MANOS, PAUL S.*, ALICE M. STANFORD, AND MICHAEL J. SANDERSON. Department of Botany, Duke University, Durham, NC 27708, Division of Science & Math. University of the Virgin Islands, 2 John Brewers Bay, St. Thomas, VI 00802, and Section of Evolution and Ecology, University of California, Davis, CA 95616. - Phylogenetic patterns of disjunct Fagales: tracking the history of north temperate and subtropical forests.
An improved understanding of the phylogenetic history of the Fagaceae
and Juglandaceae, two widespread members of the expanded Fagales
clade, suggests several patterns of vicariance throughout the Tertiary
of the Northern Hemisphere. The rich fossil record for these families
also provides essential temporal data for calibrating phylogenies and
comparing divergence times times among apparently similar patterns of
vicariance. At least 4 genera of Fagaceae (Castanea,
Fagus, Lithocarpus and Quercus) and two genera of
Juglandaceae (Carya and Juglans) have disjunct
distributions amenable to biogeographical analysis. Fagaceae show a
successional pattern of discontinuity, perhaps starting with an
ancient disjunction within Trigonobalanuss.l. More
species-rich genera such as Fagus, Quercus, and
Lithocarpuscontinue to support a center of origin in south east
Asia with subsequent migration to western North America. Disjunction
within the evergreen genus Lithocarpus(SE Asia-W N. Amer.) may
suggest an exchange during warmer periods of the Eocene. In contrast,
a close relationship between Fagus grandifolia(NA) and south
east Asian species rather than Eurasian species supports a deciduous
connection via the Bering Land Bridge. Fossil data also confirm the
presence of Fagus in the Miocene of western North America. More
recent connections, possibly via the Bering Land Bridge, but with the
reverse pattern of migration, are indicated by the trans-continental
white oaks (Quercussect. Quercuss.s.). For
Juglandaceae, disjunctions within Caryaand Juglansappear
to have occurred at different times: Caryashows no evidence of
trans-continental disjunction at the sectional level, whereas
Juglansshows one recent example within the butternut species
group. In order to temporally discriminate among apparently similar
vicariant patterns, divergence times were calculated with maximum
likelihood methods that assume a molecular clock and alternative
methods that permit constrained rate variation. Randomization tests
were used to assess confidence intervals on divergence times,
permitting rigorous tests of the sequence of biogeographic events.
Key words: biogeography, divergence times, Fagaceae, Fagales, Juglandaceae, vicariance