Stephen G. Tilley
Myra M. Sampson Professor Emeritus of Biological Sciences
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Stephen G. Tilley earned his Ph.D. from the University of Michigan.
My research has been concerned with how populations undergo genetic differentiation and evolve toward becoming different species, and with asking what species of animals actually are.
My research colleagues, including several Smith College students, have dealt primarily with "dusky salamanders" of the genus Desmognathus, a group that is restricted to eastern North America and achieves its highest diversity in the southern Appalachian Mountains. Characters that humans can readily perceive and measure, such as behavior, color, shape and size, seem to evolve very slowly in these creatures. Different forms can thus be genetically distinct and reproductively isolated while being morphologically extremely similar. Our studies, using both starch gel electrophoresis and nucleic acid sequencing, have revealed that what were once thought to be single species of Desmognathus are, in fact complexes of forms that have undergone considerable genetic differentiation. Since 1996 our work has led to the partitioning of Desmognathus ochrophaeus into a complex of five species, including two new forms: Desmognathus orestes and Desmognathus abditus.
Tilley, S. G., and M. J. Mahoney. 1996. "Patterns of genetic differentiation in salamanders of the Desmognathus ochrophaeus complex (Amphibia: Plethodontidae)." Herpetol. Monogr. 10: 1–42.
Mead, L. S., and S. G. Tilley. 2000. "Ethological isolation and variation in allozymes and dorsolateral pattern between parapatric forms in the Desmognathus ochrophaeus complex." Ch. 8, pp. 181–198 in The Biology of Plethodontid Salamanders, R. C. Bruce, R. G. Jaeger, and L. D. Houck, eds. Kluwer Academic, Plenum Publishers.
Tilley, S. G. 2000. "Systematics of Desmognathus imitator." Ch. 5, pp. 121–147 in The Biology of Plethodontid Salamanders, R. C. Bruce, R. G. Jaeger, and L. D. Houck, eds. Kluwer Academic, Plenum Publishers.
Tilley, S. G., and J. E. Huheey. 2001. "Reptiles and Amphibians of the Smokies." Great Smoky Mountains Natural History Association.
Mead, L. S., S. G. Tilley, and L. A. Katz. 2002. "Genetic structure of the Blue Ridge dusky salamander (Desmognathus orestes): Inferences from allozymes, mitochondrial DNA and behavior." Evolution 55: 2287–2302.
Anderson, J., and S. G. Tilley. 2003. "Systematics of the Desmognathus ochrophaeuscomplex in the Cumberland Plateau of Tennessee." Herpetological Monographs, 17: 75–110.
Tilley, S. G., R. L. Eriksen, and L. A. Katz. 2008. "Systematics of dusky salamanders, Desmognathus (Caudata: Plethodontidae), in the mountain and Piedmont regions of Virginia and North Carolina, USA." Zoological Journal of the Linnaean Society 152: 115–30.
Tilley, S.G, J. Bernardo, L. A. Katz, L. Lopez, J. D. Roll, R. L. Eriksen, J. Kratovil, N. K. J. Bittner, and K. A. Crandall. 2013. “Failed species, innominate forms, and the vain search for species limits: Cryptic diversity in dusky salamanders (Desmognathus) of eastern Tennessee.” Ecology and Evolution 3: 2547-2567. http://onlinelibrary.wiley.com/doi/10.1002/ece3.636/full
Tilley, S.G. 2016. “Patterns of genetic differentiation in woodland and dusky salamanders.” Copeia, 2016:8-20.