金钱槭和云南金钱槭遗传多样性比较研究

金钱槭属(Dipteronia)是我国特有少种属,属下仅金钱槭(D. sinensis)和云南金钱槭(D. dyeriana)两种。该文用RAPD标记揭示了金钱槭的遗传多样性和遗传结构,并与云南金钱槭的RAPD研究结果进行了比较。同时,对两物种遗传距离与地理距离的相关性进行了分析,结果有助于阐释该属植物遗传变异的产生机制。研究显示,18条随机引物在17个金钱槭居群(226个个体)中检测到128个扩增位点,物种水平的多态位点比率为92.97%,在4个云南金钱槭居群(45个个体)中则检测到103个扩增位点,物种水平的多态位点比率为81.55%,金钱槭的多态位点比率高于云南金钱槭。相似性系数值、Shannon多样性指数和Nei基因多样性指数分析反映了与多态位点比率相一致的结果。AMOVA(Analysis of molecular variance)分析结果显示,金钱槭居群内、居群间的遗传变异分别占总变异量的56.89%和43.11%。云南金钱槭居群内、居群间的遗传变异分别占总变异量的57.86 %和42.14%。Shannon多样性指数、Nei基因多样性指数的分析结果与AMOVA分析结果趋势相同。上述特征值揭示,金钱槭和云南金钱槭居群间的遗传分化均已达到较高水平,推测居群间低水平的基因流可能是导致上述现象产生的原因之一。遗传距离与地理距离的相关分析结果显示,金钱槭居群间的遗传距离与经度差异存在极显著水平的相关性(p<0.01),云南金钱槭居群间的遗传距离与地理隔离则无显著相关关系。说明在大尺度上遗传距离与地理距离相关而在小范围内则无上述关系,该结果可能与位于不同分布区内的物种所承受的生境选择压力不同有关。建议在对该属植物进行就地保护时,应设立多个保护点,保护自然居群及其周围生境;在迁地保护时,应通过加大居群间种子和幼苗的交换,人为创造基因交流和重组的条件,保存该属植物的遗传多样性。

A COMPARATIVE STUDY ON THE GENETIC DIVERSITY OF DIPTERONIA SINENSIS AND DIPTERONIA DYERIANA

Dipteronia is an endemic genus to China and includes only two species, Dipteronia sinensis and D. dyeriana. Based on RAPD markers, a comparative study on the genetic diversity and genetic structure of Dipteronia was performed. In total, 128 and 103 loci were detected in 17 D. sinensis populations and 4 D. dyeriana populations, respectively, using 18 random primers. These results showed that the proportion of polymorphic loci for the two species were 92.97% and 81.55%, respectively, indicating that the genetic diversity of D. sinensis was higher than that of D. dyeriana. Analyses based on similarity coefficients, Shannon diversity index and Nei gene diversity index, also confirmed this result. AMOVA analysis demonstrated that the genetic variation of D. sinensis within and among populations accounted for 56.89% and 43.11% of the total variation, respectively, and 57.86% and 42.14%, respectively, of D. dyeriana. The Shannon diversity index and Nei gene diversity index showed similar results. The above-mentioned characteristics indicated that the genetic diversity levels of these two species were extremely similar and that the interpopulational genetic differentiation within both species was relatively high. Analysis of the genetic distance among populations also supported this conclusion. Low levels of interpopulational gene flow within both species were believed to be among the leading causes for the above-mentioned phenomenon. The correlation analysis between genetic and geographical distances showed that there existed a remarkably significant correlation between the genetic distance and the longitude difference among populations of D. sinensis (p<0.01) while no significant correlation existed between genetic and geographical distances among populations of D. dyeriana. This indicates that genetic distance was correlated with geographical distances at large scales other than at small scales. This result may be related to differences in selection pressure exerted on species by their habitats with different distribution ranges. We suggest that in situ conservation efforts should focus on establishing more sites to protect the natural populations and their habitats. Ex situ conservation efforts should focus on enhancing the exchange of seeds and seedlings among populations to facilitate gene exchange and recombination to help conserve genetic diversity.