«Stability and variability of the genome and evolution »
Mme Myriam Gaujoux – Emilangues - 2011
In California, populations of these salamanders became separated geographically evolving over millions of years to adapt to different environments. They've changed so much that they're on their way to becoming entirely separate species.
David Wake of the University of California Berkeley explains the history of these species complex began about 10 million years ago on the edge of redwood forest in northern California.
What we have today, this form picta which is highly variable both genetically and in terms of coloration. There were two migratory routes followed by animals as they moved into southern California, one along the Sierra Nevada mountain chain where animals moved into the forest region, the other one along the coastal mountains. They avoided the great central valley. The populations that gradually moved down the forest region of California relied on blending in with their environment.
Animals with good camouflage tended to survive more and produce offspring with similar traits. As the salamanders progressed south over the millions of years the markings became more distinct. At the end of the chain in southern California, we have this form klauberi which is the extreme of variation showing the largest blotches, most ball marking. These were all camouflaged organisms that were hiding from predators. Along the coast a different strategy was followed. Here the organisms adopted the colour pattern and the behaviour of dangerously poisonous newts and they became instead of camouflaged, they were advertising their resemblance to these dangerously poisonous animals and gaining an advantage because of their mimicry.
So what happened is that you had two differently adapted lineages moving to the south and by the time they reached the southern end they had essentially evolved into different species. But at certain areas for example in
Palo mountain area in San Diego county we get these animals which are hybrids. And the hybrids are neither similar to the dangerously poisonous animals, they're not good mimics, nor are they good animals in terms of camouflage.
So these organisms are essentially dead ends. These hybrid offspring are not well adapted to their environment and are therefore less likely to survive. the two parent subspecies that produce the hybrids are well on their way to becoming entirely separate species evolving just as Darwin described in his theory of evolution.
I think Darwin would love this example because it shows exactly the sorts of patterns that he was talking about gradual adaptive divergence leading eventually to establish various species.