用分子标记揭示植物随机大居群中亚居群的遗传结构——茅栗自然居群空间遗传结构的SSR分析

SUBPOPULATION GENETIC STRUCTURE IN A PANMICTIC POPULATION AS REVEALED BY MOLECULAR MARKERS: A CASE STUDY OF CASTANEA SEQUINII USING SSR MARKERS

采用微卫星标记对茅栗(Castanea sequinii)随机大居群以及其中各亚居群的遗传结构进行了空间自相关分析,以探讨植物自然居群内遗传变异的分布特征及其形成机制。通过9对微卫星引物所产生的119个多态位点,测定了大别山区域内茅栗居群以及各亚居群的空间自相关系数Moran’sI值。结果表明大别山分布的野生茅栗为一个缺乏空间结构的随机大居群,茅栗亚居群之间频繁的花粉流削弱了地理隔离导致的遗传漂变或分化作用在维系居群随机遗传结构中具有的重要作用。但是,在接近亚居群大小的地域范围内(0.228km)具有一定的空间结构,即小地域尺度中的亚居群存在着空间遗传结构。取样的3个亚居群在小格局范围内都存在一定的空间结构,遗传变异基本上呈非随机分布,在短距离内(61m)3个亚居群一致表现出不同程度的显著正相关,而随着距离的增加,Moran’sI值虽然在不同亚居群间存在一定差异变化,但是总体而言趋向预期值,即不存在空间结构,说明其遗传变异在亚居群内只是在短距离内形成一定的空间结构。研究认为有限的种子散播以及微生境选择等因素可能是产生这种小格局的遗传结构的主要原因。上述研究结果有助于进一步了解植物随机大居群的进化历史和生态过程,同时也为栗属植物中国特有种的保育策略提供了科学依据。

Castanea squinii, an endemic tree widely distributed in China, has great value both for chestnut breeding and in natural forest ecosystems. The spatial genetic structure within and among populations is an important part of the evolutionary and ecological genetic dynamics of natural populations and can provide insights into effective conservation of genetic resources. In the present study, the spatial genetic structure of a natural population of C. sequinii in the Dabie Mountain region, including three subpopulations, was investigated using SSR markers. Nine prescreened SSR loci generated 29 - 33 alleles and were used for spatial autocorrelation analysis. Based on Moran＇ s I coefficient, a panmictic population of C. sequinii was revealed that lacked spatial genetic structure in the Dabie Mountain region. These results suggested that high pollen flow among subpopulations counteracted genetic drift or genetic differentiation and played an important role in maintaining a random and panmictic population structure in the region. However, spatial genetic structure was detected in the geographic range of each subpopulation＇ s scale （0.228 km） indicating that spatial genetic structure occurred at a fine scale within each subpopulation. All three subpopulations showed significant fine-scale structure. The genetic variation was not randomly distributed within 61 m in each subpopulation （Moran＇s I positive values）. However, although Moran＇s I values varied among the different subpopulations, Moran＇s I in all the three subpopulations reached the expected values with an increase in distance suggesting a general patchy distribution in the subpopulations. The fine-scale structure seemed to be influenced by restricted seed dispersal and microenvironment selection. These results have important implications for understanding the evolutionary history and ecological process of natural populations of C. squinii and provide baseline data for formulating conservation strategies of Castanea species.