Phylogeny and genetic variation of Fagaceae in tropical montane forests

Abstract

Phylogenetic relationships of evergreen Fagaceae species mainly distributed in Japan and Malaysia were examined based on chloroplast DNA sequences. In the genus Castanopsis and Lithocalpus, Japanese and Malaysian species formed separate clusters, but are monophyletic. Whereas for the Quercus subgenus Cyclobalanopsis, Japanese and Malaysian species clustered in separate groups and were not monophyletic. The Southeast Asian endemic species Trigonobalanus verticillata maintained a large inter-populational genetic variation which is similar to the level among species within genus, suggesting it was isolated for a long time in primitive state. The molecular clock approach showed that intra-generic diversifications between the monophyletic groups of Japanese and Malaysian taxa within Castanopsis, Lithocarpus and Cyclobalanopsis occurred by 22 - 17 MYA (Early to Middle Miocene). The distinct phylogenetic patterns between Japanese and Malaysian taxa suggest that the temperate to tropical disjunction in Asia might be the result of the long-term isolation of these evergreen genera, which was probably caused by the withdrawal and subdivision of the forests following the change to a moist and warm climate in Middle Miocene.