Molecular analysis of genetic diversity in natural populations of beech species

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The amount and distribution of mitochondrial (mt) DNA restriction fragment length polymorphism was determined among individual tree samples of two Japanese beech species, Fagus crenata and F.japonica. Individual plants were collected from 16 F.crenata populations throughout the range of the species, and from three F.japonica populations. We detected enough variation to characterize eleven and three chondriome types in F.crenata and F.japonica, respectively. The grouping of beech chondriome types based upon the cladistic analysis of mtDNA polymorphism allowed us to recognize the apparent geographical patterns of mtDNA diversity : the resulting three main groups occupied distinct geographic areas. This geographic differentiation is likely to reflect the history of the Japanese beech forests after the last glacial period of the Pleistocene. In addition, the mtDNA polymorphism encountered within F.crenata encompassed all the variation observed in F.japonica. Our result suggests the need for re-evaluation of their phylogenetic relationships.MtDNA restriction fragment length polymorphisms were also used to examine cytoplasmic diversity within a relic-like population of F.hayatae, located in northern Taiwan. The analysis failed to reveal any polymorphisms, an observation that suggests cytoplasmic uniformity in the F.hayatae population examined. It is also interesting to note that the chondriome type of our F.hayatae samples is very close to that characteristic of F.crenata populations in the southernmost area of Japan.