Séance Séminaire

Séminaire des Doctorant·e·s

When sinks become sources: adaptive colonization in asexuals.

The establishment success of a population into a new empty habitat outside of its initial niche is a phenomenon akin to evolutionary rescue in the presence of immigration (biological invasions by alien organisms, host shifts in pathogens or the emergence of resistance to pesticides or antibiotics from untreated areas). We derive an analytically tractable framework to describe the coupled evolutionary and demographic dynamics of asexual populations in a source-sink system. In particular, we analyze the influence of several factors - immigration rate, mutational parameters and harshness of the stress induced by the change of environment - on the success of the establishment in the sink (i.e. the formation of a self-sufficient population in the sink), and on the time until establishment. To this aim, we use a classic phenotype-fitness landscape (Fisher's geometrical model in n dimensions) where source and sink habitats determine distinct phenotypic optima. The dynamics of the full distribution of fitness and of population size in the sink are analytically predicted, under a strong mutation strong immigration limit, where the population is always polymorphic. The resulting eco-evolutionary dynamics depend on mutation and immigration rates in a non straightforward way. Below some mutation rate threshold, establishment always occurs in the sink, following a typical four-phases trajectory of the mean fitness. The waiting time to this establishment is independent of the immigration rate and decreases with the mutation rate. For a mutation rate greater than the threshold, lethal mutagenesis impedes establishment and the sink population remains so, albeit with an equilibrium state that depends on the details of the fitness landscape. We use these results to get some insight into possible effects of several management strategies.