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Role of genetic variance in speciation
Payne, Pavel ; Markoš, Anton (advisor) ; Rueffler, Claus (referee)
Sympatric speciation has received much attention both empirically and theoretically. However, the contribution of sympatric speciation to biodiversity remains unclear. One piece missing from the speciation puzzle is the plausibility of sympatric ecological divergence of species through adaptation in polygenic traits. I consider an environment consisting of two niches, where one value of the trait is advantageous in only one niche, and vice versa. The selection regime is described by a trade-off in viabilities between the niches. These polygenic traits can, and often do, involve epistatic interactions among and between loci, so that the contribution of the alleles to viability deviates from additivity. Epistasis then also affects the curvature of the trade-offs: predominant less-than-additive epistasis turns the curve towards concavity and predominant more-than-additive towards convexity. The curvature of the trade-off plays a crucial role in the evolution of populations. With a convex trade- off, extreme values of the trait are favored and the population tends to diverge, but relatively stringent symmetry in strength of selection within the niches and the niche proportions is necessary to maintain polymorphism. In this study I use two and three- locus haploid versions of Levene's model to...
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The strength and mechanisms of postzygotic breeding barriers between diploids and polyploids in plants
Petříková, Eliška ; Čertner, Martin (advisor) ; Bohutínská, Magdalena (referee)
The aim of this literature survey is to focus on whole genome duplication as a mechanism of sympatric speciation in plant populations, to explain the principals of reproductive isolation between neopolyploids and their diploid ancestors and to discuss the efficiency of reproductive isolation among various plant species. The mechanism of so-called triploid block will be introduced in this thesis. Triploids block is a form of postzygotic reproductive isolation which is realized during interpolidy crosses. The two main mechanisms of triploid block are the hybrid inviability, means production of inviable hybrid seed, and reduced fertility of triploid hybrids by production of aneuploid or inviable gametes. The efficiency of triploid block varies between plant species and these differences will be also discussed. The reduction in reproductive isolation often leads to gene flow between cytotypes. Mechanisms and intensity of gene flow between cytotypes of various species will be also introduced. In the end, this thesis will be enriched with a summary of existing knowledge about cytotype variability in populations of Butomus umbellatus, the model species for following master's thesis.
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Role of genetic variance in speciation
Payne, Pavel ; Markoš, Anton (advisor) ; Rueffler, Claus (referee)
Sympatric speciation has received much attention both empirically and theoretically. However, the contribution of sympatric speciation to biodiversity remains unclear. One piece missing from the speciation puzzle is the plausibility of sympatric ecological divergence of species through adaptation in polygenic traits. I consider an environment consisting of two niches, where one value of the trait is advantageous in only one niche, and vice versa. The selection regime is described by a trade-off in viabilities between the niches. These polygenic traits can, and often do, involve epistatic interactions among and between loci, so that the contribution of the alleles to viability deviates from additivity. Epistasis then also affects the curvature of the trade-offs: predominant less-than-additive epistasis turns the curve towards concavity and predominant more-than-additive towards convexity. The curvature of the trade-off plays a crucial role in the evolution of populations. With a convex trade- off, extreme values of the trait are favored and the population tends to diverge, but relatively stringent symmetry in strength of selection within the niches and the niche proportions is necessary to maintain polymorphism. In this study I use two and three- locus haploid versions of Levene's model to...
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