Genetic differentiation and evolution of broad-leaved evergreen shrub and tree varieties of Daphniphyllum macropodum (Daphniphyllaceae)

<p><span>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. <em>Daphniphyllum macropodum</em> 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 of Japan. Chloroplast DNA variations and genome-wide single nucleotide polymorphisms across <em>D. macropodum</em> populations and <em>D. teijsmannii</em> as an outgroup were used to reveal 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, which 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, 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.</span></p>