potentially places AMF among other heterothallic or bipolar species, who’s mating compatibility is determined by their MAT locus. The presence of a hidden sexual cycle in AMF is still a possibility, and recent findings on the meiotic gene content of AMF suggests an alternative narrative to how these fungi have escaped extinction for so long. Seven meiosis-specific genes (MSG) were found to exist in AMF, indicating that these fungi are likely undergoing a cryptic sexual cycle. The main goal of this research is to determine if/when MSG are expressed in an in-vitro model of AMF. To build onto this research, we established crossings between isolates with hypothetically compatible mating types, in order to determine if fusion of their hyphae can trigger the expression of MSG. Together, these experiments will assess expression at varying stages of the putative cycle of sexual reproduction and give further insight into the elusive sexual life of AMF.

No description available.

Genetic control of decapitation-induced fission in planaria is mediated by stimulator and inhibitor molecules. Resolution of the two factors was accomplished by filtration chromatography of whole planaria extract. The stimulator (M.W. 2500 to 3500) was purified with ion exchange chromatography and increases the multiple fission rate. The inhibitor (M.W. 20,000 to 50,000) is non-dialyzable, heat labile and is inactivated unless kept frozen. Storage at 4°C results in a loss of inhibitory capacity with a concomitant stimulator increase, suggesting a protein-stimulator complex as the inhibitor. In light of a demonstrated animal intercommunication system, the inhibitor-stimulator complex is hypothesized as part of a natural population control mechanism. The stimulator (long-acting) is released into the culture medium and induces an all or none response among other members of the population which are physiologically receptive. Fission inhibition (short-lived) is elicited only upon intimate animal contact and is possibly in the animal slime.

A study was made of the postulated fission-inhibiting substance located in the cephalic region of Dugesia dorotocephala. Rearing decapitated planaria in four different concentrations (25, 50, 75 or 100 ug/ml) of head or whole body extract resulted in a positive correlation between the inhibition of fission rate and the concentration of extract. The difference in inhibitory activity between the two types of extracts was three percent at maximum. The inhibitory substance was partially inactivated at 60° C. There was a direct correlation between the length of time that the extract was heated and the inactivation of inhibitor. The active substance was precipitable with ammonium sulfate. Fractionation of whole body extracts with a Sephadex G-200 column showed the presence of three peaks. The material from all three peaks exhibited inhibitory activity, possibly indicating the presence of more than one inhibitory substance. Fractionation procedures with DEAE anion exchange columns inactivated the inhibitory substance(s). The mechanism of action of the inhibitory substance(s) is not known. The animals must be exposed to the extract within 24 hours after decapitation in order for maximum inhibition to be obtained.

Chronic bioassays were conducted on the annelid Aeolosoma headleyi Beddard (l888) to determine the effects of heavy metals on asexual reproduction. Bioassays were conducted with the chloride and sulfate salts of zinc, copper, cadmium, cobalt, and nickel. Additionally, chromium, as potassium dichromate, was tested. Of these metals, only two, zinc chloride and copper sulfate, significantly stimulated reproduction at or below 0.01 ppm of the metal. All metals inhibited reproduction at high concentrations and none, except the two above, had any significant effect on reproduction at the sublethal concentrations tested. Hydrogen ion concentrations between 6 and 10 units had no effect on reproduction. The effects of the metals were not due to pH or osmotic effects. Subsequent studies were conducted with zinc chloride to determine its effect on zooid scissiparity. As zinc concentrations increase, the time for first zooid scissiparity decreased. Second bud formation was inhibited by zinc levels greater than 0.1 ppm. Normally the worm exhibits paratomy (release of zooid with a developed cephalic region). Above 7.0 ppm zinc, the worms also exhibit architomy where the cephalic region is not developed prior to scissiparity. / Master of Science

<p>This dissertation investigates the processes of hybridation, polyploidy, and apomixis and their roles in the evolution of myriopterid ferns. First, I examine patterns of hybridization in members of the Cheilanthes yavapensis complex using a suite of techiniques, ranging from molecules to morphology--including isozymes, spore measurements, and molecular phylogenetics based on chloroplast and nuclear DNA markers--to elucidate relationships in this notorious group of ferns. Second, I utilize the rules of traditional taxonomy set by the International Code of Botanical Nomenclature to recircucmscribe and resurrect the genus Myriopteris from within cheilanthoid ferns. This revised classification is bolstered by results from my molecular phylogenetic analysis of DNA sequence data in the subsequent chapter. Then, using morphological and cytological analyses, I examine the evolution of indument, leaf and rachis shape, vernation, chromosome number, and reproductive mode across the myriopterid tree. In my concluding chapter I develop microsatellite markers for the apomictic triploid, M. lindheiemeri, and explore whether premeiotic chromosome duplication facilitates the production of genetically distinct offspring in this otherwise asexual lineage.</p> / Dissertation

