L'identification de marqueurs génétiques liés à des gènes permet une exploration des éventuelles corrélations existant entre leur variabilité génétique et des pressions sélectives portant sur les gènes, aussi bien dans un contexte de populations expérimentales que naturelles. Chez le loup de mer (Dicentrarchus labrax), douze locus associés à des gènes - dont quatre associés aux gènes de l'hormone de croissance (GH), la somatolactine (SL) ou l'IGF-1- et huit locus anonymes ont servi à mener une étude multi-échelle de la différenciation génétique. La structure en trois bassins connue chez cette espèce a été confirmée mais les locus liés aux gènes ont montré une différenciation significativement plus forte que les locus anonymes et impliquant des barrières aux flux géniques nucléaires supérieures à celles admises jusqu'alors. A l'échelle mer-lagune, aucune image cohérente de différenciation génétique n'a pu être obtenue. Parallèlement, une expérience d'acclimatation à l'eau douce a été réalisée. Si les individus soumis à la désalure ont subi une mortalité importante, aucune différence génétique significative n'est observée entre les individus ayant survécu au traitement et ceux restés en eau de mer, excepté pour un locus EIF3E. Ces résultats ont révélé une composante familiale liée à l'expérimentation, mais les déterminismes génétiques sous-jacents restent obscurs. L'utilisation de marqueurs liés à des gènes a permis de révéler l'implication au moins indirecte de certains de ces gènes dans la mise en place d'une structuration génétique de l'espèce, mais également dans la réponse physiologique des individus à un stress environnemental pouvant être rencontré en conditions naturelles. / The identification of gene-linked genetic markers allows the exploration of potential correlations between their genetic variability and selective pressures acting on the genes in both natural and experimental populations. In Sea Bass (Dicentrarchus labrax), twelve gene-associated loci – four of them linked to Growth Hormone gene (GH), Somatolactin (SL) or IGF-1- and height anonymous loci were used in a multi-scale study of the genetic differentiation. The structure in three basins know in this species is well confirmed with gene-linked markers bearing a significantly higher differentiation than anonymous loci implying some stronger barriers to nuclear gene flow than admitted so far. At the open sea-lagoon scale, no coherent picture can be drawn from the different tests performed. A fresh water acclimation experiment was carried out in parallel. If numerous fishes in low-salt conditions died, the survivors are not genetically different from that maintained in salted water except for one locus EIF3E. These results can be partially explained by a family component but the genetic determinism is not elucidated yet. The use of gene-linked markers succeeded in revealing the involvement, at least indirect, of some of the genes in the edification of a genetic structure inside the species but also in the physiological response of the fishes to an environmental stress that can be encountered in natural conditions.

No description available.

No description available.

Sequences of the cytochrome b gene and genotypes from 11 polymorphic microsatellite loci were used to assess phylogeographic variation in ferruginous pygmy-owls (Glaucidium brasilianum) from Arizona, Mexico, and Texas. Analysis of mtDNA indicated that pygmy-owl populations in Arizona and Texas are unique, with no shared haplotypes. Populations from Sonora and Sinaloa, Mexico, were distinct from remaining populations in Mexico and grouped closest to haplotypes in Arizona. Nested clade analysis of mtDNA sequence data indicated past fragmentation separated pygmy-owls into two major groups: 1) Arizona, Sonora and Sinaloa, Mexico, and 2) southwestern (Nayarit and Michoacan), south-central (Oaxaca and Chiapas), and eastern Mexico, along the eastern slope of the Sierra Madre Oriental from Texas to Central America. In addition, analysis of mtDNA variation in several species of Glaucidium support the recommendation that populations of G. brasilianum from Mexico, Texas, and Arizona represent a phylogenetically distinct group from populations occurring in South America. The level of separation between the North and South Americanpopulations justifies granting species status (G. ridgwayi) to the North American population. Analysis of distance matrices derived from genotypes of 11 polymorphic microsatellite loci supports restricted gene flow between pygmy-owl populations in Arizona-Sonora and Sinaloa, and Texas-Tamaulipas and the remainder of states in Mexico. The Arizona-Sonora population showed signs of a recent genetic bottleneck, an observation supported by low population estimates for Arizona (13-117 individuals). Heterozygosity in Arizona, however, was equal to levels recorded throughout Mexico and Texas. Congruent patterns revealed by both mtDNA and nuclear DNA (microsatellites) indicate Arizona and Texas populations are distinct subspecies that require the design and implementation of separate management plans for recovery and conservation efforts.

A major disease damaging seedlings of Pinus palustris is caused by the fungus Mycosphaerella dearnessii. Population structure of this pathogen was studied in a population in Mississippi. High genetic diversity (0.65) was measured using microsatellite markers and coincides with the high number of vegetative compatibly groups observed. A 30 Mb genome sequence for a single isolate of M. dearnessii was assembled, representing 65% of the estimated genome size. Nearly all (93%) of the core set of genes present in eukaryotes were detected from a total of 10,996 predicted genes. A total of 853 enzymatic associations were identified along with several genes homologous to pathogenic genes in other fungal pathogens. These results provide insights into the infection process and host-pathogen interactions. Further investigating this pathosystem will lead to effective disease management strategies.

