Cranberry (Vaccinium macrocarpon), a commercially grown evergreen dwarf shrub, is a dominant taxon in temperate bogs in North America. It spreads clonally by runners, and reproduces sexually predominantly by self-fertilization on upright stems. The objective of this project was to investigate genetic and clonal variation and phenotypic plasticity of V. macrocarpon. Specifically, I wanted to test whether there exists an inverse relationship between population genetic variation and the amount of overall phenotypic plasticity of vegetative characteristics. As background information I assessed the vegetation and edaphic factors of marginal cranberry bogs found in the mid-to-southern Appalachians. A gradient of nutrient availabilities was found among bogs that was positively associated strongly with the dominance of the more generalist Rubus hispidus and negatively with ericaeous bog shrubs such as V. macrocarpon. Eutrophication may lead to the replacement of endemic bog species with generalist plastic species. Theoretically, it would be plausible for environmental heterogeneity or stress to allow selection for more phenotypically plastic clones within a species. A single adaptively plastic clone for growth strategy could sweep a site, excluding intraspecific competitors. That is, selection could favor clones with high plasticity that could subsequently lead to a loss of genetic variation within a population. The environmental and genetic conditions favoring this would more likely exist in distributionally marginal sites because of spatial and temporal heterogeneity and island-like biogeography. Field and common garden experiments in which nutrients were manipulated were performed to test for an inverse relationship between phenotypic plasticity and genetic heterogeneity. Random amplified polymorphic DNA (RAPD) profiling was coupled with ecological measurements of plant growth on the experimental clones and other clones from the experimental populations to estimate genetic heterogeneity. Genetic heterogeneity was found to be significantly lower in marginal populations than in central populations. Phenotypic plasticity was somewhat higher in a more marginal population in the field sites, but direct statistical comparisons could not be made. The common garden study was inconclusive, possibly due to transplant shock, but a trend among natural populations was towards higher plasticity among marginal clones. Additional research on other species is needed to clarify the possible inverse relationship between phenotypic plasticity and genetic variation within populations. / Ph. D.

Genetic variation was examined at 19 loci encoding enzymatic and general proteins Notropis lutrensis from the Brazos River in Texas. The thermal regime of the Brazos River below Possum Kingdom Reservoir is altered due to the release of water from the hypolimnion. Summer water temperatures fluctuate as much as 7^oC. Levels of heterozygosity at the malate dehydrogenase-2 locus were correlated with the degree of water temperature fluctuation at each locality. The isozymes from three homozygous patterns of supernatant malate dehydrogenase (Mdh-l, Mdh-2) exhibited different activities at different experimental temperatures.

[Truncated abstract] The species-rich Southwest Australian Floristic Region (SAFR) is a global biodiversity hotspot. Characterised by a Mediterranean-type climate and nutrient deficient landscape, this region is endowed with 7380 native vascular plant species/sub species, of which 49% are endemic and 2500 are of conservation concern. Despite the global significance of this region, there is still only a poor understanding of the factors influencing high diversity and endemism, and especially the population genetic consequences of narrow endemism and naturally fragmented species distribution. Holly leaved banksia (Banksia ilicifolia R. Br.), although widespread through Southwest Western Australia (SWWA), has a naturally fragmented distribution, with generally small populations restricted to swales and wetland fringes with depth to groundwater less than 10 m. As such, it provides an excellent model to better understand the ecological genetic consequences of local endemism, population size and natural population fragmentation . . . Products of wide outcrossing (over 30 km) showed a heterosis effect over local outcrossing, indicating increased ecological amplitude of offspring following interpopulation mating. These results suggest that the breeding and mating biology of B. ilicifolia counters the negative genetic erosion effects of narrow ecological amplitude and small population size. Recent habitat fragmentation, and reductions in population size and increased isolation, is impacting on these processes, but further research is required to assess the ultimate consequences of these genetic effects for population viability.

