"Emergence of multiple mergers from population structure: the case of semi-pushed fronts"Foutel-Rodier, FélixConsider a population where individuals are structured according to some types (spatial locations, genotypes) that influence their reproductive success. If types are heritable, an individual that reaches a region of high fitness will produce a highly successful offspring and can have a large number of descendants in a few generations, through a snowball effect. At the level of the genealogy, this event can lead to the emergence of multiple mergers, departing from the standard prediction of population genetics that genealogies follow Kingman's coalescent. In this presentation, I will suppose that the dynamics of the population is described by a branching process and give an analytical criterion under which we believe that the genealogy of the population displays multiple mergers. Intuitively, this criterion expresses that the distribution of fitnesses over types (quantified by Fisher's reproductive value) is highly skewed. I will illustrate this general phenomenon on the specific example of one-dimensional range expansions. More precisely, I will show that the genealogy of a model of semi-pushed fronts proposed by Tourniaire (2021) converges to that of an alpha-stable continuous state branching process, verifying a conjecture of Birzu et al. (2021) in this context. This is joint work with Julie Tourniaire and Emmanuel Schertzer. |
« back