On the mine tailings, it has evolved tolerance to heavy metals, which normally would kill this species There is a hybrid zone between but Mating between the two types is reduced because flowering times have partially diverged. Allopatric Geographic evidence is generally viewed as being consistent with allopatric. Keep two populations separate for many generations, often with different selection pressures Such experiments have almost never led to complete isolation. Drosophila paulistorum line started from a single gravid females collected from field in 1958. But for species pairs with overlapping ranges prezygotic isolation evovlves much more rapidly, consistent with reinforcement Importance of this finding not limited to reinforcement in allopatric speciation.
Ring species show that reproductive isolation can evolve without any genetic revolutions.
This is the observation that led Mayr to propose the peripheral isolate model in the first place. New Guinea kingfishers. Chromosomal differences between species. Some chromosomal differences appear difficult for selection to favor within populations because the heterozygotes are less fit. Example translocations of two chromosome fragments.