华木莲居群遗传结构与保护单元

华木莲(Sinomanglietia glauca)仅分布于江西宜春和湖南永顺, 是我国一级重点保护植物。前人采用RAPD、ISSR以及叶绿体SSCP(single-stranded conformation polymorphism)标记对华木莲进行了居群遗传学研究, 但未包括后发现的湖南居群或未检出居群内遗传变异。为了全面检测华木莲遗传多样性及其空间分布格局, 并据此确定保护单元, 本研究采用细胞核微卫星标记对华木莲所有4个居群共77个个体进行了居群遗传学分析。结果表明, 华木莲具有较低的遗传多样性(平均等位基因数A = 2.604, 平均期望杂合度H_E = 0.423)和较高的遗传分化(F_ST = 0.425)。STRUCTURE和主成分分析(Principal Coordinated Analysis, PCA)将4个居群首先分为江西、湖南两组, 江西的2个居群实际上是同一个自然繁育居群, 而湖南的2个居群则为2个分化明显的自然繁育居群。研究还发现湖南居群存在明显的杂合子过剩现象, 可能是小居群内随机因素造成的。研究结果表明华木莲可能在近期历史上遭受过强烈的瓶颈效应, 导致种群缩小、遗传多样性丧失和居群分化加剧, 需要加强对其进化潜力的保护。在制定保护措施时, 需要考虑其较高的遗传分化水平, 根据遗传结构可以将其划分为3个保护单元, 即湖南居群和江西居群分别为2个进化显著单元, 湖南居群进一步划分为2个管理单元(分别为朗溪乡云盘村和小溪乡鲁家村居群)。

Population genetic structure and conservation units of Sinomanglietia glauca (Magnoliaceae)

Sinomanglietia glauca, a species endemic to Yichun in Jiangxi Province and Yongshun of Hunan Province in Central China, was listed as Category I of the National Key Protected Wild Plants in 1999 (as a synonym of Manglietia decidua). Several studies on the population genetics of this endangered species have been reported. However, these studies either excluded Hunan populations or failed to detect any variation within populations. In this study, all four known populations of S. glauca found were used to investigate genetic diversity and genetic structure using nuclear microsatellite markers. Our results showed that S. glauca had relatively low genetic diversity (A = 2.604, H_E = 0.423) and significant population differentiation (F_ST = 0.425). Assignments analysis by STRUCTURE and Principal Coordinated Analysis indicated that Jiangxi and Hunan populations formed two independent groups. Only one natural breeding population was identified in Jiangxi whereas two were revealed in Hunan. We found a striking heterozygosity excess in the Hunan populations, a phenomenon that might be caused by allelic frequencies differing between male and female parents by chance alone within small population. The results of this study suggest that S. glauca could have experienced recent historic bottleneck(s) which resulted in reduction of population size, loss of genetic diversity and strong population differentiation. The distribution pattern of genetic diversity clearly indicates that S. glauca should be treated as three conservation units, i.e., two evolutionarily units (Jiangxi unit and Hunan unit), and Hunan ESU subdivided into two management units (YPC and LJC).