Unveiling the origin of Quercus serrata subsp. mongolicoides found in Honshu, Japan, by using genetic and morphological analyses

Abstract

Quercus mongolica is a tree found in temperate deciduous forests in east Asia. In Japan, Q. mongolica var. crispula is commonly found; moreover, an oak whose morphology is similar to that of Q. mongolica var. mongolica of the Asian continent has been found in certain areas of Honshu and Hokkaido. Recently, the oak found in Honshu was described as Q. serrata subsp. mongolicoides (QSM). However, genetic comparison between this oak and Q. mongolica var. mongolica of the Asian continent has not been performed; the origin of QSM is thus unknown. Therefore, we aimed to determine the origin of QSM by conducting nuclear microsatellite (nSSR), chloroplast DNA (cpDNA) and leaf morphology analyses for the three taxa, as well as other congeners. The cpDNA variation overlapped among the three taxa, suggesting low discrimination ability for these taxa. Although morphological congruency was found between QSM and Q. mongolica var. mongolica, results of nSSR analyses showed that QSM contained a genetic admixture of Q. mongolica var. mongolica of the Asian continent and Q. mongolica var. crispula of Japan, bolstering an admixture hypothesis. The nSSR and cpDNA analyses suggested that Q. mongolica var. crispula can be the progenitor of Q. mongolica var. mongolica and harbors the ancestral cpDNA haplotypes. Therefore, we concluded that QSM might have been created by an admixture that likely occurred within Japan between Q. mongolica var. crispula and putative relict Q. mongolica var. mongolica, which might have diverged in or around Japan from Q. mongolica var. crispula during the late Pleistocene.

Contact zone of two different chloroplast lineages and genetic guidelines for seed transfer in Quercus serrata and Quercus crispula

“…According to the phylogeographic structures of the species previously inferred from analyses of cpDNA variation, each of them has two distinct lineages, in the northeast and southwest regions of central Japan, separated by major mountains (Kanno et al, 2004; Okaura, Quang, Ubukata, & Harada, 2007; San Jose‐Maldia et al, 2017). Oak species are also closely related and interspecific hybrids are frequently found in some specific environments (Aizawa et al, 2018; Matsumoto et al, 2009). Thus, the same cpDNA haplotypes are shared between closely related hybridizing oak species (Petit et al, 1997; Ramos‐Ortiz, Oyama, Rodríguez‐Correa, & González‐Rodríguez, 2016; Whittemore & Schaal, 1991).…”

Environment‐dependent introgression from Quercus dentata to a coastal ecotype of Quercus mongolica var. crispula in northern Japan

“…The coastal Qc ecotype is recognized as a Qc population in the coastal environment in northern Hokkaido, which is genetically admixed with Qd and is phenotypically similar to Qd (Ohba, ; Aizawa et al ., ; Nagamitsu et al ., ). This study confirms these properties quantitatively based on genome‐wide genotypes, multitrait phenotypes, and coastal stress.…”

“…In northern Hokkaido, the northernmost part of Japan, Qd trees are rare because this region is beyond the northern distributional limit of Qd . In the region, a coastal Qc ecotype with unique traits, which are similar to Qd phenotypes and are associated with tolerance to coastal stress, occurs in the coastal area (Aizawa et al ., ). Some taxonomists regard the coastal Qc ecotype as a putative hybrid between Qc and Qd (Ohba, ).…”

Intraspecific genetic divergence of the subalpine shrubby variety Quercus crispula var. horikawae from the mountain tree variety Q. crispula var. crispula in Japan

“…In central Honshu, Q. mongolica var. mongolicoides (H. Ohba) M. Aizawa is thought to originate from ancient hybridization between Q. crispula and Q. mongolica , the latter of which had probably colonized the Japanese Archipelago during glacial cycles (Aizawa et al, 2018; Aizawa et al, 2021). In the continental northwestern Asia, Q. mongolica var.…”