Arundinaria gigantea, a North American bamboo that historically grew in vast canebrakes, is now considered a critical component of an endangered ecosystem. Expressing self-incompatibility, restoration efforts must ensure genetic diversity within canebrakes for viable seed production. DNA fingerprinting methods were developed using 20 simple sequence repeat (SSR) markers and two sequence-characterized amplified region (SCAR) markers. Among 18 markers able to amplify rivercane DNA via polymerase chain reaction (PCR), 10 were demonstrated to be polymorphic within rivercane. Markers could distinguish rivercane among and between canebrakes and could discern full-sibling seedlings. The mostly-infertile Mississippi canebrakes of rivercane were determined to contain 46% genetic diversity within canebrakes and an average of 1.436 effective alleles. In contrast, the fertile North Carolina canebrakes contained 99% genetic diversity within canebrakes and an average of 6.435 effective alleles. Therefore, theoretically, at least seven distinct genotypes were needed for a healthy, viable rivercane brake.

Ceratocystis fimbriata is the type species for the genus Ceratocystis and was first described as the causal agent of black rot in sweet potatoes. However, evidence from DNA sequence data suggests that C. fimbriata is in fact a species complex (C. fimbriata sensu lato) consisting of many morphologically similar cryptic species. Species in this complex are pathogens of important root and fruit crops and trees in the forestry industry world-wide. Population studies on some of these species have mainly relied on microsatellite markers. However, nothing is known regarding the microsatellite structure within Ceratocystis species or any species in the order Microascales in which Ceratocystis resides. The need for a more robust identification tool is also required to differentiate between species in this complex. The first chapter of this thesis provides a review of the literature on microsatellite markers, particularly in fungi. It also discusses the history of microsatellites, mechanisms of microsatellite evolution and functional importance in selected fungal examples. In addition, isolation methodologies are compared and contrasted to newly developed techniques that include bioinformatic searches of genome sequences. Opportunities to use and develop microsatellite markers in Ceratocystis species is also discussed with an emphasis on the possibilities that more microsatellites markers would provide. Microsatellites are abundant in eukaryotic genomes, and fungi are no exception. Analyses of microsatellite content in eukaryotic and fungal genomes have shown that fungi contain fewer microsatellites and that each organism shows preference for particular motifs. In Chapter 2 of this thesis, the abundance and distribution of microsatellites in the recently sequenced C. fimbriata genome is investigated. Comparisons to other fungi and eukaryotes show that C. fimbriata follows the general pattern of microsatellite structure, however it is unique in its preference for certain motifs. The C. fimbriata sensu lato species complex contains morphologically indistinct species. Microsatellite markers previously developed for a population study could differentiate between some of the cryptic species based on their geographic location and host-specificity. In Chapter 3 a subset of microsatellite markers identified in gene regions in Chapter 2 are used to develop a diagnostic test to differentiate between species in the complex. Microsatellite markers that are polymorphic between species but monomorphic within species were selected for this purpose. However, not all species could be distinguished using this diagnostic test. This thesis is presented as a series of chapters in which Chapters 3 2 and 3 are in manuscript format. Consequently each chapter represents an independent article and repetition between these chapters has been unavoidable. / Dissertation (MSc)--University of Pretoria, 2014. / Genetics / Unrestricted

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Current studies of koalas in the wild mainly rely on information gathered by traditional field methods, such as community sightings, spotlighting, radiotracking, animal trappings, ear tagging and faecal pellet incidence. Collection of faeces is potentially the most reliable source of non-invasively obtaining DNA samples, which can be used to identify specific individuals. This thesis demonstrated a simple, rapid and reproducible method of extracting DNA from Koala faecal pellets using a commercially available DNA extraction kit, shows the maximum age of pellets from which DNA can be reliably extracted and defines the conditions required for the long term storage of pellets before DNA extraction is carried out. Mitochondrial DNA PCR analysis provided a simple and rapid indication of the success of both the faecal DNA extraction and pellet collection process. The faecal DNA was successfully used for microsatellite analysis and the subsequent genetic profiling of individuals from within the Campbelltown Koala population. The study paves the way for the analysis of microsatellite loci in koala faecal pellet DAN to study populations, which are too sparsely distributed to allow the capture of individual koalas / Master of Science (M. Sc.) (Hons.)

Dark (Microdipodops megacephalus) and pallid (Microdipodops pallidus) kangaroo mice are ecological specialists found in arid regions of the Great Basin Desert of the southwestern United States. Historical and current habitat alterations have resulted in disjunct distributions and severely diminished abundance of both species. Phylogenetic and phylogeographic research has discovered unique mitochondrial clades within M. megacephalus (eastern, central, western, and Idaho clades) and M. pallidus (eastern and western clades). Population-genetic analyses targeting the same mitochondrial markers also have found low amounts of maternal gene flow among the clades. However, little is known about population structure and genetic demography (historical and current migration rates, historical and current effective population sizes) within each mitochondrial clade. Herein, nuclear-encoded microsatellite loci were isolated to evaluate the underlying processes that may have molded kangaroo mouse relationships and distributions. Results from population-genetic analyses support previous findings that there are at least three genetically distinct clades within M. megacephalus and two such clades within M. pallidus. Three clades of M. megacephalus appear to have undergone different demographic histories, with little to no migration among clades. The two clades of M. pallidus also appear to have experienced varying demographic change although there has been small but recent migration between them. Additionally, the contemporary effective population sizes of all clades within Microdipodops appear to be low, suggesting that these populations may have difficulty coping with environmental pressures and hence are at risk of extinction. Results of this study are consistent with the recommendation that each Microdipodops clade should be managed as separate units and continually monitored in an effort to conserve these highly specialized taxa.