to have played a role in contributing to the differentiation of some taxa and to have sharpened boundaries in the Sierra Nevada (17). Instead, in California there has been a history of extensive geomorphological evolution coinciding with the history of the Ensatina complex. The time and space dimensions of the diversification are interconnected. The history of this complex has probably featured substantial isolation, differen
tiation, and multiple recent acts (Fig. 7). In effect, there are rings within rings in this complex, resulting from many levels of history being manifest in a single complicated pattern of variation, expressed somewhat differently at the three levels investigated to date—DNA sequences, allozymes, and color pattern. While the complex appears to be in a state of incipient species formation, which makes taxonomy problematic, it provides an instructive evolutionary example.
I thank M.Frelow, T.Jackman, D.Nguyen, C.Schneider, and K.P. Yanev for their extensive laboratory assistance, and C. Brown and many other individuals who have helped me in field work. Illustrations are by K.Klitz. I have benefited from discussions, comments on the manuscript, or both, with R.Bello, C.Brown, M.Garcia Paris, C. Haddad, R.Highton, T.Jackman, S.Kuchta, M.Mahoney, D.Parks, C.Schneider, R.Stebbins, M.Wake, K.Yanev, and K.Zamudio. The manuscript was improved by comments from two anonymous reviewers. This work was supported by grants from the National Science Foundation and the Gompertz Professorship.
1. Dobzhansky, T. (1937) Genetics and the Origin of Species (Columbia Univ. Press, New York).
2. Mayr, E. (1942) Systematics and the Origin of Species (Columbia Univ. Press, New York).
3. Ghiselin, M. (1974) Syst. Zool. 23, 536–544.
4. Avise, J.C. & Wollenberg, K. (1997) Proc. Natl. Acad. Sci. USA 94, 7748–7755.
5. deQueiroz, K. (1997) in Endless Forms: Species and Speciation, eds. Berlocher, S. & Howard, D. (Oxford Univ. Press, Oxford), in press.
6. Dobzhansky, T. (1958) in A Century of Darwin, ed. Barnett, S.A. (Harvard Univ. Press, Cambridge, MA), pp. 19–55.
7. Stebbins, R.C. (1949) Univ. Calif. Publ. Zool. 48, 377–526.
8. Stebbins, R.C. (1957) Evolution 11, 265–270.
9. Brown, C.W. & Stebbins, R.C. (1965) Evolution 18, 706–707.
10. Brown, C.W. (1974) Univ. Calif. Publ. Zool. 98, 1–64.
11. Larson, A., Wake, D.B. & Yanev, K.P. (1984) Genetics 106, 293–308.
12. Wake, D.B. & Yanev, K.P. (1986) Evolution 40, 702–715.
13. Wake, D.B., Yanev, K.P. & Brown, C.W. (1986) Evolution 40, 866–868.
14. Wake, D.B., Yanev, K.P. & Frelow, M.M. (1989) in Speciation and its Consequences, eds. Otte, D. & Endler, J.A. (Sinauer, Sunderland, MA), pp. 134–157.
15. Moritz, C., Schneider, C.J. & Wake, D.B. (1992) Syst. Biol. 41, 273–291.
16. Frost, D. & Hillis, D. (1990) Herpetologica 46, 87–104.
17. Jackman, T. & Wake, D.B. (1994) Evolution 48, 876–897.
18. Highton, R. (1997) Herpetologica, in press.
19. Tilley, S.C. & Mahoney, M.J. (1996) Herpetol. Monogr. 10, 1–42.
20. Dobzhansky, T. (1951) Genetics and the Origin of Species (Columbia Univ. Press, New York), 3rd Ed.
21. Nei, M. (1972) Am. Nat. 106, 283–292.
22. Highton, R. (1995) Annu. Rev. Ecol. Syst. 26, 579–600.
23. Stebbins, R.C. (1954) Univ. Calif. Publ. Zool. 54, 47–124.
24. Staub, N.L., Brown, C.W. & Wake, D.B. (1995) J. Herpetol. 29, 593–599.
25. Avise, J. (1994) Molecular Markers, Natural History and Evolution (Chapman & Hall New York).
26. Graybeal, A. (1995) Syst. Biol. 44, 237–250.
27. Yanev, K.P. (1980) in The California Islands: Proceedings of a Multidisciplinary Symposium, ed. Power, D.M. (Santa Barbara Museum of Natural History, Santa Barbara, CA).
28. Tan, A.-M. & Wake, D.B. (1995) Mol. Phyl. Evol. 4, 383–394.
29. Martin, B.D. & Emery, K.O. (1967) Am. Assoc. Pet. Geol. Bull. 51, 2281–2304.
30. Powell, R.E. & Weldon II, R.J. (1992) Annu. Rev. Earth Planet. Sci. 20, 431–468.
31. Highton, R. (1989) Ill. Biol. Monogr. 57, 1–78.