FOR 1078: Natural Selection in Structered Populations
Medicine
Final Report Abstract
The goals of the Research Unit were to detect natural selection in populations with complex demography and structure, with a focus on wild tomatoes, mice and Drosophila and an emphasis on detecting signatures of selection at the genome level. Furthermore, the role of population structure on resistance and virulence in ants and the role of hybridization in the colonization of new habitats in Daphnia were investigated. All empirical studies were pursued in close interaction with the theoreticians of the Research Unit. The highlights of this six-year process can be summarized as follows. Development of the theory of selective sweeps: Selective sweeps caused by beneficial alleles going to fixation were used predominantly to find evidence of positive selection in the genome. The theory of selective sweeps was greatly extended in this six-year period such that it is now widely applicable to structured populations and complex demographies. Furthermore, competing sweeps have been analyzed and the question of the occurrence of selective sweeps at quantitative trait loci has been investigated. Finally, a flexible simulation tool has been developed to analyze natural selection in structured populations. Empirical studies of population structure and natural selection in Drosophila, mice and wild tomatoes: Evidence for positive directional selection leading to selective sweeps was found in several Drosophila studies. This work was accompanied by thorough analyses of gene expression differences between tropical and temperate Drosophila populations, which showed ample evidence of selection. Furthermore, canalization of gene expression was identified as a major signature of regulatory cold adaptation in temperate populations. A strong case of balancing selection was detected in mice. Thorough analyses of population structure were performed in wild tomatoes based on a newly developed fast composite likelihood approach (Jaatha) to estimate demographic parameters. This program will eventually be extended to detect selection. The role of population structure on resistance and virulence and the role of hybridization in the colonization of new habitats: These two ecological projects used genetic data to analyze the population structure of ants and Daphnia, respectively. In the case of ants, it could be shown that a metapopulation structure facilitates the evolution of altruistic defense traits. In the other case, hybridization appears to be the key for successfully colonizing new habitats. In both cases, modeling based on combined field and lab data was used to support the conclusions. In all cases the interaction between the different projects was very close, in particular that between theoreticians and empiricists, as can be seen in the joint publications.
