Genetic Differentiation and Genetic Diversity of Castanopsis (Fagaceae), the Dominant Tree Species in Japanese Broadleaved Evergreen Forests, Revealed by Analysis of EST-Associated Microsatellites

Abstract

The broadleaved evergreen forests of the East Asian warm temperate zone are characterised by their high biodiversity and endemism, and there is therefore a need to extend our understanding of its genetic diversity and phylogeographic patterns. Castanopsis (Fagaceae) is one of the dominant tree species in the broadleaved evergreen forests of Japan. In this study we investigate the genetic diversity, genetic structure and leaf epidermal morphology of 63 natural populations of C. sieboldii and C. cuspidata, using 32 Expressed Sequence Tag associated microsatellites. The overall genetic differentiation between populations was low (G ST = 0.069 in C. sieboldii and G ST = 0.057 in C. cuspidata). Neighbor-joining tree and Bayesian clustering analyses revealed that the populations of C. sieboldii and C. cuspidata were genetically clearly differentiated, a result which is consistent with the morphology of their epidermal cell layers. This suggests that C. sieboldii and C. cuspidata should be treated as independent species, although intermediate morphologies are often observed, especially at sites where the two species coexist. The higher level of genetic diversity observed in the Kyushu region (for both species) and the Ryukyu Islands (for C. sieboldii) is consistent with the available fossil pollen data for Castanopsis-type broadleaved evergreen trees during the Last Glacial Maximum and suggests the existence of refugia for Castanopsis forests in southern Japan. Within the C. sieboldii populations, Bayesian clustering analyses detected three clusters, in the western and eastern parts of the main islands and in the Ryukyu Islands. The west-east genetic differentiation observed for this species in the main islands, a pattern which is also found in several plant and animal species inhabiting Castanopsis forests in Japan, suggests that they have been isolated from each other in the western and eastern populations for an extended period of time, and may imply the existence of eastern refugia.

Species diversity of insects in Japan: Their origins and diversification processes

“…The relationship between acorn weevils and their host plants represents such an example. The distribution ranges and the population genetic structures of the acorn weevils (Coleoptera: Curculionidae), Curculio sikkimensis (Heller, 1927) and Curculio hilgendorfi (Harold, 1878), correspond very well with those of their laurel host plants, Castanopsis sieboldii and Castanopsis cuspidate , respectively (Aoki et al , , ). Modeling suggests that they were forced to the south and contracted their distribution ranges during glacial periods, but that they were forced to the north and expanded their distribution ranges during interglacial periods.…”

“…Such a high species diversity of Japanese plants, as well as the insect diversity, should be owed to various physical factors of location, climate, geography and geology of the Japanese Islands (Kubota et al ). In addition, insect‐plant coevolution would have enhanced speciation in some insect groups (Toju ; Azuma et al ; Aoki et al , ; Kusumi et al ).…”

Genetic diversity of Ceratoides arborescens, a species endemic to China, detected by inter-simple sequence repeat (ISSR)

“…Previous studies have shown that endemic species and species with narrow distribu-tion usually show lower levels of genetic diversity than widespread species (Tanahara and Maki, 2010;Chen et al, 2013;Duan et al, 2013;Nguyen et al, 2013;Aoki et al, 2014). However, C. arborescens was found to possess an unexpectedly high rate of genetic diversity (Table 3), indicating the species ability to adapt to varying environmental conditions.…”

Biogeographic patterns of ectomycorrhizal fungal communities associated withCastanopsis sieboldiiacross the Japanese archipelago

“…et Mashiba (Fagaceae). We chose C. sieboldii as the focal host species because this species is widely distributed across different climate regions of the Japanese archipelago and its phylogeographic pattern over its distribution range has been already documented with genetic markers (Aoki et al , 2014). Importantly, unlike Europe and North America, ice sheets were not present in the Japanese archipelago during the Quaternary period, and this, together with the complex mountainous terrain of Japan, resulted in the establishment of tree refugia in multiple regions across Japan (e.g.…”

“…Tsukada, 1984). Therefore, the present distributions of individual genotypes of single species are assumed to reflect the environmental gradients like climate (Tsukada, 1984; Aoki et al , 2014). For these features, we considered C. sieboldii in Japan as the appropriate host species to evaluate the effect of host genotypes and genotypic diversity on the geographic distribution of the associated ECM fungal community.…”