Does adaptation to different diets result in assortative mating? Ambiguous results from experiments on Drosophila.

The emergence of behavioural isolation between populations under divergent selection can be crucial for ecological speciation, but the mechanisms underlying such isolation are poorly understood. Several experimental evolution studies have shown that positive assortative mating (preference for similar mates) can arise rapidly in Drosophila laboratory populations reared in different stressful conditions, while other studies failed to confirm this effect. Here, we present the results of an evolution experiment in which outbred lines of Drosophila melanogaster were reared for 1-2 years on one of the three different diets (standard, starch based or high salt).