Gifu Academy of Forest Science and Culture, 88 Sodai, Mino, Gifu, 501-3714, Japan.
Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan.
J Plant Res. 2019 Nov;132(6):741-758. doi: 10.1007/s10265-019-01134-6. Epub 2019 Sep 5.
Species delimitations by morphological and by genetic markers are not always congruent. Magnolia kobus consists of two morphologically different varieties, kobus and borealis. The latter variety is characterized by larger leaves than the former. For the conservation of M. kobus genetic resources in natural forests, the relationships between morphological and genetic variation should be clarified. We investigated variations in nuclear microsatellites, chloroplast DNA (cpDNA) sequences and leaf morphological traits in 23 populations of M. kobus over the range of species. Two genetically divergent lineages, northern and southern were detected and their geographical boundary was estimated to be at 39°N. The northern lineage consisted of two genetic clusters and a single cpDNA haplotype, while the southern one had multiple genetic clusters and cpDNA haplotypes. The northern lineage showed significantly lower genetic diversity than the southern. Approximate Bayesian computation indicated that the northern and southern lineages had experienced, respectively, population expansion and long-term stable population size. The divergence time between the two lineages was estimated to be 565,000 years ago and no signature of migration between the two lineages after divergence was detected. Ecological niche modeling showed that the potential distribution area in northern Japan at the last glacial maximum was very small. It is thus considered that the two lineages have experienced different population histories over several glacial-inter-glacial cycles. Individuals of populations in the central to northern part of Honshu on the Sea of Japan side and in Hokkaido had large leaf width and area. These leaf characteristics corresponded with those of variety borealis. However, the delimitation of the northern and southern lineages detected by genetic markers (39°N) was not congruent with that detected by leaf morphologies (36°N). It is therefore suggested that variety borealis is not supported genetically and the northern and southern lineages should be considered separately when identifying conservation units based not on morphology but on genetic markers.
形态和遗传标记的物种界定并不总是一致的。红花玉兰由两个形态上不同的变种组成，即红花玉兰和白玉兰。后者的叶子比前者大。为了保护红花玉兰在自然森林中的遗传资源，应该明确形态和遗传变异之间的关系。我们调查了 23 个红花玉兰种群的核微卫星、叶绿体 DNA（cpDNA）序列和叶片形态特征的变异，这些种群分布在物种范围内。检测到两个遗传上分化的谱系，北方和南方，其地理边界估计在 39°N。北方谱系由两个遗传群和一个单一的 cpDNA 单倍型组成，而南方谱系有多个遗传群和 cpDNA 单倍型。北方谱系的遗传多样性明显低于南方。近似贝叶斯计算表明，北方和南方谱系分别经历了种群扩张和长期稳定的种群大小。两个谱系之间的分化时间估计为 565000 年前，在分化后没有检测到两个谱系之间的迁移迹象。生态位模型表明，末次冰期最大时日本北部的潜在分布区非常小。因此，可以认为这两个谱系在几个冰期-间冰期循环中经历了不同的种群历史。日本海一侧本州中部至北部和北海道的种群个体具有较大的叶片宽度和面积。这些叶片特征与白玉兰变种相对应。然而，遗传标记（39°N）检测到的北方和南方谱系的划分与叶片形态（36°N）检测到的划分不一致。因此，建议从遗传上不支持白玉兰变种，在基于遗传标记而不是形态学来确定保护单位时，应分别考虑北方和南方谱系。
