Genetic divergence of the sub-alpine shrubby variety, Quercus crispula
var. horikawae, from the mountain oak species, Q. crispula, in Japan
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 and Qch has
not been examined yet. Pairs of Qc and Qch populations in eight
locations and additional Qc and Qch populations around these locations
were investigated. Leaf size of Qch 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 three Qch
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.