Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [165]-180).

The inherent asymmetry of female meiosis presents an opportunity for genetic material to gain an evolutionary advantage during the formation of the egg. Since centromeres mediate chromosomal segregation by forming the bridge between microtubules and chromosomes during cell division, they are loci that can drive, or selfishly evolve, during female meiosis by manipulating the process of entering the egg. Mimulus guttatus, a species of yellow monkeyflowers, has the best documented case of centromeric drive (Fishman and Saunders, 2008). Since homozygotes for drive have decreased pollen viability, lower seed counts, and poor reproductive success, CENH3 —the gene that encodes the H3 histone specific to centromeres— has evolved to suppress centromeric drive. CENH3 is duplicated in Mimulus, and the sequence variation of CENH3_A suggests that this paralog can suppress centromeric drive during female meiosis (Finseth et al. 2015). Our analysis of gene expression levels in meiotic and mitotic tissues indicates that both CENH3_A and CENH3_B are still expressed at similar levels, suggesting that the paralogs have not specialized for different roles in cell divisions. However, qPCR was only performed with nine tissue samples, so further analysis of gene expression with a larger sample set is needed to confirm whether or not the CENH3 paralogs have specialized roles in meiosis and mitosis.

<p>In an ever-changing world, evolution is an essential process that may allow organisms to adapt to their environment through natural selection. All evolutionary processes act through a single fundamental medium: genetic variation. Polyploidy, or whole genome duplication, is a major mechanism for evolutionary change because it is both widespread across taxa and results in a proliferation of genetic material that evolution can act upon. The key questions addressed here are: (1) How does chromosome pairing during meiosis in allopolyploids affect the magnitude of genetic variation?, (2) How does the genome of polyploids evolve following formation, and what genetic mechanisms govern this evolution?, and (3) How does genetic and genomic evolution in polyploids affect phenotypic evolution? I use the shy monkeyflower, <italic>Mimulus sookensis</italic>, a tetraploid of hybrid origin between <italic>Mimulus guttatus</italic> and <italic>Mimulus nasutus</italic>, to address these focal questions. In order to develop a foundation to aid in interpretation of my findings, I first investigate the evolutionary history of <italic>M. sookensis</italic>. Chromosome counts establish that <italic>M. sookensis</italic> is indeed an allotetraploid, and a review of taxonomic literature reveals that this species is heretofore undescribed. By analysing the patterns of genetic variation at chloroplast and nuclear loci in <italic>M. guttatus</italic>, <italic>M. nasutus</italic>, and <italic>M. sookensis</italic>, I show that <italic>M. sookensis</italic> has recurrently formed from <italic>M. guttatus</italic> and <italic>M. nasutus</italic>. Crossing experiments within <italic>M. sookensis</italic> indicate that recurrent origins can contribute to genetic diversity without contributing to reproductive isolation among independently arisen polyploid lineages.</p><p>To address my focal questions, I take advantage of an intriguing and striking difference in flower size among <italic>M. sookensis</italic>, <italic>M. guttatus</italic>, and <italic>M. nasutus</italic>. The flowers of <italic>M. sookensis</italic> and <italic>M. nasutus</italic> are small and remarkably similar to one another, while the flowers of <italic>M. guttatus</italic> and diploid and tetraploid F1 hybrids between <italic>M. guttatus</italic> and <italic>M. nasutus</italic> are large and showy. This phenotypic divergence in flower size between <italic>M. sookensis</italic> and <italic>M. guttatus</italic>-like hybrids indicates that small flower size has evolved in <italic>M. sookensis</italic>. Using genetic marker data and phenotypic measurements from synthetic neoallotetraploid <italic>Mimulus</italic>, I demonstrate that there are low levels of fragment loss and phenotypic variation in neoallotetraploids; this suggests that homeologous pairing and recombination following polyploidization is not a major source of genetic variation or phenotypic evolution in <italic>M. sookensis</italic>. Analysis of the whole genome sequence of two <italic>M. sookensis</italic> lines reveals that <italic>M. sookensis</italic> is a fixed heterozygote throughout its entire genome, in that it has retained both a <italic>M. guttatus</italic>-like and <italic>M. nasutus</italic>-like subgenome, neither of which have been removed through homeologous recombination. These subgenomes have been homogenized by widespread gene conversion, and do not appear to have been differentially affected by deletions or deleterious mutations. Finally, to directly characterize the genetic architecture of flower size in <italic>M. sookensis</italic>, I cross a large-flowered synthetic neoallotetraploid <italic>Mimulus</italic> to small-flowered <italic>M. sookensis</italic>. I then employ a novel genotyping-by-sequencing approach to identify quantitative trait loci (QTL) associated with flower size. I find that there is one locus that accounts for a large proportion of phenotypic variation, and four other loci also contribute to flower size variation between the parental lines. Some of these loci co-localize with previously identified loci for flower size in diploid <italic>Mimulus</italic>, while others do not. Altogether, genetic marker data, phenotypic analysis of neoallotetraploids, whole genome sequence data, and QTL mapping data suggest that the genetic variation necessary for flower size evolution was likely caused by both gene conversion and new mutations, but not homeologous recombination. These results suggest that trait evolution in polyploids may be affected by the unique attributes of polyploids, but that new mutations are always an important source of genetic variation, regardless of ploidy level.</p> / Dissertation

