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.