渡辺 洋一

<tt>園芸植物として利用されるアジサイは、その野生種であるガクアジサイを含めいくつかの異なる花型が知られている。その中でも手まり咲き型の園芸品種は野生には見られない特徴的な花型として多く植栽されている。しかし、この手まり咲き型は静岡県伊豆半島東部の城ヶ崎海岸において野生型の個体と同所的に見られ、この花型が自生である可能性が考えられる。この仮説を検証するために</tt>MIG-seq <tt>法を用いた一塩基多型（</tt>SNPs<tt>）の検出を行い、伊豆半島の石廊崎および伊豆諸島の神津島の自生個体も加えた遺伝解析を行った。検出された</tt>281 SNPs<tt>を用いて解析を行った結果、神津島と伊豆半島の集団は明瞭に区別でき、伊豆半島の城ヶ崎海岸と石廊崎集団はゆるやかには区別できた。 城ヶ崎海岸の野生型と手まり咲き型を含む変わり咲き型はヘテロ接合度の期待値に差が見られず、遺伝的関係は高い類似性を示した。加えて、城ヶ崎海岸内において地理分布と遺伝的類似性は弱い空間自己相関を示した。これらの結果から、城ヶ崎海岸の手まり咲き型の個体は自生であると考えられ、重要な遺伝的資源として保全の重要性が高いと</tt><tt>言える。 </tt>

Tree form evolution is an important ecological specialization for woody species, but its evolutionary process with adaptation is poorly understood, especially on the microevolutionary scale. Daphniphyllum macropodum comprises two varieties: a tree variety growing in a warm temperate climate with light snowfall and a shrub variety growing in a cool temperate climate with heavy snowfall in Japan. Chloroplast DNA variations and genome-wide single-nucleotide polymorphisms across D. macropodum populations and D. teijsmannii as an outgroup were used to reveal the evolutionary process of the shrub variety. Population genetic analysis indicated that the two varieties diverged but were weakly differentiated. Approximate Bayesian computation analysis supported a scenario that assumed migration between the tree variety and the southern populations of the shrub variety. We found migration between the two varieties where the distributions of the two varieties are in contact, and it is concordant with higher tree height in the southern populations of the shrub variety than the northern populations. The genetic divergence between the two varieties was associated with snowfall. The heavy snowfall climate is considered to have developed since the middle Quaternary in this region. The estimated divergence time between the two varieties suggests that the evolution of the two varieties may be concordant with such paleoclimatic change.

PREMISE: The formation of isolated montane geography on islands promotes evolution, speciation, and then radiation if there are ecological changes. Thus, investigating evolutionary histories of montane species and associated ecological changes may help efforts to understand how endemism formed in islands' montane floras. To explore this process, we investigated the evolutionary history of the Rhododendron tschonoskii alliance, which grows in montane environments of the Japanese archipelago and the Korean Peninsula. METHODS: We studied the five species in the R. tschonoskii alliance and 30 outgroup species, using genome-wide single-nucleotide polymorphisms and cpDNA sequences, in association with environmental analyses. RESULTS: The monophyletic R. tschonoskii alliance diverged since the late Miocene. Species in the alliance currently inhabit a cold climatic niche that is largely different from that of the outgroup species. We observed clear genetic and niche differentiations between the taxa of the alliance. CONCLUSIONS: The association of the alliance's evolution with the formation of cooler climates on mountains indicates that it was driven by global cooling since the mid-Miocene and by rapid uplift of mountains since the Pliocene. The combination of geographic and climatic isolation promoted high genetic differentiation between taxa, which has been maintained by climatic oscillations since the Quaternary.

Evolutionary radiation is a widely recognized mode of species diversification, but its underlying mechanisms have not been unambiguously resolved for species-rich cosmopolitan plant genera. In particular, it remains largely unknown how biological and environmental factors have jointly driven its occurrence in specific regions. Here we use Rhododendron, the largest genus of woody plants in the Northern Hemisphere, to investigate how geographic and climatic factors, as well as functional traits, worked together to trigger plant evolutionary radiations and shape the global patterns of species richness based on a solid species phylogeny. Using 3437 orthologous nuclear genes, we reconstructed the first highly supported and dated backbone phylogeny of Rhododendron comprising 200 species that represent all subgenera, sections, and nearly all multi-species subsections, and found that most extant species originated by evolutionary radiations when the genus migrated southwards from circumboreal areas to tropical/subtropical mountains, showing rapid increases of both net diversification rate and evolutionary rate of environmental factors in the Miocene. We also found that the geographically uneven diversification of Rhododendron led to a much higher diversity in Asia than in other continents, which was mainly driven by two environmental variables, i.e., elevation range and annual precipitation, and were further strengthened by the adaptation of leaf functional traits. Our study provides a good example of integrating phylogenomic and ecological analyses in deciphering the mechanisms of plant evolutionary radiations, and sheds new light on how the intensification of the Asian monsoon has driven evolutionary radiations in large plant genera of the Himalaya-Hengduan Mountains.

