David B. Wake, 1997
Incipient species formation in salamanders of the Ensatina
Proc. Natl. Acad. Sci., Vol.94, pp. 7761-7767.
The Ensatina eschscholtzii complex of plethodontid salamanders,
a well known "ring species", is thought to illustrate stages
in the speciation process. Early research, based on morphology and coloration,
has been extended by the incorporation of studies of protein variation
and mitochondrial DNA sequences. The new data show that the complex includes
a number of geographically and genetically distinct components that are
at or near the species level. The complex is old, and apparently has undergone
instances of range contraction, isolation, differentiation, and then expansion
and secondary contact. While the hypothesis that speciation is retarded
by gene flow around the ring is not supported by molecular data, the general
biogeographical hypothesis is supported. There is evidence of a north
to south range expansion along two axes, with secondary contact and completion
of the ring in Southern California.Current research
targets regions once thought to show primary intergradation, but which
molecular markers reveal to be zones of secondary contact. Here emphasis
is on the subspecies xanthoptica , which
is involved in four distinct secondary contacts in central California.
There is evidence of renewed genetic interactions upon recontact, with
greater genetic differentiation within xanthoptica than between
it and some of the interacting populations. The complex presents a full
array of intermediate conditions between well marked species and geographically
variable populations. Geographically differentiated
segments represent a diversity of depths of time of isolation and admixture,
reflecting the complicated geomorphological history of California. Ensatina
illustrates the continuing difficulty in making taxonomic assignments
in complexes studied during species formation.
See early distribution
of Ensatina 5,000,000 years ago.
text of publication
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