Research information on Mitochondrial
Craig Moritz, Christopher J. Schneider,
and David B. Wake, 1992.
Evolutionary relationships within the Ensatina
eschscholtzii complex confirm the ring species interpretation.
Systematic Biology 41(3),1992,pp 273-291
More information available
on Ensatina eschscholtzi:
Sequences (644-681 bp) from the mitochondrial cytochrome b
gene were obtained for 24 individuals representing the geographic
range and morphological diversity of the polytypic salamander ring
species Ensatina eschscholtzii. These data were
used to estimate the phylogeny of components of the ring to test the
biogeographic scenario underlying current interpretations of speciation
in this complex. The analysis revealed high levels of nucleotide
variation among subspecies. Strong subdivision was evident within
the subspecies platensis and oregonensis.
The phylogenetic hypothesis of minimum length that is best supported
by the data contains one monophyletic group that includes populations
from the southern Sierra Nevada and mountains of southern California
(croceater, klauberi and southern platensis)and
another that includes populations of southern and central coast regions
(xanthoptica and eschscholtzii). Samples of
oregonensis were typically basal, but their precise branching
order was unstable. Both oregonensis and platensis
were paraphyletic, with several disparate lineages in oregonensis
and a strong north-south dichotemy in platensis. The
data were incompatible with a biogeographic model that required all
subspecies to be monophyletic but were compatible with slightly modified
predictions of a model assuming stepwise colonizations from north
to south down the Sierra Nevada and independently down the coast ranges.
These features provide strong support for the biogeographic scenario
central to the interpretation of Ensatina eschscholtzii as
a ring species. Division of this complex into separate species
on the basis of the observed patterns of monophyly for mitochondrial
DNA (mtDNA) is unwarrented because further sampling could reveal additional
instances of paraphyly across subspecies and, more generally, because
mtDNA alone should not be used to infer species boundries.