Le changement climatique et l’augmentation des températures globales perturbent l’abondance et la distribution de milliers d’organismes, aquatiques et terrestres, et certains écosystèmes sont particulièrement sensibles à ces changements environnementaux. L’augmentation de température est la principale menace au maintien des populations de coraux, véritables ingénieurs écologiques de ces écosystèmes. Bien que la recherche sur les récifs coralliens se soit d’abord attachée à l’étude des coraux adultes, de nombreuses informations manquent sur la reproduction sexuée et asexuée, et leur rôle dans la conservation et restauration récifale. Le premier axe de ma thèse s’est donc construit sur la réponse des jeunes stades de vie à l’augmentation de température, pour d’abord évaluer les modifications de leur performance et ensuite évaluer dans quelles mesures les jeunes stades seraient capables de s’acclimater à des conditions de températures plus élevées. Au travers de différentes expérimentations en laboratoire sur le genre Acropora, j’ai ainsi mis en évidence 1) une résistance thermique importante (+2-3°C au-dessus des températures ambiantes) des gamètes face à l’augmentation de température, 2) une résistance thermique différente entre spermatozoïdes et ovocytes: ovocytes < spermatozoïdes, 3) et la mise en évidence du rôle majeur de l’environnement dans lequel se rencontre les gamètes une fois libérés, sur la qualité et la quantité de la fécondation. Enfin, j’ai identifié les conditions optimales thermiques de pré-exposition des gamètes pour maximiser leur succès de fécondation. Bien qu’un intérêt croissant soit porté sur la reproduction sexuée ces dernières années, l’utilisation de la reproduction asexuée demeure la méthode la plus utilisée pour restaurer les récifs coralliens, plus connue sous le nom de bouturage. Ainsi le second axe de ma thèse a cherché à mettre en évidence la plasticité phénotypique des coraux en cultivant des boutures provenant de 3 espèces dans 3 environnements différents et en analysant leur taux de croissance, leur état de santé et leur survie. Cet axe a pu montrer qu’il existait des différences à plusieurs échelles, entre espèces, mais aussi au sein d’une même espèce. Mes travaux montrent qu’une sélection des individus basée sur l’étude de la plasticité phénotypique de certains traits d’histoires de vie comme la croissance ou l’état de santé dans des environnements variables permettrait d’améliorer l’efficacité de la restauration récifale. Ainsi le choix des individus au sein d’une même espèce afin de réaliser du bouturage (reproduction asexuée) et le conditionnement de la phase de vie gamètes (reproduction sexuée) peut permettre d’augmenter l’efficacité des méthodes de restaurations tout en nous donnant des informations nouvelles sur la biologie et la physiologie des coraux scléractiniaires face aux changements environnementaux. / Climate change and increasing temperature impact abundance and distribution of thousands of organisms, aquatic and terrestrial, and some ecosystems are particularly sensitive to these global changes. Increasing temperature is the principal threat for coral populations, which are ecological engineers of coral reef ecosystems. While research on coral reefs has first sought to study adult corals, data are still lacking on early life stages of corals. As sexual and asexual reproduction may play a key role in the conservation and restoration of coral reefs, my doctoral research aims to better understand changes on sexual and asexual reproduction in the face of rising temperature. The first axis of my Ph. D. was built on the response of early life stages to increasing temperature, in order to assess whether pre-exposure of early life may improve their ulterior performance. Among the different experiments performed on the genus Acropora, I highlighted 1) a high thermal tolerance (+2-3°C above ambient temperature) of gametes, 2) a higher sensibility of oocytes than sperm to rising temperature exposure, and 3) the pivotal role of gamete thermal history on fertilization output. Finally, I identified optimal pre-exposure conditions in order to maximize fertilization success. While an increasing interest in sexual reproduction was observed these last years, asexual reproduction and fragmentation still remain the main tool to restore damaged reefs. Thus, in the second axis of my doctoral project, I investigated the phenotypic plasticity of corals by growing 3 different species of corals across 3 different environments. Their growth rates, health status and survival probability were determined. Results from this axis showed that differences were observed at the interspecific and intraspecific levels. This work revealed that a selection based on phenotypic plasticity among different life-traits (growth rates and health status) and different environments should allow to increase coral reef restoration strategies. Hence the selection of individuals (asexual reproduction) in a species based on coral common garden experiment allow to identify individuals of interest to use as restoration biological materials. Additionally, thermal pre-conditioning of early life stages (sexual reproduction) is another way to increase efficiency of restoration measures in the face of rising temperature. My doctoral research provided new information regarding physiological and biological processes of scleractinian corals facing environmental changes and proposed new solutions for restorations based on sexual and/or asexual reproduction.

