CANNON, CHARLES H.1,2* and PAUL S. MANOS1. 1Dept. of Biology, Duke University, Box 90339, Durham, NC 27708 U.S.A.; 2IBEC, University of Malaysia, Sarawak, Kota Samarahan 94300 Malaysia. - The molecular phylogeography of Lithocarpus (Fagaceae): limited migration and ancient persistence.
The stone oaks (Lithocarpus) form the largest genus (300 spp.)
in the insect-pollinated chestnut subfamily in the Fagaceae and
produce fruit with similar ecological characteristics as
Quercus acorns. These trees are largely restricted to mesic
habitats throughout much of Southeast Asia and have two centers of
diversity: Indochina and the island of Borneo. To investigate whether
current landscape level genetic variation might indicate historical
migration routes and refugia, we sequenced an intergenic region
(rbcL-atpBE) on the chloroplast genome from 166 individuals in eight
different locations. Our taxonomic sampling included 49 species in at
least eight sections to address the question of interspecific
introgression. We found 66 unique genotypes, which exhibited strong
phylogenetic and geographic structure. Two major lineages, one shared
between Indochina and Borneo ("continental") and one found
only on Borneo ("Bornean"), contained roughly equal numbers
of individuals. Numerous transpecific polymorphisms were observed and
only one species was fixed on a type, which was shared with other
species. In general, individuals from a single location were more
closely related than expected, indicating limited seed migration.
Populations found in the northwest part of the island possessed the
highest degree of overall diversity and appeared to lie nearest the
center of origin of the group. The presence of a shared ancestral
genotype between China and Borneo suggests limited genetic drift and
persistence of a neutral transpecific polymorphism through a time span
perhaps exceeding ten million years. A number of macroevolutionary
processes, acting simultaneously and at different times in the past,
are responsible for the observed patterns, including incomplete
lineage sorting, introgressive hybridization, local population
dynamics, and isolation by distance. Further sampling of the other
Southeast Asian landmasses will be necessary to pinpoint migration
routes and refugia and to calibrate the timing of these events.
Key words: Borneo, Fagaceae, interspecific phylogeography, Lithocarpus, Southeast Asia, transpecific polymorphisms