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Population and adaptive dynamics of feminizing symbionts

2010Population and adaptive dynamics of feminizing symbiontLIU Ning (China)
Organisation:University of Poitiers, Poitiers (FR) - Université Paul Sabatier, Toulouse (FR)Supervisor :Mathieu Sicard (UP) & Jean-Baptiste Ferdy (UPS)
Summary: Though commonly believed to influence remarkably on the ecological and evolutionary dynamics of host population, the consequence of feminizing symbionts has only been poorly investigated by mathematical models. In this thesis, we modelised the dynamics of a feminizing symbiont transmitted perfectly through maternal lineage. The population dynamics approach shows that the ecological impact of feminizing symbiont varies depending on the strength of male limitation onto female fecundity. Interestingly, the feminizers can change the threshold of extinction for small host populations through Allee effects, or act mutualistically by increasing host's fecundity. The adaptive analysis shows that male limitation alone can not counteract selection towards higher feminization. Thus, maximum feminization ratio will be selected and lead to evolutionary suicide of host population. If higher virulence (i.e. extra mortality) accompanies stronger feminization, the feminization ratio may be stablized at an intermediate Evolutionarily Stable Strategy (ESS). However the level of ESS feminization ratio is also under influence of natural mortality rate. This reflects that reproduction benefit due to feminization is limited by population density at the equilibrium. Our study also emphasizes that Horizontal transmission (HT) is necessary in some ecological situations for the symbiont to start invasion and even prevail in the host population.