Using tools as simple as rulers and as complex as DNA sequencers, Tom and his colleagues have learned a remarkable amount about Ensatina. We now have a fairly detailed picture of how the species moved throughout California and Oregon, backed up by evidence from morphology, proteins, and DNA. We know more about why the different subspecies have evolved the color patterns they did. And, with Tom’s most recent work, we are beginning to understand how all this squares with the most intriguing characteristic of a ring species: the distinct endpoints of the ring (eschscholtzii and klauberi), which don’t blend together even though the two groups are connected by continuous variation throughout the rest of the ring. Over the past 60 years of investigations, Robert Stebbins’ initial hypothesis about Ensatina‘s evolutionary history has grown into a much more detailed understanding of the animal. But there’s still much to learn.

Five years ago, Tom wondered if there was anything we didn’t know about Ensatina. Now he’s impressed by the magnitude of what we still don’t understand about these creatures. How long did it take them to diversify into the different subspecies? What other salamanders are they most closely related to? Have the differently colored subspecies evolved different strategies to avoid predators? What makes eschscholtzii females reject klauberi males? Why do they interbreed in some places but not others? All these questions, and many more, remain to be answered. Says Tom, “As you get new tools and new techniques, you’re always going to be able to ask new questions and learn new things. I don’t think that we’re ever going to get to a point where Ensatina is ‘done.'”

Discussion and extension questions:

1. In your own words, describe what a ring species is.
2. This article described the Ensatina ring species. Research another possible example of a ring species and explain why you think it might constitute a ring species.
3. What different lines of evidence support the idea that Ensatina is a ring species? List at least three and explain how each line of evidence supports the idea.
4. As Ensatina spread into new habitats it evolved. Explain how evolutionary changes in one of the following aspects of salamander biology might contribute to speciation: mating rituals, preferred habitat type, or reproductive physiology.
5. What question about Ensatina‘s evolution would you most like to have answered? What sort of evidence might help you answer that question?