  Mechanisms leading to speciation are a major focus in evolutionary biology.
In this paper, we present and study a stochastic model of population where
individuals, with type a or A, are equivalent from ecological, demographical
and spatial points of view, and differ only by their mating preference: two
individuals with the same genotype have a higher probability to mate and
produce a viable offspring. The population is subdivided in several patches and
individuals may migrate between them. We show that mating preferences by
themselves, even if they are very small, are enough to entail reproductive
isolation between patches, and we provide the time needed for this isolation to
occur as a function of the population size. Our results rely on a fine study of
the stochastic process and of its deterministic limit in large population,
which is given by a system of coupled nonlinear differential equations.
Besides, we propose several generalisations of our model, and prove that our
findings are robust for those generalisations.
