BALDWIN, BRUCE G. Jepson Herbarium and Department of Integrative Biology, University of California, Berkeley, CA 94720. - Phylogeography and major range disjunctions of the rare, granite endemic Carlquistia muirii (Compositae—Madiinae): Ancient long-distance dispersal or surfing on the Salinian Block?
Phylogeography of the rare, perennial, Californian tarweed
Carlquistia [Raillardiopsis] muirii was studied
to assess whether range disjunctions in the southern Sierra Nevada and
between the Sierra Nevada and South Coast Ranges (Ventana Double Cone,
Monterey Co.) are best explained by long-distance dispersal or
vicariance. Occurrence of C. muirii, a granite endemic,
on Ventana Double Cone in the Santa Lucia Range, ca. 240 km from the
nearest Sierran population, is intriguing in part because granitic
exposures are extremely limited between the southern Sierra/Tehachapi
region and the northern Santa Lucia Range/Gabilan Range and unexposed
granitics are covered by sediments of at least Miocene age. Vicariance
could explain most of the Sierra/Santa Lucia disjunction, even without
assuming past occurrence of C. muirii off of granitics,
if the species existed ca. 5 Ma, when the Santa Lucia/Gabilan region
was juxtaposed with the Sierra/Tehachapi region. Any populations then
extending from the Sierra/Tehachapi onto Santa Lucia/Gabilan granitics
could have been transported in situ 240 km northwesterly by tectonic
slippage of the Salinian Block along the San Andreas Fault.
Phylogenetic analysis of 18S-26S rDNA ETS and ITS variation from
populations throughout the distribution of C. muirii
yielded a robust, well-resolved tree that is congruent with the area
cladogram for the southern Sierra Nevada and South Coast Ranges and
with the hypothesis that vicariance explains distributional patterns
in C. muirii. However, a calibrated, rate-constant rDNA
tree for perennials of the "Madia lineage" yields an
estimated time of divergence between Sierran and Santa Lucian
populations of only ca. 1 Ma, in conflict with a vicariance
hypothesis. Patterns of ancient, long-distance dispersal mimicking
vicariance may explain at least part of the fascinating phylogeography
of C. muirii.
Key words: Carlquistia muirii, Compositae, dispersal, phylogeography, vicariance