Fig 1.
The distribution of the study populations of Betula ermanii.
The location of the study populations (a) and their vertical distribution (b). Black circles indicate tetraploid populations; white circles indicate diploid populations; gray shading indicates habitat suitable for B. ermanii as predicted by niche modeling [26]. The 14 populations were: URU, Uryu; AKS, Akkeshi; HKD, Hakkoda; GYS, Goyo-san; CKS, Choukai-san; BDS, Bandai-san; MKT, Mikuni-touge; YGT, Yatsu-gatake; APW, Alps-west; NGH, Nougouhaku-san; APS, Alps-south; SHK, Shaka-gatake; TRG, Tsurugi-san; ISZ, Ishizuchi-san. The shapefiles of land boundary were made using file from Natural Earth (https://www.naturalearthdata.com/). The base map was made using files from The Geospatial Information Authority of Japan (https://www.gsi.go.jp/kiban/index.html).
Fig 2.
Images of Betula ermanii in the southern boundary populations.
Betula ermanii habits in (a) Ishizuchi-san (ISZ) and (b) Tsurugi-san (TRG) on Shikoku Island and (c) Shaka-gatake (SHK) on the Kii Peninsula. These images were taken by the author T. A.
Table 1.
The location of the Betula ermanii populations and their estimated ploidy level.
Table 2.
The number of trees per Betula ermanii population used for the morphometric analyses, and their trait values.
Fig 3.
Examples of leaf and seed images of Betula ermanii and the morphological measurements taken.
(a) Leaf length (mm); (b) Leaf width (mm); (c) Length of leaf base (mm); (d) Seed length (mm); (e) Seed width (mm); (f) Length of seed wing (mm). The leaf and seed images were taken by the author T. A.
Fig 4.
A principal component analysis (PCA) of Betula ermanii leaf morphological traits.
Black circles indicate individuals from tetraploid populations; white circles indicate individuals from diploid populations; black-filled double circles indicate tetraploid individuals from TRG and ISZ populations. Each circle is based on the principal component score. Red letters and arrows indicate the principal component loadings for each variable (axes 1 and 2), calculated from the rotation and standard deviation of each variable. The images of leaves are typical silhouettes of relevant samples along each axis. LeafA, leaf area (cm2); LeafL, leaf length (mm); LeafW, leaf width (mm); LeafL/LeafW, leaf length/leaf width; Perimeter, perimeter of leaf (mm); Perimeter/LeafA, perimeter of leaf/leaf area; Vein, the number of leaf veins; BaseL, length of leaf base (mm); BaseL/LeafL, length of leaf base/leaf length. The leaf images were taken by the author T. A.
Fig 5.
Boxplots of leaf area, leaf length/leaf width, perimeter of leaf/leaf area, the number of leaf veins, length of leaf base/leaf length, weight of 100 seeds, area of 100 seeds, seed length/seed width, and length of seed wing/seed width.
Green plots indicate the traits of diploid populations; gray plots indicate the traits of tetraploid populations; white circles indicate the traits of tetraploid individuals from TRG and ISZ populations. For site abbreviations, see Fig 1; higher latitudinal populations are shown on the right-hand side, and lower latitudinal populations on the left. Different letters at the top of each box indicate statistically significant differences between populations based on a Tukey multiple comparison performed for each experimental year, based on a 95% confidence level.
Fig 6.
A principal component analysis (PCA) of Betula ermanii seed morphological traits.
Black circles indicate individuals from tetraploid populations; white circles indicate individuals from diploid populations; black-filled double circles indicate tetraploid individuals from the ISZ population. Each circle is based on the principal component score. Red letters and arrows indicate the principal component loadings for each variable (axes 1 and 2), calculated from the rotation and standard deviation of each variable. The images of seeds are typical silhouettes of samples close to the values along each axis. SeedA, area of 100 seeds (cm2); Weight, weight of 100 seeds (mg); SeedL, seed length (mm); SeedW, seed width (mm); SeedL/SeedW, seed length/seed width; WingL, length of seed wing (mm); WingL/SeedW, length of seed wing/seed length. The seed images were taken by the author T. A.