Macroevolutionary and phylogeographic studies of Lithocarpus (Fagaceae): Gene flow and morphological evolution in a tropical tree.

摘要

The tropical evergreen trees in the genus Lithocarpus are unusual in the oak family because of their insect pollination system. They produce single-seeded nuts, like oaks (Quercus), but across a broader morphological spectrum. They codominate submontane habitats and appear at low densities and diversities in other habitats. Current and historical patterns of phenotypic and genetic variation were explored in eight separate populations. Extensive field collections were made and comprehensive herbarium surveys were conducted. A new species was described and a discussion of one major section provided (Chapter One). Shape analysis of internal fruit morphology distinguished two major fruit types: the classic "acorn" and the specialized "ER". Phenotypic transformation series were estimated using maximum likelihood techniques. These transformation series were combined and compared with nuclear DNA sequence using multiple phylogenetic reconstruction techniques (Chapters Two and Three). Little modification of fruit morphology between the ingroup and outgroup taxa suggested great evolutionary stability, while the transition to the ER fruit type occurred in two separate lineages, suggesting convergent evolution. Molecular and morphometric divergence were decoupled in the transition between the two fruit types, i.e. large morphological change with little molecular change.;Chloroplast sequence data from 166 individuals of numerous species were analyzed to examine patterns of migration, introgression, and population dynamics (Chapter Four). The resulting genetic network contained two major lineages, one shared between the mainland and Borneo while the other was endemic to the island. Strong geographic and phylogenetic structure were found, suggesting limited migration and abundant diversification within locations. An ancient genotype, exceeding ten million years in age, existed unmodified on both landmasses, suggesting limited genetic drift. Northwest Borneo was close to the center of origin for the genus, which probably lay on greater Sundaland. Two scenarios for the Bornean lineage can be postulated: (1) reinvasion from the mainland or (2) diversification in the unsampled central mountain range. Post-hoc hypothesis tests, stratified by location and taxonomy and using various parameters of migration and extinction, were outlined and the most general cases were performed.