For my PhD, I continued to work on a similar topic as in my master thesis, studying eco-evolutionary dynamics of species during range expansion and invasions. Where I started out in my master thesis with the already small spider mite Tetranychus urticae, I now moved on to the even smaller world of protists, using the ciliate Tetrahymena thermophila as a model species. Reading up on the literature, I became interested in the gene swamping theory, which predicts that sex can hinder adaptation during range expansions, in populations spreading into an abiotic gradient, if long distance gene flow floods the population at the range edge with maladapted individuals. Although this framework is extensively studied from a theoretical point, few empirical or experimental attempts have been made to validate this theory. I got interested in trying to test the gene swamping theory experimentally, and hence, the ultimate goal of my PhD is to assess how how abiotic gradients in the environment alter range expansion dynamics and evolution in populations reproducing either asexually or sexually, and in absence or presence of long distance gene flow from the core region to the range edge of a species. I aim to do this not only through experimental evolution using the aforementioned protists, but also through whole genome sequencing of experimental evolution lines to assess the genomic basis and consequences of range expansions, as well as using a theoretical approach using individual based modelling, to investigate aspects of range expansions that are unfeasible to test through experimental evolution. By combining these microcosm experiments, genomic analyses and models, I aim to gain further understanding of both the genomic basis of evolutionary adaptations in expanding populations, as well as how sex, gene flow and abiotic change in the environment alter evolutionary dynamics of populations.