<p>The systematic and population genetic relationships were characterised for three ecologically related euphausiid species: Euphausia lucens, E. recurva and E. vallentini. These species have different geographical distributions and life histories. All three species have a circumpolar distribution in the Southern Hemisphere while E. recurva is also distributed in the North Pacific. DNA sequence variation was determined for three regions of mitochondrial DNA and a single nuclear gene. It was conclusively demonstrated that both E. lucens and E. vallentini represent valid taxonomic species with fixed differences observed in both the nuclear and mitochondrial genes and that the low divergences previously reported for these species with 16SrRNA and CO1 resulted from a species misidentification. It was also shown that previous attempts to date the divergence between Antarctic and Sub-Antarctic euphausiid species based on 16SrRNA distances suffer from a large overestimation due to a calculation error.</p>

Selection in spatially heterogeneous environments is a convenient explanation for the high levels of genetic variation observed in natural populations. Indeed, theoretical studies predict that spatial heterogeneity leads to higher levels of variation in a variety of selection models. These models, however, have assumed quite restrictive parameters (e.g., two alleles, fixed gene flow and specific selection schemes). Therefore, the effect on spatial heterogeneity is still poorly understood for a wider range of parameters (e.g., multiple alleles, different levels of gene flow and more general selection schemes). We have relaxed some of the assumptions that have limited the previous models and studied the effect of spatial heterogeneity using simple single-locus viability selection models. First, we investigate the rarity of the parts of fitness space maintaining variation for multiple alleles and different levels of gene flow by randomly sampling that space using a "fitness space" approach. The volume of fitness space maintaining variation is always larger in a spatial model compared to a single-population model regardless of gene flow. Moreover, this volume is relatively larger for higher numbers of alleles, indicating that spatial heterogeneity is more efficient maintaining higher levels of variation. Second, we investigate the ease with which a more natural process of recurrent mutation and selection evolves to the particular area of fitness space maintaining variation using a "construction" approach. Depending on the amount of gene flow, the construction approach leads to both higher and lower levels of variation compared to a single-population model. Thus, spatial heterogeneity can both constrain and promote the ease with which a natural process of mutation and selection evolves to maintain variation. Also, the construction approach results in variation being maintained in a more stable subset of the volume of fitness space than the volume that resulted from the fitness space approach. Third, we investigate the effect of higher and lower levels of spatial environmental heterogeneity using the construction approach. The different levels of heterogeneity and gene flow interact to influence the amount of variation that is eventually maintained and this interaction effect is especially strong for intermediate levels of gene flow. More heterogeneous environments can maintain higher levels of variation, but selection in these environments also results in a higher level of migration load, lowering the final amount of adaptation that is achieved by the simulated evolutionary process. Finally, we investigate effect of genetic drift and finite populations using the construction approach. Interestingly, two different effects emerge for smaller and larger populations; in smaller populations genetic drift lowers the amount of variation as expected, whereas, more surprisingly, genetic drift increases the amount of variation in larger populations. Overall, spatial heterogeneity has profound effects on the outcome of selection, resulting in elevated levels of genetic variation for a wide variety of parameters.

Not available / text

Wind-pollinated plants often have little genetic structure owing to high gene flow. However, sex chromosomes evolution promotes divergence, potentially leading to population subdivision. Rumex hastatulus (Polygonaceae) is a wind-pollinated, dioecious coloniser of open disturbed land with two sex chromosome races (SCRs), which occupy different parts of the species’ range in the southern USA. My thesis investigated phenotypic and genetic differentiation between the SCRs, based on a study of 28 populations sampled throughout the range. A glasshouse experiment demonstrated significant differentiation between the SCRs in several life-history traits, several of which exhibited clinal variation. Analysis of population genetic structure, based on 13 nuclear loci, revealed two distinct clusters corresponding to the two SCRs, with an estimated origin of the North Carolina SCR from the Texas SCR between ~5000–15000 generations ago. My results indicate that the SCRs have developed a moderate degree of phenotypic and genetic differentiation despite ongoing gene flow.

