David B. Wake and Kay P. Yanev,
Geographic variation in allozymes in a 'ring species,'
the plethodontid salamander Ensatina eschscholtzi of western North
Evolution 40(4),1986,pp 702-715
More information available on Ensatina
The ring species Ensatina eschscholtzi (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.
Allozyme 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. (see Genetic
distances map Two general classes of color morphs, blotched and unblotched,
are segregated geographically, but they do not form discreet 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 distances measured
exceed those between some co-occurring species of plethodontid salamanders,
we find no evidence of borders between cryptic species.
Genetic distances map