Plants growing in similar climates with extensively overlapping distributions may exhibit similar phylogeographic patterns, due to similarities in range shifts during past climatic oscillations. We tested and exploited this expectation in a comparison of the evolutionary and demographic histories of two related and co-distributed species endemic to Japan-Rhododendron pentaphyllum and R. quinquefolium. Genetic variation in sequences of noncoding chloroplast DNA regions and hundreds of nuclear single nucleotide polymorphisms were used to investigate 191 individuals from 13 populations of R. pentaphyllum and 142 individuals from 10 populations of R. quinquefolium. We found that the two species were not each other's closest relative, and we found different times to the most recent common ancestor of extant populations based on both chloroplast DNA and nuclear SNPs. Rhododendron pentaphyllum exhibited higher genetic variation between populations than R. quinquefolium, while the two species had similar patterns of genetic divergence between regions with slightly different divergence times. These lines of evidence suggest that the similar ranges of the two species are the result of repeated range shifts since speciation during climatic oscillations.

Geographic and environmental isolations of islands and the mainland offer excellent opportunity to investigate colonization and survival dynamics of island populations. We inferred and compared evolutionary processes and the demographic history of Rhododendron tsusiophyllum, in the Izu Islands and the much larger island Honshu, treated here as the mainland, using thousands of nuclear SNPs obtained by ddRAD-seq from eight populations of R. tsusiophyllum and three populations of R. tschonoskii as an outgroup. Phylogenetic relationships and their habitats suggest that R. tsusiophyllum had evolved and migrated from cold north to warm south regions. We detected clear genetic divergence among populations in three regions of Honshu and the Izu Islands, suggesting restricted migration between them due to isolated habitats on mountains even in the mainland. The three regions have different changes in effective population size, especially, genetic diversity and population size of the Izu Islands are small compared to the others. Further, habitats of populations in the Izu Islands are warmer than those in Honshu, suggesting that they have undergone adaptive evolution. Our study provides evidences of montane rather than insular isolation on genetic divergence, survival of populations and significance of adaptive evolution for island populations with small population size and low genetic diversity, despite close proximity to mainland populations.

Three new taxa, Rhododendron sohayakiense Y.Watan. & T.Yukawa (Ericaceae), and its two varieties, var. kiusianum Y.Watan., T.Yukawa & T.Minamitani and var. koreanum Y.Watan. & T.Yukawa are described and illustrated from Japan and South Korea. They can be distinguished from each other and from the other members of the R. tschonoskii alliance, i.e. R. tschonoskii, R. tetramerum, R. trinerve and R. tsusiophyllum, through their combination of leaf size, leaf morphologies including lateral nerves on abaxial leaf surface, corolla morphologies including number of corolla lobes, style length and anther form. Phylogenetic inferences based on chloroplast DNA and genome-wide sequences revealed that each of the three new taxa is monophyletic and they further form a clade. Distributions of the three taxa are also clearly separated from each other and also from the other members of the R. tschonoskii alliance.

<p>現在日本に生育するイチョウは中国から伝来したものだが，日本各地に拡散された過程は明確でない。本研究では，樹齢が長く日本に伝来した当初に近い遺伝的特徴を維持していると考えられる各地のイチョウ巨木を対象とし，遺伝的変異の地域的特性から，日本におけるイチョウの伝播経路および伝播方法の推定を試みた。九州から本州東北部の胸高幹周8 m以上の巨木から葉を採取し，180個体199サンプルについて8つのマイクロサテライトマーカーを用いて解析を行った。解析の結果，8遺伝子座から8～21の対立遺伝子を検出し，142種類の遺伝子型が認識され，13種類の遺伝子型が70個体で共有されていた。遺伝子型を共有している個体はクローンであると考えられ，地理的に離れて分布している場合もあることから，日本におけるイチョウの伝播には種子だけでなく挿し木等の方法も用いられたと考えられる。遺伝的多様性を比較すると，遺伝子多様度（H_E）は0.57-0.82，アレリックリッチネス（AR）は4.51-8.49を示し，どちらも他地域に比べ東日本で低い値を示したため，中国から西日本にイチョウが伝来し，その一部が東日本に運ばれたと考えられる。</p>

