天然片断生境中山姜(Alpinia japonica)种群遗传结构

Genetic structure of Alpinia japonica populations in naturally fragmented habitats

理论和实验研究表明片断化是导致生物多样性丧失的主要因素之一，但有关研究基本上集中在人类活动引发的片断化生境体系中。由于长期气候变化以及地形等因素的影响，一些物种的种群之间天然情况下就存在隔离，对这些种群进行研究可以弥补人类活动引起的片断化体系经历时间较短的不足。山姜是一个喜湿耐荫的多年生植物，分布在热带亚热带地区，由于气候和地形原因，该物种在浙江东部呈现天然片断化状态，如在浙江天童森林公园及其周边地区，仅分布在少数几个沟谷中。以这些种群为对象，采用RAPD标记分析经历长期天然片断化山姜种群遗传多样性程度和遗传分化格局。7条RAPD引物获得了69个位点，其中多态位点68个。种群水平遗传多样性较高，多态位点百分比、期望杂合度和Shannon多样性指数分别为78.81％-85.51％、0.3170-0.3430、0.4560-0.4914，这与其异交的繁殖方式有关，同时与山姜克隆生长，每个世代维持的时间长，种群更新降低也有关系。遗传变异大多分配在种群内，但种群问遗传分化达到显著程度，φST为0.297，计算的基因流中等，为0.592，不足以克服长期遗传漂变导致的种群分化，Mantel检验表明遗传距离与空间距离不存在相关关系，显示了长期片断化状态下遗传漂变的作用。

Fragmentation is the process that a large continuous habitat is destructed into a couple of small, spatially isolated habitats. Theoretical and empirical studies have shown that habitat fragmentation is one of the most important threats leading to biodiversity loss. Isolated populations are prone to loss of genetic diversity and to local extinction, through genetic drift, inbreeding and decrease in rescue effect led by reduced gene flow. However, till now most studies concerning the genetic consequences of habitat fragmentation involve fragmentation systems caused by human disturbance. Long-term climatic changes or topography may also lead to habitat fragmentation and result in distinct isolation among populations. Such naturally fragmentation systems have experienced long-term fragmentation, avoiding short history in anthropogenic fragmentation systems. However, genetic structure populations of natural fragmentation has not been well checked. Alpinia japonica （Thunb.） Miq. （Zingiberaceae） is a perennial clonal species of tropical and subtropical areas. It is hermaphroditic, but it has two floral phenotypes and has a mechanism to decrease probability of pollination of the same floral phenotype. This species grows in wet and close forest habitats. In the subtropical area of eastern China, for example in eastern Zhejiang Province, the habitats are naturally patchy and restricted. We studied the genetic structure of naturally fragmented populations in Tiantong Forest Parks using RAPD markers. Seven primers revealed 69 bands, among them 68 were polymorphic. High genetic diversity was found within populations. The percentage of polymorphic loci, expected heterozygosity and Shannon information index were 78. 81%-85.51% , 0.3170-0.3430, 0.4560-0.4914, respectively. Relatively high genetic diversity in A. japonica is coincided with its life history characteristics, i. e. , outcrossing, long-lived perennial. Within population genetic variation is slightly higher than those of species of Zingiberaceae and means of outcrossers or long-lived perennial, indicating that genetic diversity has not apparently affected by fragmentation. This situation is due to the strong clonality, which prolongs the parental generation and reduces the turnover of generation. However, there is a signal of the consequences of long-term fragmentation on genetic differentiation. Although fine scale in the present study, moderate and significant differentiation has been found among populations （φST= 0.297, p 〈0.01 ）. The differentiation is much higher than those with similar spatial scale. Furthermore, no isolation-by- distance pattern was found using Mantel test, indicating that genetic drift had overcome the impact of gene flow （0.592）.