伯乐树种群遗传多样性及遗传结构

Genetic diversity and population structure of Bretschneidera sinensis,an endangered species

了解种内遗传变异信息是制定种群遗传多样性保护策略的前提。伯乐树(Bretschneidera sinensis)是古老的单科属孑遗植物,被列为国家一级保护植物。为了揭示伯乐树天然种群的遗传多样性和遗传结构,采用7条ISSR引物分析了采自湖南、江西、广东、广西和贵州5个省区15个天然种群的219株个体的样本。结果显示,伯乐树遗传多样性水平较高,物种和种群水平上的多态位点百分率(PPB)分别为74.42%和38.06%,Shannon’s表型多样性指数(I)分别为0.3630和0.2081,Nei’s基因多样性指数(He)分别为0.2397和0.1405。种群间遗传分化显著,基于表型多样性指数和分子方差分析揭示的伯乐树天然种群间遗传分化系数分别为FST=0.4267、GST=0.2973。UPGMA聚类表明,参试的15个天然种群可分为2大组群;Mantel检测发现,种群间遗传距离与其地理距离存在显著相关性(r=0.3096,P=0.008)。基于上述研究结果,我们认为,伯乐树濒危原因不是种群遗传进化潜力小,而是由于生境破坏严重,以及自身繁殖能力低、适应性差、竞争力弱等生物学特征导致的。建议优先保护遗传多样性较为丰富的阳明山、莽山、乳阳、八面山种群,并对种群近交衰退开展相应的监测工作。

Amounts and distribution of intraspecific genetic variation provide benchmarks for developing conservation strategies. Bretschneidera sinensis is a monotypic relic species listed in the First Grade of the List of Wild Plants Under State Protection （First Batch） in China. We examined the genetic diversity and ge- netic structure of 219 B. sinensis individuals sampled from 15 natural populations distributed in Hunan, Ji- angxi, Guangdong, Guangxi, and Guizhou using inter-simple sequence repeat （ISSR） markers generated by seven ISSR primers. The percentage of polymorphic bands （PPB） at the species and population level was 74.42% and 38.06%, respectively. Shannon＇s index （/） of phenotypic diversity at the species and population level was 0.3630 and 0.2081, respectively, and Nei＇s genetic diversity （He） at the species and population level was 0.2397 and 0.1405, respectively. These results indicate that B. sinensis contains relatively high levels of genetic diversity. Analysis of molecular variance （AMOVA） and estimates of the coefficient of genetic differentiation based on phenotypic diversity index also indicated high levels of population subdivision （Gsz = 0.2973; Fsx= 0.4267） in the species. Analysis of the ISSR data using UPGMA further revealed that popula- tions were genetically clustered into two groups, while a Mantel test showed that genetic divergence was sig- nificantly correlated with geographical distance among populations （Mantel test; r = 0.3096, P = 0.008）. We conclude from our results that B. sinensis is not endangered due to low evolutionary potential stemming from low genetic diversity, but by habitat destruction coupled with a low reproductive capacity, poor adaptability and weak competitiveness. The Mt. Yangming, Mt. Mangshan, Ruyang, and Mr. Bamianshan populations of the species with higher genetic diversity should be given priority for conservation, and inbreeding depression monitoring should be conducted.