渡辺 洋一

Abstract Unraveling species boundaries is pivotal for evolutionary biology and conservation endeavors. However, it proves challenging in instances where recent speciation is intertwined with complex demographic histories and natural selection processes. The Rhododendron keiskei complex, an evergreen rhododendron distributed in East Asia, consists of a widespread variety (R. keiskei var. keiskei) and a more restricted R. keiskei var. hypoglaucum. Intriguingly, the latter is exceptionally rare yet displays a disjunction that spans approximately 1100 km. This study aimed to elucidate the evolutionary backgrounds of the enigmatic disjunctions of R. keiskei var. hypoglaucum and to propose species delimitation within the species complex. An integrative approach, combining genomic data (MIG‐seq and GBS‐derived SNPs) with Scanning Electron Microscopy analysis of leaf microstructures was adopted in this study. Phylogenetic analyses revealed significant divergence among the studied rhododendrons. Genetic demographic analyses favored the population models that assumed non‐monophyly of two disjunct populations of R. keiskei var. hypoglaucum indicating their independent origins. Recent gene flow between the widespread R. keiskei var. keiskei and “var. hypoglaucum” populations were limited due to geographic and habitat isolation factors, even in areas where their distributions overlap. Detailed morphological assessments detected distinctions between morphologically similar “var. hypoglaucum” populations based on leaf microstructures and flowering habits. Our study has shown that the apparent disjunctions of rare rhododendrons are more likely attributed to morphological convergence, possibly due to similar environmental selections in unrelated taxa. The finding highlights the importance of an integrative approach for resolving taxonomic challenges in plant species complexes.

<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>

Hypecoum erectum L., a widespread species in northern Eurasia, is a valuable medicinal plant, but its chloroplast genome has not previously been reported. We determined its complete chloroplast genome using a high-throughput sequencing technique. Its total length was 169,241 bp, consisting of a large single-copy region of 93,301 bp and a small single-copy region of 17,316 bp, separated by a pair of inverted repeat regions of 29,312 bp. A total of 140 genes were annotated, including 91 protein coding genes, 41 tRNA genes, and eight rRNA genes. The phylogenetic analysis shows that H. erectum and H. zhukanum of the subfamily Hypecoideae are monophyletic with the highest support.

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.