南亚热带森林片断化对厚壳桂种群遗传结构的影响

Genetic structure of Cryptocarya chinensis in fragmented lower subtropical forests in China based on ISSR markers

森林片断化是造成全球生物多样性丧失的主要原因,但从种群遗传学角度开展的研究还远远不够。因此,本文采用ISSR(inter-simplesequencerepeat)方法对广东省鼎湖山、黑石顶、大雾岭、古田、萝岗和饶平6个地点的南亚热带片断化森林中的厚壳桂(Cryptocaryachinensis)种群的遗传多样性进行了研究。每个种群分成体、小树和幼苗3个年龄级采样,共采集厚壳桂样品448个。7个ISSR引物共扩增出209条多态性带。研究结果表明,6个厚壳桂种群的总遗传多样性为0.1529,种群平均遗传多样性为0.0537。和保护较好的厚壳桂种群相比,萝岗和饶平的两个村边林种群的遗传多样性较低。6个厚壳桂种群间的遗传分化系数(GST)为0.6489。AMOVA分析结果表明,总的遗传变异中,67.97%(P<0.0002)的遗传变异存在于种群间,2.06%(P<0.01)的遗传变异存在于不同年龄级之间,29.96%(P<0.0002)的遗传变异存在于种群内。基于遗传距离的UPGMA分析结果表明,6个厚壳桂种群大致分成两支:一支包括大雾岭和黑石顶2个种群,另一支包括其他4个种群。鼎湖山、古田、大雾岭和黑石顶不同年龄级均各自聚合在一起。可以看出,森林的破碎化导致了南亚热带厚壳桂种群遗传多样性降低,种群间基因流受阻,提示我们对于同一地区的易危物种,这种威胁将很大,急需开展相关的保护研究。

Forest fragmentation is the main threat to global biodiversity. However, genetic information conceming the effects of fragmentation is currently lacking for plant species in lower subtropical China. To enrich scientific understanding of this issue, we employed the ISSR （inter-simple sequence repeat） markers to determine the genetic structure in Cryptocarya chinensis. Four hundred and forty-eight individuals from six fragmented populations in Guangdong Province were sampled according to age classes. Four of these populations, DHS, HSD, DWL and GT, were in nature reserves, and the other two, LG and RP, were near villages. Seven ISSR primers produced a total of 209 polymorphic bands which were used to evaluate genetic variation. The results showed that C. chinensis displayed unexpectedly low genetic variation within populations （Hp =0.0537） and high genetic differentiation among populations （GST=0.6489, φST=0.6797）. Genetic variations in LG （0.0251） and RP （0.0000） populations were lower than in the other four well-conserved populations. Considering age classes, low but significant genetic differentiation characterized DHS and HSD populations. These results indicate that C. chinensis has experienced a recent decrease in population size which may cause a bottleneck effect. The resulting fragmentation increased genetic drift and inbreeding, causing theloss of genetic variation. Our results for C. chinensis may be general for other species in this area and therefore more work related to conservation is urgently needed.