Ecological speciation is an important factor in the diversification of plants. The distribution of the woody species Rhododendron indicum, which grows along rivers and is able to withstand water flow when rivers flood (i.e. it is a rheophyte), is disjunct, in contrast to the widespread distribution of its relative, Rhododendron kaempferi. This study aimed to elucidate the phylogenetic relationships between R. indicum and R. kaempferi and the evolutionary processes that gave rise to them. The sequences of three non-coding chloroplast DNA regions (total length 1977 bp) were obtained from 21 populations covering the ranges of the two species. In addition, genome-wide SNPs were genotyped from 20 populations using a genotyping by sequencing method. Leaf morphologies were measured for eight representative populations. Two chloroplast DNA haplotypes, which were detected in R. indicum, were shared between the two species. Genome-wide SNPs identified two lineages in R. indicum and these lineages did not constitute a monophyletic group. Each of these two lineages was related to geographically close populations of R. kaempferi. Leaf morphology, which is a characteristic feature in rheophytes, was not differentiated between the two lineages in R. indicum. The morphological similarity between the two heterogeneous lineages may be a result of parallel evolution from R. kaempferi or of introgressive hybridization between the species due to strong selective pressure imposed by flooding.

Simple sequence repeat (SSR) markers were developed from expressed sequence tags (ESTs) for Rhododendron section Brachycalyx in order to elucidate its evolutionary processes and reproductive ecology. Nineteen polymorphic EST-SSR markers were developed from EST libraries of R. amagianum and R. hyugaense. Polymorphisms for these markers were assessed using four species of section Brachycalyx. The number of alleles ranged from 1 to 14, and the observed and expected heterozygosity ranged from 0.000 to 0.931 and 0.000 to 0.904, respectively. The EST-SSR markers developed in this study will be useful for elucidating population genetic structure and breeding systems in section Brachycalyx.

AimTo reconstruct the diversification history of Rhododendron sect. Brachycalyx (Ericaceae), and to elucidate the differences in evolutionary history between 18 insular and two continental species.LocationIslands of Japan, South Korea and Taiwan and the mainland of China in East Asia.MethodsSequences of seven non-coding chloroplast DNA regions (3971bp) were obtained from 74 populations covering all 20 species in Rhododendron sect. Brachycalyx. The diversification history of the section was estimated by phylogenetic analysis and molecular dating. Genetic diversity estimates within species and species groups (continental and insular species) were calculated. Differences in patterns of genetic structure within each species group were estimated by analysis of the spatial genetic structure.ResultsThe section was monophyletic and started to diversify in the late Miocene or Pliocene. We detected 61 haplotypes in the section, of which 44 were observed in the insular species and 17 in the continental species. The two species groups were almost monophyletic. Genetic diversity across species was higher for the group of insular species than for the group of continental species, corresponding to the difference in species richness. In contrast, the insular species showed a tendency towards low genetic diversity within species and populations, whereas the continental species showed the opposite trend.Main conclusionsThe rapid diversification in the insular species during the Quaternary may be a result of genetic drift due to population isolation and population decline on the islands. In contrast, widespread migration or colonization may have prevented allopatric speciation in the continental species.

The morphological traits and genetic backgrounds of hybrid individuals in a hybrid zone reflect the history of that zone. In the hybrid zone between Rhododendron japonoheptamerum var. hondoense (RJH) and R. japonoheptamerum var. kyomaruense (RJK), flower morphological traits that can be used to distinguish the two varieties were measured and leaves were sampled for DNA extraction. Reference populations consisting of pure RJH and RJK were also used. Genotype data for individuals were obtained by the multiplexed ISSR genotyping by sequencing (MIG-seq) method. RJH and RJK in the reference populations were morphologically and genetically clearly differentiated. In the hybrid zone studied, although there were morphologically pure RJH and RJK, and hybrids between them, most individuals, including those that were morphologically pure, had ancestries from both RJH and RJK. There were no significant correlations between morphological traits and the proportion of ancestry within an individual. These results suggest that this hybrid zone originated from the hybridization between the RJH and RJK in the past. The result of model comparison among population demographic models also supported this hypothesis, and the time when the hybrid zone was established was estimated to be 410,000 years ago. It is considered that accumulation of recombinations subsequent to the formation of the hybrid zone contributed to the inconsistency between the morphological traits and the fraction of each ancestral genome within an individual.

