2.4 | Climatic conditions and leaf characters
To evaluate climatic conditions that populations experienced, we obtained climatic value mesh data (Japan_Meteolorogical_Agency 1987) at the third meshes (about 1 km squares) of Japan Standardized Regional Mesh Codes (JIS X0410), where the 24 populations were located. Although the data have been updated (the latest version in 2020), we used the old version (1953–1983), because we evaluated climatic conditions before recent climate changes. From the data, we used the mean of daily-mean temperature (˚C) in each month, the precipitation (mm) in each month, the maximum snow depth (cm) in each month from December to March (28 variables in total).
For the 155 leaves in the 12 populations, we obtained seven (a–g) measurements (mm) of leaf characters described in Noshiro (1984): a) blade length, b) blade width, c) inter-sinus blade width, d) distance to the widest point from base, e) length of the longest lateral vein, and f) intra-tooth vein length and g) tooth breadth at the end of the longest lateral vein.
To evaluate variations in climatic conditions among populations and in leaf characters among leaves, we conducted PCA using prcomp function in R 4.2.2. We obtained the contributions of the first to fifth PCs to total variation and the loadings of 28 variables in climatic conditions and seven variables in leaf characters to the first and second PCs. We plotted the coordinates of the first and second PC values of each population and these values of each leaf. To describe variation in leaf characters among populations, we calculated the median of PC values of leaves in each population and plotted these PC coordinates.