Drosophila pseudoobscura
In 1989 Diane Dodd gave laboratory populations of D. pseudoobscura two different food types, starch and maltose. They rapidly evolved into two distinct groups after only eight generations with the different foods. As the two groups both showed a strong preference for mating with their own type, this was claimed as an example of speciation by reproductive isolation. Dodd's experiment has been repeated by others, and works with other kinds of fruit flies and foods.