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Dernière mise à jour : Mai 2018

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Reichel Katja

Effects of partial asexuality on the dynamics of genotype fraquencies in dominantly diploid populationsInference and modeling of the impacts of partially asexual reproduction on the genomic diversity of populations

Thesis started novembre1st, 2011, defended in december 10th 2015
Fund : ARED / INRA
Direction : Solenn Stoeckel & Jean-Christophe Simon

Abstract:

Reproductive systems determine how genetic material is passed from one generation to the next, making them an important factor for evolution. Organisms that combine sexual and asexual/clonal reproduction are very widespread, both throughout the earth’s biomes and on the eukaryotic tree of life. However, the effects of their reproductive system on their evolution are still controversial and poorly understood. The aim of this thesis was to model the dynamics of genotype frequencies under combined sexual/clonal reproduction in dominantly diploid life cycles, with the view of establishing a reference for future field studies. This involves two subtypes of partially clonal reproduction: either both reproductive modes co-occur (“acyclic partial clonality”), or they alternate (“cyclic clonality”). For both, a state and time discrete Markov chain model served as the mathematical basis to describe changes of the genotype frequencies through time.

The results demonstrate that partial clonality may indeed change the dynamics of genomic diversity compared to either exclusively sexual or exclusively clonal populations. Moreover, both subtypes have different effects under selectively neutral conditions: while acyclic partial clonality leads to increased variation in the frequency of heterozygous genotypes within the population, the patterns observed under cyclic clonality depend on the sampling time (before or after sexual reproduction) and show a stronger effect on allele frequencies. The dynamics of population heterozygosity were also slowed down under acyclic partial clonality, yet this effect did not generally lead to slower adaptation under selection. Time has a crucial role in partially clonal populations and needs to be taken into account in any analysis of their genomic diversity. This thesis provides recommendations for data collection and a null hypothesis for the interpretation of population genetic/genomic data from dominantly diploid partially clonal organisms. Moreover, it includes new methods for the analysis of genotype-based population genetic Markov chain models. These results have a high potential relevance in several areas, ranging from basic research, e.g. on the evolution of sex and speciation, to applications in agriculture (e.g. partially clonal crops, pests and pathogens), fisheries (e.g. primary producers and plankton) and nature conservation (e.g. threatened or invasive species).