Estudos sobre evolução têm sido desenvolvidos desde a publicação dos trabalhos de Charles Darwin sobre a origem das espécies pela seleção natural em 1859. Durante o século XX grandes avanços foram obtidos com a utilização de modelagens matemáticas e computacionais, pois com exceção de algumas espécies que podem ter sua evolução analisada in vivo, o tempo necessário para aquisição de dados é enorme e por este motivo o enfoque computacional passou a representar uma ferramenta essencial. Nesta tese são apresentados os conceitos básicos para se entender o processo evolutivo de populações assexuadas como mutação, seleção e relevos adaptativos, bem como os resultados numéricos sobre sua evolução através do processo conhecido como catraca de Muller, que baseia-se na perda estocástica da classe de indivíduos mais adaptados da população através das mutações adquiridas ao longo de sua linhagem. Neste trabalho foram estudadas diversas dinâmicas, como a de populações que estão sujeitas à passagens seriais com gargalo, onde observamos que a velocidade da catraca na não pára devido aos altos valores de epistase, enquanto que para populações com tamanho variável (crescimento e decrescimento exponencial) a catraca pára durante o período de crescimento até a população atingir o limite permitido pelo meio-ambiente, sendo que a partir deste ponto ela se comporta como no modelo de infinitos sítios tradicional. Por último, são apresentados os resultados de populações que interagem entre si em uma dinâmica presa-predador, onde o comportamento da catraca pode ser entendido com base nas dinâmicas das populações descritas anteriormente. Um outro problema abordado nesta tese é o da utilização de medidas da topologia de árvores genealógicas para verificar a presença da seleção na evolução de uma população. Apesar dos comprimentos dos ramos das árvores apresentarem alterações quando comparados ao caso neutro, observamos que os testes estatísticos utilizados não são suficientes para inferir o efeito da seleção em populações reais. / Studies about evolution have been developed since Charles Darwin\'s publications about the Origin of species and Natural Selection in 1859. During the XX century major developments were achieved through mathematical and computational modeling, since only few number of species that their evolution can be studied in vivo, once that the time scale involed for data acquisition procedure is considerable, and for this reason the computational approach become an important tool in this study. In this thesis are presented the basic concepts to understand the process of evolution in a population as mutation, selection and adaptive landscapes, in addition some numerical results about the evolution of an asexual population using the process known as Muller\'s ratchet, that can be characterized by the stochastic loss of the most fitted class of individuals through mutations that are acquired in their lineages. During this work several dynamics were studied, likewise the populations under serial bottleneck passages, where we observed that the velocity of the ratchet never stops for high epistatic coefficients, while in population whose size can varies (increasing or decreasing exponentially) the ratchet halts during population\'s increasing until these individuals do not reach the maximum number permitted, and after this point this population behaves like the traditional infinite genome size model. At last, we show the results of populations that can interact between themselves in a predator-prey dynamics, where the behaviour of the ratchet can be understood in the previous dynamics. Another problem that was studied in this thesis is related with several topology measures of genealogical trees in order to verify the selection in a population evolution. Despite branch\'s length of the trees changed due to the selection, we could see that the statistical tests used do not be sufficient to infer the effect of selection under real populations.