No description available.

Pollinator-mediated competition and facilitation are two important mechanisms mediating co-flowering community assembly. Experimental studies, however, have mostly focused on evaluating outcomes for a single interacting partner at a single location. Studies that evaluate spatial variation in the bidirectional effects between co-flowering species are necessary if we aim to advance our understanding of the processes that mediate species coexistence in diverse co-flowering communities. Here, we examine geographic variation (i.e. at landscape level) in bidirectional pollinator-mediated effects between co-flowering and We evaluated effects on pollen transfer dynamics (conspecific and heterospecific pollen deposition) and plant reproductive success. We found evidence of asymmetrical effects (one species is disrupted and the other one is facilitated) but the effects were highly dependent on geographical location. Furthermore, effects on pollen transfer dynamics did not always translate to effects on overall plant reproductive success (i.e. pollen tube growth) highlighting the importance of evaluating effects at multiple stages of the pollination process. Overall, our results provide evidence of a spatial mosaic of pollinator-mediated interactions between co-flowering species and suggest that community assembly processes could result from competition and facilitation acting simultaneously. Our study highlights the importance of experimental studies that evaluate the prevalence of competitive and facilitative interactions in the field, and that expand across a wide geographical context, in order to more fully understand the mechanisms that shape plant communities in nature.

No description available.

<p>Evolution can be studied at many levels, from phenotypic to molecular, and from a variety of disciplines. An integrative approach can help provide a more complete understanding of the complexities of evolutionary change. This dissertation examines the ecology, genetics, and molecular mechanisms of the evolution of floral anthocyanin pigmentation in four species of <em>Mimulus</em> native to central Chile. Anthocyanins, which create red and purple colors in many plants, are a valuable model for studying evolutionary processes. They are ecologically important and highly variable both within and between species, and the underlying biosynthetic pathway is well characterized. The focus of this dissertation is dramatic diversification in anthocyanin coloration, in four taxa that are closely related to the genomic model system <em>M. guttatus</em>. I posed three primary questions: (1) Is floral diversification associated with pollinator divergence? (2) What is the genetic basis of the floral diversification? (3) What is the molecular mechanism of the increased production of anthocyanin pigment? The first question was addressed by evaluating patterns of pollinator visitation in natural populations of all four study taxa. The second question was explored using segregation analysis for a series of inter- and intraspecific crosses. One trait, increased petal anthocyanins in <em>M. cupreus</em>, was further dissected at the molecular level, using candidate gene testing and quantitative gene expression analysis. Pollinator studies showed little effect of flower color on pollinator behavior, implying that pollinator preference probably did not drive pigment evolution in this group. However, segregation analyses revealed that petal anthocyanin pigmentation has evolved three times independently in the study taxa, suggesting an adaptive origin. In addition to pollinator attraction, anthocyanins and their biochemical precursors protect against a variety of environmental stressors, and selection may have acted on these additional functions. Molecular analysis of petal anthocyanins in <em>M. cupreus</em> revealed that this single-locus trait maps to a transcription factor, <em>McAn1</em>, which is differentially expressed in high- versus low-pigmented flowers. Expression of the anthocyanin structural genes is tightly correlated with <em>McAn1</em> expression. The results suggest that <em>M. cupreus</em> pigmentation evolved by a mutation cis to <em>McAn1</em> that alters the intensity of anthocyanin biosynthesis.</p> / Dissertation

