Two subspecies of salamanders in Southeast Asia, salamander S1
and Salamander S2, are thought to have diverged genetically and
morphologically through run speciation. At the souther tip of their
respective native ranges, they can co-occur in secondary contact.
They can mate successfully and produce viable, fertile offspring;
the offspring can therefore also reproduce. However, the hybrid
offspring have a coloration that is disproportionately attractive
and easily detectable by predators, leading to decreased
survival.
The relatively low fitness of the S1...