Although genomes are perhaps the single most important element of living systems, why they feature such striking variation and how this variation is maintained within and across natural populations remains unclear. One of the most common and important means by which genomic variation is generated is ploidy elevation. While polyploidy has been implicated in the remarkably successful radiations of angiosperms, teleost fish, and amphibians, the phenotypic consequences of changes in ploidy level are poorly understood, especially in animals. I use a large, multi-year common garden experiment to identify potential life history costs and benefits of polyploidy and asexual reproduction, a trait often associated with polyploidy, in Potamopyrgus antipodarum. This snail is well suited for studying ploidy variation and sex because diploid sexuals and triploid and tetraploid asexuals frequently coexist, allowing us to use comparisons of sexuals to asexuals and triploid to tetraploid asexuals to study both the effects of ploidy elevation and sex. I detected a strong negative correlation between growth rate and time to maturity and found that sexual P. antipodarum grew and matured significantly more slowly than the polyploid asexuals. Sexual P. antipodarum were also more likely to die before achieving reproductive maturity than their asexual counterparts. By contrast, there were no apparent life history differences between triploid and tetraploid asexuals, indicating that direct phenotypic benefits of ploidy elevation are unlikely to explain the relatively rapid growth and maturation of asexuals. My results suggest that ploidy elevation does not inevitably confer phenotypic consequences, that reproductive mode influences life history trait expression, and that sexual P. antipodarum persist in many natural populations in spite of substantial life history disadvantages.

<p>What evolutionary processes and ecological patterns underlie the maintenance of asexual reproduction in natural populations? Although a vast body of literature offers theory to explain the existence of sexual and asexual reproduction, there has been little study of these forms of reproduction in the natural environment. In this dissertation I use a combination of field experiments, greenhouse studies, and genetic techniques to answer this question in the model plant system Boechera. </p><p>In Chapter 1, I review the utility of this system for studying ecological and evolutionary questions in general. Boechera offers an array of genetic and genomic tools, facilitated in part by a close evolutionary relationship with the model plant Arabidopsis thaliana, as well as undisturbed ecology and habitat that extends across much of North America. Additionally, the presence of apomixis (asexual reproduction via parthenogenetic formation of seeds) at the diploid level makes Boechera an ideal system for studying sex without the often-confounding factor of polyploidy; Boechera is one of very few plant groups in which this is possible. </p><p>In Chapter 2, I use a combination of microsatellite markers, flow cytometry, chromosome squashes, and morphological work to characterize apomixis, polyploidy, and species diversity in over 100 natural populations collected from central Idaho and western Montana. As in many other apomictic systems, I find that apomixis in Boechera is strongly linked to hybridization between species or between genetically divergent intraspecific lineages. I then explore associations between apomixis and ecological and topographical variables, as well as variables underlying differentiation between apomictic and sexual lineages. I find that ecological variables associated with apomixis are largely in congruence with the hypothesis of geographic parthenogenesis, and that geographic parthenogenesis is likely driven by the consequences of interspecific hybridization. We also find that apomixis is linked with disturbance and slope, with apomicts occurring in flatter locations than sexuals. </p><p>In Chapter 3, I use a large-scale field experiment comprising three years of data from two cohorts of sexual and asexual lineages to compare fitness between these two groups. I find that, despite herbivory levels that are much higher in apomicts than sexuals, apomictic fitness is consistently higher than sexual. Viability selection strongly favors apomicts, which results in a total fitness advantage for apomicts, despite variable fecundity selection. Selection varies in intensity between cohorts and among gardens. The results of a complementary greenhouse experiment show that the effects of herbivory differ by reproductive mode. Together, these experiments suggest that Red Queen dynamics may contribute to the coexistence of sex and asex in this group.</p><p>In Chapter 4, I use inter- and intraspecific F2 crosses to conduct a greenhouse study and a field experiment to explore the effects of hybridization and heterozygosity on fitness. I find that heterozygosity is favored in the field, with viability selection strongly favoring outcrossed over inbred lineages. However, hybridization results in lower survival, reproduction, and total fitness of interspecific F2 crosses, although hybrids that do reproduce produce more fruits than selfed parental lineages of both species, resulting in fecundity selection for hybrids. It is clear that the benefits of apomixis are due to hybridization, as hybrids are less fit overall. Evidence for both heterosis and outbreeding depression, dependent on lineage and on trait, are found in the field; these phenomena are not clearly associated with geographic distance between parental populations. Ongoing SNP genotyping will facilitate assessment of heterozygosity-fitness correlations as well as correlation of fitness and heterozygosity.</p> / Dissertation