<p>While local adaptation has been frequently demonstrated via reciprocal transplant experiments, our understanding of the genetic basis of it remains minimal. There is a notable lack of studies that identify naturally segregating variants, determine the traits controlled by these variants and characterize their fitness effects in the field. Such studies are critical for understanding how spatially varying selective pressures can drive population divergence and maintain genetic variation. The experiments presented here aim to characterize the genetic basis of local adaptation to serpentine soils in Mimulus guttatus. First, I show that serpentine and non-serpentine populations of M. guttatus are locally adapted to soil habitat wherein non-serpentine plants are unable to survive on serpentine soils. Serpentine tolerance appears to come at a cost as serpentine plants are smaller in the juvenile stage than non-serpentine plants when grown at non-serpentine field sites. These size differences may limit the competitive ability of serpentine tolerant plants in non-serpentine habitats which tend to be more heavily vegetated than serpentine habitats. Next I identify environmental variables that are important selective agents in the serpentine habitat. Using hydroponic assays to isolate an individual chemical variable of serpentine soils - low calcium levels to high magnesium levels (low Ca:Mg ratio) - I show that serpentine and non-serpentine populations of M. guttatus have significant differences in tolerance to low Ca:Mg. I then characterize the genetic basis of these ecotypic differences in survival and tolerance using quantitative trait locus (QTL) mapping. I identify a single, major QTL that controls both the ability to survive on serpentine soils and tolerance to low Ca:Mg ratio which suggests that M. guttatus populations have adapted to serpentine soils through an ability to tolerate the low levels of Ca while simultaneously not suffering from Mg toxicity. Furthermore, I show that this same QTL controls ability to survive on serpentine soils in a second, geographically distant population. However, preliminary work suggests that the two populations are not equally tolerant to each other's soils indicating that either other loci also contribute to serpentine tolerance and these are not shared between the two serpentine populations or that there are different serpentine tolerance alleles at the major QTL are not functionally equivalent. This work addresses long-standing questions in evolutionary biology regarding the number and effect size of loci that underlie adaptive traits by identifying a large effect locus that contributes to adaptive differences between M. guttatus populations.</p> / Dissertation

Premise of The Study: Studies on the effects of heterospecific pollen (HP) transfer have been focused mainly on insect-pollinated species, despite evidence of insect visitation to wind-pollinated species and transfer of their pollen onto stigmas of insect-pollinated plants. Thus, the potential consequences of HP transfer from wind-pollinated species remain largely unknown. Furthermore, accumulation of pesticide residues in pollen of wind-pollinated crops has been documented, but its potential effects on wild plant species via HP transfer have not been tested. Methods: We evaluated the effect of wind-dispersed Zea mays pollen on pollen tube growth of the insect-pollinated Mimulus nudatus via hand pollinations. We further evaluated whether pesticide-contaminated Z. mays pollen has larger effects on M. nudatus pollen success than non-contaminated Z. mays pollen. Key Results: We found a significant negative effect of Z. mays pollen on M. nudatus pollen tube growth even when deposited in small amounts. However, we did not observe any difference in the magnitude of this effect between pesticide-laden Z. mays pollen and non-contaminated Z. mays pollen. Conclusions: Our results suggest that wind-pollinated species can have negative effects as HP donors on insect-pollinated recipients. Thus, their role in shaping co-flowering interactions for wind- and insect-pollinated species deserves more attention. Although we did not find evidence that pesticide contamination increased HP effects, we cannot fully rule out the existence of such an effect, because pollen load and thus the pesticide dose applied to stigmas was low. This result should be confirmed using other HP donors and across a range of HP loads, pesticide types, and concentrations.

<p>The problem is two fold: how does natural selection operate on systems of interacting genes and how does natural selection operate in natural populations. To address the first problem, I have conducted a theoretical investigation into the evolution of control and the distribution of mutations in a simple system of interacting genes, a linear metabolic pathway. I found that control is distributed unevenly between enzymes, with upstream enzymes possessing the greatest control and accumulating the most beneficial mutations during adaptive evolution. To address the second problem, I investigated the evolution of copper tolerance in the common yellow monkeyflower, Mimulus guttatus. I genetically mapped a major locus controlling copper tolerance, Tol1. A Dobzhansky-Muller incompatibility was hypothesized to also be controlled by Tol1, however, we have demonstrated that it maps to another, tightly linked locus, Nec1. Finally, we investigated the parallel evolution of copper tolerance in multiple new discovered mine populations. We found that copper tolerance has evolved in parallel multiple times via at least two distinct physiological mechanisms. In four mine populations, there was a strong signal of selection at markers linked to Tol1, implying that copper tolerance has evolved via the same genetic mechanisms in these populations.</p> / Dissertation