Abstract
Ecotypic divergence in tree taxa often occurs in sub-alpine habitats,
where environmental conditions are more stressful than those in lower
elevations. In the mountain oak species in Japan, Quercus
crispula (Qc ), the sub-alpine shrubby variety, Q.
crispula var. horikawae (Qch ), has been recognized in
central and northern Honshu. Although Qch has different
phenotypes from Qc , genetic divergence between Qc andQch has not been examined yet. Pairs of Qc and Qchpopulations in eight locations and additional Qc and Qchpopulations around these locations were investigated. Leaf size ofQch was smaller than that of Qc . Chloroplast DNA
haplotypes were shared between the Qc and Qch populations.
In genotypes at 29 nuclear microsatellite loci, genetic diversity did
not differ between the Qc and Qch populations. Principal
component analysis and a neighbor-joining tree of populations based on
microsatellite genotypes demonstrated that 13 Qc populations and
eight Qch populations were grouped separately, except for threeQch populations that were grouped to Qc . Climatic
conditions in the eight Qch populations were characterized by
lower temperature and heavier snowfall than those in the 16 populations
of the genetic group of Qc . These results suggest the genetic
divergence between Qc and Qch associated with sub-alpine
climatic conditions, irrespective of leaf size. The origin of the
sub-alpine Qch lineage and the history of ecotypic divergence
should be investigated in future genomic studies.