Genetic and evolutionary analysis of diversification and reproductive isolation in yeast

In this thesis, I examine the mechanisms of evolution at different levels, from evolutionary conflict between selfish genes within a single individual (Chapter 1), through social evolution acting within a species (Chapter 2), to genetic divergence and incompatibility between closely related species (Chapters 4 & 5). The thesis therefore investigates how tiny genetic differences occurring in individuals accumulate and produce discontinuous groups. The first chapter explores an interesting form of natural selection, acting independently on different genomes within the same cell. Natural selection can act at the level of individual genes: an allele that promotes its own transmission can increase in frequency despite reducing the fitness of the rest of the genome (Dawkins 1978). This phenomenon, known as intragenomic conflict (Hurst 1992), has long been hypothesized to drive evolution, forcing different lineages to adapt to the genes within their own genomes and therefore causing their genomes to diverge, and potentially, to become incompatible types. Here I test whether intragenomic conflict drives evolutionary change by evolving yeast populations in the laboratory, to see if intra-genomic conflicts would lead genomes in independent populations to become incompatible. After allowing populations to evolve under two treatments of strict vertical transmission of mitochondria, or mixed horizontal/vertical transmission, I tested the evolutionary changes in interactions between mitochondrial and nuclear genomes in the continuum of mutualism and selfishness. As predicted, increasing the independence of mitochondria from their hosts (by increasing outbreeding) reduced the evolved fitness benefit that mitochondria provided to their un-evolved hosts. The results presented in this chapter hint that intra-genomic conflicts can speed up the evolution of cyto-nuclear reproductive isolation between allopatric populations. The second chapter also looks at whether conflict, this time between individuals in a population rather ...