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PhD defended in 2013
Direction: Didier Andrivon
 
Abstract:

Agricultural ecosystems under seasonality are characterized by periodic host plant absence, which may impact parasite evolution. Sustainable crop protection must incorporate parasite evolution. This requires a long-term epidemiological perspective, which is hardly amenable to experimentation, and makes multi-annual plant epidemic models particularly relevant. We consider a family of such models, termed semi-discrete models, which correspond to distinct life cycles, depending on the parasite reproduction mode (sexual or asexual) and its primary infection mode (airborne or soilborne, i.e. with or without negative density-dependence, respectively). Under the assumption of a trade-off between in-season multiplication and season-to-season survival, an adaptive dynamics approach shows that temporal niche differentiation can lead airborne parasites to diversify and coexist. These results assume a strictly asexual parasite life cycle, which does not correspond to all plant parasites. Some parasites produce survival forms by self-incompatible sexual reproduction. When sexual reproduction is mandatory, the need to find a mate induces positive density dependence at low density (demographic Allee effects). Under the assumption of a trade-off between in-season asexual multiplication and resource allocation to sexual survival forms, we show that evolution may lead to the coexistence of a strictly sexual morph with a cyclic parthenogenetic morph. Our findings provide a novel hypothesis (positive density dependance and Allee effects) for the frequent coexistence of sexual and asexual plant parasites.