Auswirkungen von räumlichem Populationswachstum auf die genetische Vielfalt

Abstract

The growth of a population accompanied by a subsequent distribution into new territories is referred to as a range expansion. In the course of evolutionary history, many species extended their range, amongst others due to climate change and spreading of individuals. During range expansions, spatially structured distributions of neutral genetic variants may emerge as a consequence of an effect called gene surfing. However, such distributions may also resemble those distributions caused by processes of natural selection. In order to correctly interpret observed genetic data, it is inevitable to quantitatively understand the influence of range expansions on genetic diversity. In this thesis I characterize the consequences of range expansions for allele frequency spectra. To this end, I utilize computer simulations to generate genetic data to study various demographic scenarios subject to different ecological and geographic conditions. I show that range expansions can rapidly lead to allele frequency spectra obeying power laws with a characteristic exponent. The value of this exponent lies within the range of exponents expected for stable and exponentially growing well-mixed populations. According to my results, mutations that occurred during a range expansion contribute less to today's allele frequency spectra when compared to mutations that were already present in the original population. However, recent mutations are better suited to detect range expansion in genetic data, as their distribution is less influenced by geographical structures. My results will help to detect traces of past range expansions in genetic data to uncover the evolutionary history of species.