Continental islands provide opportunities for testing the effects of isolation and migration on genetic variation in plant populations. In characteristic of continental islands is that the geographic connections between these islands, which are currently distinguished by seaways, have experienced fluctuations caused by sea-level changes due to climate oscillations during the Quaternary. Plant populations on the islands have migrated between these islands via the exposed seafloors or been isolated. Here, we examined the demographic history of a temperate shrub, Rhododendron weyrichii, which is distributed in the southwestern parts of the Japanese archipelago and on an island of South Korea, using statistical phylogeographic approaches based on the DNA sequences of two chloroplast and eight nuclear loci in samples analyzed from 18 populations on eight continental islands, and palaeodistribution modeling. Time estimates for four island populations indicate that the durations of vicariance history are different between these populations, and these events have continued since the last glacial or may have predated the last glacial. The constancy or expansion of population sizes on the Japanese islands, and in contrast a bottleneck in population size on the Korean island Jeju, suggests that these islands may have provided different conditions for sustaining populations. The result of palaeodistribution modeling indicates that the longitudinal range of the species as a whole has not changed greatly since the last glacial maximum. These results indicate that exposed seafloors during the glacial period formed both effective and ineffective migration corridors. These findings may shed light on the effects of seafloor exposure on the migration of plants distributed across continental islands.

The architecture of trees is a crucial determinant of their performance through light capture and mechanical stability. Comparison of architectural traits between closely related dioecious species is predicted to reveal both inter-specific and sexual differences. The former may reflect life-history characteristics such as microhabitat preferences, and the latter may reflect costs of reproductive allocation. We measured branching structure, leaf traits, wood density, and biomass of each vegetative component in the dioecious shrubs Lindera praecox and Lindera triloba to explore architectural differences according to species and gender. L. triloba was less branched but had a greater total leaf mass per shoot having larger and heavier leaves than L. praecox; most of these traits did not differ by gender. Allometric relationships between height and branch biomass corroborated our results of branching structure. The allometric relationships between tree size and leaf biomass demonstrated that in larger size classes females of both species had greater leaf biomass than males. Females of both species also showed lower tree height than males. This study suggests that tree architecture is influenced by both life-history strategy and resource-allocation pattern. Branching structure and branch biomass showed inter-specific differences, with the highly branched L. praecox apparently more shade tolerant than L. triloba; its tolerance is likely adaptive in its preferred microhabitat where is often lit poorly. Sexual differences in leaf biomass and tree height growth may reflect higher reproductive costs incurred by females.

Genetic diversity is essential for species to sustain their populations and evolutionary potential. In order to develop effective conservation strategies for rare species, it is necessary to understand differences in patterns of genetic diversity between common and rare species. Data about population genetic structure is important to design effective conservation strategies for rare species. In this study, we compared the genetic diversity and population genetic structure of a common species, Rhododendron weyrichii, to those of two rare species, Rhododendron sanctum and Rhododendron amagianum, with different geographic distributions. We analyzed five microsatellite loci in 16 populations of R. weyrichii, 9 populations of R. sanctum, and 6 populations of R. amagianum. As expected, the level of genetic diversity indicated by allelic richness and gene diversity was lower for the rare species R. sanctum than for the common species R. weyrichii. However, there was no statistically significant difference in genetic diversity between R. weyrichii and the other rare species, R. amagianum. Analyses of the isolation-by-distance pattern, neighbor-joining trees, and Bayesian clustering indicated that R. sanctum had a strong population genetic structure whereas R. amagianum exhibited very weak genetic structure among populations and that there was moderate population genetic structure for R. weyrichii. Therefore, the degree and pattern of population genetic structure in each species was unrelated to its rarity and instead merely reflected its geographic distribution.

BACKGROUND AND AIMS: It is important to consider the modular level when verifying sexual dimorphism in dioecious plants. Nevertheless, between-sex differences in resource translocation among modules (i.e. physiological integration) have not been tested at the whole-plant level. In this study, sexual differences in physiological integration were examined among ramets, within a genet in the dioecious sprouting shrub Lindera triloba, by a field experiment with girdling manipulation. METHODS: Female and male genets were randomly assigned to girdled or intact groups. Girdling of the main ramets was conducted in May 2009 by removing a ring of bark and cambium approx. 1 cm wide at a height of 80-100 cm. The effects of treatment and sex on ramet dynamics (mortality, recruitment and diameter growth) and inflorescence production during 1 year after girdling were examined. KEY RESULTS: The diameter growth rate of main ramets of both sexes was lower at ground level (D(0)) but higher at breast height (dbh) in girdled than in intact groups. In sprouted ramets with a dbh of 0-2 cm, males in girdled groups had lower growth rates at D(0) than those of intact groups, whereas no girdling effect was found for females. The main ramets in girdled groups produced more inflorescences than intact groups, irrespective of sex, but male ramets showed a greater response to the treatment than females. CONCLUSIONS: In L. triloba, physiological integration exists at the whole-plant level, and sprouted ramets are dependent on assimilates translocated from main ramets, but this dependence weakens as sprouted ramets get larger. Female sprouted ramets can grow in a physiologically independent manner from the main ramet earlier than those of males. This study highlights the importance of considering modular structures and physiological integration when evaluating sexual differences in demographic patterns of clonal plants.