Sympatric speciation driven by beneficial mutations

Published models of sympatric speciation through habitat specialization require balanced polymorphism at loci affecting fitness in different habitats, but the conditions for maintenance of such polymorphism are stringent. Here I suggest a complementary mechanism favouring the evolution of habitat races, regarded as a prelude to sympatric speciation. It rests on the assumption that beneficial mutations with habitat-specific effects frequently arise and become incorporated into gene pools. When a mutation with fitness effects differing between habitats spreads in the population, there is indirect selection favouring habitat choice over random dispersal. I studied this process in a two-locus, two-habitat computer simulation. The results suggest that the conditions favouring sympatric speciation are less stringent than previously thought.