GEOGRAPHIC VARIATION IN ALLOZYMES IN A “RING SPECIES,” THE PLETHODONTID SALAMANDER ENSATINA ESCHSCHOLTZII OF WESTERN NORTH AMERICA

Abstract

The ring species Ensatina eschscholtzii (a plethodontid salamander) of western North America has a circle of subspecies surrounding the Central Valley of California which come into contact and are sympatric in southern California. We examined 26 proteins in 19 populations (maximum of 10 specimens per population) collected throughout the range in order to gain an understanding of the degree of differentiation in the group. Allozymic differentiation is profound, with genetic distances in excess of 0.5 (Rogers or Nei) between populations. Naturally hybridizing populations differ by genetic distances greater than 0.4. Two general classes of color morphs, blotched and unblotched, are segregated geographically, but they do not form discrete genetic units. Both are deeply differentiated, and genetic distances among populations of either class exceed those measured between the classes where they are sympatric in southern California. This study disclosed little evidence of gene exchange around the ring of populations and sampling of many additional populations in regions between populations sampled thus far will be required to determine whether smooth intergradation occurs. Although genetic distances measured exceed those between some co-occurring species of plethodontid salamanders, we find no evidence of borders between cryptic species.

Falling apart and merging: diversification of slender salamanders (Plethodontidae: Batrachoseps) in the American West

“…1). A similar pattern of dispersal was postulated for another terrestrial plethodontid salamander, Ensatina eschscholtzii xanthoptica (Stebbins, 1949), and is supported by genetic evidence (Wake & Yanev, 1986;Moritz et al, 1992). At its southern extreme in the Sierra Nevada, B. attenuatus overlaps with a relictus group lineage, B. diabolicus.…”

GENETIC LEAKAGE AFTER ADAPTIVE AND NONADAPTIVE DIVERGENCE IN THEENSATINA ESCHSCHOLTZIIRING SPECIES

“…Starch-gel electrophoresis was used to examine protein variation in the samples for 27 allozyme loci, following the methods of Wake and Yanev (1986). Due to the high genetic variability of this system, by adjusting the electrophoretic conditions we captured the maximum number of alleles per region.…”

“…The Ensatina eschscholtzii complex is a textbook example of a ring species that illustrates the role of geography in species formation (Dobzhansky 1958;Futuyma 1998;Dawkins 2004). The ancestor is hypothesized to have expanded from northern California around the inhospitable habitat that currently constitutes the Central Valley, gradually diverging along each arm of expansion (Stebbins 1949;Wake and Yanev 1986). When populations met at the terminus, in southern California, species-level divergence has occurred and they overlap with full reproductive isolation or rare hybridization (Wake et al 1989).…”

The Evolutionary Response of Predators to Dangerous Prey: Hotspots and Coldspots in the Geographic Mosaic of Coevolution Between Garter Snakes and Newts

“…Another piece of suggestive evidence is the high level of resistance around San Francisco Bay and in the Omo population in El Dorado Co., California. Genetic studies in other reptiles (Feldman 2000) and amphibians (Wake and Yanev 1986;Moritz et al 1992) suggest a migration corridor in the Central Valley (a ''trans-valley leak''; Rodriguez-Robles et al 2001) through which gene flow occurs between the central Sierra Nevada and coastal California. If similar patterns of gene flow occur in T. sirtalis, they could be at least partially responsible for the extreme resistance (Level VIII) observed at Omo.…”