Résumé
Polymorphic dispersal strategies are found in many plant and animal
species. An important question is how the genetic variation underlying
such polymorphisms is maintained. Numerous mechanisms have been discussed,
including kin competition or frequency-dependent selection. In the context
of sympatric speciation events genetic and phenotypic variation is often
assumed to be preserved by assortative mating. Thus, recently, this has
been advocated as a possible mechanism leading to the evolution of
dispersal polymorphisms. Here, we examine the role of assortative mating
for the evolution of trade-off driven dispersal polymorphisms by modelling
univoltine insect species in a metapopulation. We show that assortative
mating does not favour the evolution of polymorphisms. On the contrary,
assortative mating favours the evolution of an intermediate dispersal type
and a uni-modal distribution of traits within populations. As an
alternative mechanism dominance may explain the occurrence of two discrete
morphs.