DIFFERENTIATION OF MITOCHONDRIAL DNA POLYMORPHISMS IN POPULATIONS OF FIVE JAPANESE ABIES SPECIES

Mitochondrial DNA polymorphism of 40 populations of five Abies species was investigated using PCR-amplified coxI and coxIII gene probes. Using four combinations of probe and restriction enzyme, we detected three major haplotypes and 15 total haplotypes. We also found varied levels of gene diversity for the different species: 0.741, 0.604, 0.039, 0.000, and 0.292 for A. firma, A. homolepis, A. veitchii, A. mariesii, and A. sachalinensis, respectively. The marginal and southern populations of A. firma and A. homolepis have unique haplotypes, especially the Kyushu, Shikoku, and Kii Peninsula populations, which inhabit areas coinciding with probable refugia of the last glacial period and possess high levels of mtDNA genetic diversity. The haplotypes in some populations suggested mtDNA capture also occurred between species through introgression/hybridization. The strong mtDNA population differentiation in Abies is most likely due to the maternal inheritance of mitochondria and restricted seed dispersal. A phenetic tree based on the genetic similarity of the mtDNA suggests that some species are polyphyletic. Based on mtDNA variation, the five Abies species could be divided roughly into three groups: (1) A. firma and A. homolepis, (2) A. veitchii and A. sachalinensis, and (3) A. mariesii. However, we found that all these Abies species, except A. mariesii, are genetically very closely related according to an analysis of their cpDNA sequences. This showed that the chloroplast rbcL gene differed by only one base substitutions among the four species. We believe that the mtDNA variation and cpDNA similarity clearly reflect relationships among, and the dissemination processes affecting these Abies species since the last glacial period.