<p>The systematic and population genetic relationships were characterised for three ecologically related euphausiid species: Euphausia lucens, E. recurva and E. vallentini. These species have different geographical distributions and life histories. All three species have a circumpolar distribution in the Southern Hemisphere while E. recurva is also distributed in the North Pacific. DNA sequence variation was determined for three regions of mitochondrial DNA and a single nuclear gene. It was conclusively demonstrated that both E. lucens and E. vallentini represent valid taxonomic species with fixed differences observed in both the nuclear and mitochondrial genes and that the low divergences previously reported for these species with 16SrRNA and CO1 resulted from a species misidentification. It was also shown that previous attempts to date the divergence between Antarctic and Sub-Antarctic euphausiid species based on 16SrRNA distances suffer from a large overestimation due to a calculation error.</p>

A fragment of the Claviceps purpurea pyr4 gene, encoding the enzyme orotidine-5'-monophosphate decarboxylase (OMPdecarboxylase) was used to screen a genomic library to an isolate (designated Lp1) of an Acremonium sp. which grows as an endophyte in perennial ryegrass (Lolium perenne). Four positive clones, λMC11, λMC12, λMC14 and λMC20 were isolated. Three of these clones, λMC12, λMC14 and λMC20 were overlapping clones from the same locus, while λMC11 was from a different locus. Fragments of these clones which hybridised with C. purpurea pyr4 were sequenced and found to have similarity with pyr4 from other fungi of the Pyrenomycetes and related Deuteromycetes, suggesting that Lp1 has evolved from a sexual Pyrenomycetes species. The pyr4 from λMC12, λMC14 and λMC20 was designated pyr4-1 and that from λMC11 was designated pyr4-2. The predicted ORFs of the two genes were highly conserved and the 5' non-coding nucleotide sequences were the least conserved regions. RT-PCR and northern analysis of total RNA from Lp1 demonstrated that transcripts approximately 1.4 kb in length were produced from the two genes and present at similar levels. Genomic fragments containing pyr4-1 or pyr4-2 were transformed into a strain of Aspergillus nidulans which has a mutation in the pyrG gene (encoding OMPdecarboxylase). Both of the Lp1 pyr4 complemented a pyrG mutation in Aspergillus nidulans, confirming that both pyr4-1 and pyr4-2 encode functional OMPdecarboxylases. Comparisons of pyr4 restriction fragment length polymorphisms (RFLPs) from Lp1 and isolates of Epichloë typhina, E. festucae, A. lolii, A. uncinatum, and three endophyte taxonomic groupings from Festuca arundinacea: FaTG-1 (=A. coenophialum), FaTG-2 and FaTG-3 suggested that pyr4-1 originated from E. typhina, the ryegrass choke pathogen, and pyr4-2 originated from A. lolii, another endophyte from perennial ryegrass. This suggested that Lp1 is an interspecific hybrid, between E. typhina and A. lolii. Comparisons of the variable 5' non-coding nucleotide sequences from pyr4 of Lp1 and other isolates demonstrated that E. typhina, and A. lolii or E. festucae were the most likely ancestors of the two pyr4 found in Lp1. The A. lolii and E. festucae sequences were very similar, suggesting they are closely related. A. lolii has most probably evolved from an E. festucae, and in the process lost the sexual cycle. Analysis of single spore purified isolates of Lp1 revealed that Lp1 was a homokaryon for pyr4. A Southern blot of a CHEF gel of Lp1 and these single spored isolates was hybridised to a pyr4 probe and demonstrated that pyr4-1 and pyr4-2 were present on either two chromosomes of similar size, or one chromosome. The hybridisation that gave rise to Lp1 was concluded to have been a relatively recent event, given the similarity of pyr4-1 and pyr4-2 nucleotide sequences to those of their probable ancestors, and the fact that both genes are expressed and functional. Interspecific hybridisation is probably widespread in the asexual endophytes, and may be an important event in their evolution, and the evolution of other fungal species.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.