基于28S, COI和Cytb基因序列的薜荔和爱玉子传粉小蜂分子遗传关系研究

The molecular genetic relationship between the pollinators of Ficus pumila var.pumila and Ficus pumila var. awkeotsang

薜荔和爱玉子均属于桑科榕属植物,二者为同一物种的原变种与变种的关系,早期研究认为这两种榕树与同一种传粉榕小蜂(Wiebesia pumilae(Hill))建立了稳定的互利共生关系,但近期在形态学、生态学、传粉生物学等方面对二者的研究结果表明,薜荔传粉小蜂和爱玉子传粉小蜂之间可能发生了遗传分化。实验用核糖体28SrDNAD1-D3区、线粒体Cytb及COI基因部分序列,对采自福建3个不同样地的薜荔传粉小蜂和3个不同品系的栽培爱玉子的传粉小蜂进行分析,结果表明:(1)薜荔传粉小蜂和爱玉子传粉小蜂的核糖体28S序列的碱基组成中A,T,G,C 4种含量较平均,C+G的平均含量(56%)稍高于A+T的含量(44%)。线粒体Cytb序列中A+T的含量(76.1%)明显高于C+G的含量(23.9%),COI序列中A+T的含量(71.9%)也明显高于G+C的含量(28.1%),这是膜翅目昆虫线粒体基因的普遍特征。在薜荔和爱玉子传粉小蜂的线粒体Cytb及COI基因中,密码子第三位点A+T的含量最高。(2)比较薜荔和爱玉子传粉小蜂的3种分子标记的变异范围显示,28S进化速度较Cytb及COI序列慢,比较保守,更适合科、亚科等较高分类单元的研究。薜荔传粉小蜂与爱玉子传粉小蜂之间的亲缘关系较近,采用Cytb与COI序列进行分析更为精确。(3)用Cytb及COI序列对薜荔传粉小蜂与爱玉子传粉小蜂之间的遗传距离进行分析显示,薜荔传粉榕小蜂个体间Cytb序列平均遗传距离为0.0054,爱玉子传粉小蜂个体间的Cytb遗传距离为0.0164;薜荔传粉小蜂与爱玉子传粉小蜂群体之间的Cytb序列平均遗传距离为0.1385;COI序列的薜荔传粉榕小蜂个体间遗传距离为0.0048,爱玉子传粉小蜂各样本间平均遗传距离为0.0102;薜荔传粉小蜂与爱玉子传粉小蜂群体间COI序列平均遗传距离为0.1896,两群体间的遗传距离(差异大于10%以上)明显大于群体内各样本之间的遗传距离,表明薜荔传粉小蜂与爱玉子传粉小蜂之间已经发生了很大的遗传分化,其变异水平达到了种间分化水平,即薜荔传粉小蜂与爱玉子传粉小蜂为两个不同的种。

Ficus pumila var. pumila and Ficus pumila var. awkeotsang are two varieties of the same species （Moraceae）; one is the original variant while the other is a later variant and, they have long been considered to interact with the same species of pollinator. However, the recent studies in morphology, ecology and pollination biology suggest that a differentiation between the pollinators of Ficus pumila var. pumila and Ficus pumila var. awkeotsang wasps may have occurred during the evolution. In the present studies, we used three molecular markers including 28SrDNA D1-D3, the mitochondrial Cytb and COI genes to investigate the genetic relationship of these two pollinators. The pollinator samples were collected from Ficus pumila var. pumila at three different locations as well as three cultivars of Ficus pumila var. awkeotsang. The data are summarized as follows： （1） The distribution of the four bases including A, T, G, C in the 28SrDNA sequence from the pollinators of Ficus pumila var. pumila and Ficus pumila var. awkeotsang is relatively akin. The average content of C ＋ G （56%） is slightly higher than the average content of A＋T （44%）. The average content of A＋T in the mitochondrial Cytb sequence is 76.1%, significantly higher than the average content of C＋G （23.9%）. The COI sequence analysis shows a similar result, with the A＋T content （71.9%）, higher than the G＋C content （28.1%）. This base composition pattern is consistent cross along hymenopteran mitochondrial sequences. Furthermore, in the Cytb and COI sequences, it appears to have the highest content of A/T base at the third position of a codon. （2） The 28SrDNA sequence evolution appears to be slower than the Cytb and COI gene sequences, is relatively conservative, and maybe more suitable for senior-order （family or subfamily） phylogenetic studies. In contrast, the Cytb and COI molecular markers may be more suitable for the genetic relationship analyses between the pollinators of Ficus pumila var. pumila and Ficus pumila var. awkeotsang due to their close ties. （3） The results derived from genetic distance analyses show that the average distance of the Cytb sequence of each sample within Ficus pumila L. pumila pollinator or within Ficus pumila var. awkeotsang pollinator is 0.0054 or 0.0164. The average genetic distance of the Cytb sequence between the two pollinator groups is 0.1385. The average genetic distance of the COI sequence of each sample within Ficus pumila var. pumila or Ficus pumila var. awkeotsang is 0.0048 or 0.0102, while the average genetic distance between the two wasp populations is 0.1896. Since the genetic distance between the two wasp groups are significantly greater than the genetic distance within the respective group, these data suggest that the two groups of fig wasps have differentiated during the evolution and reached to the level of species identification, namely the pollinators of Ficus pumila var. pumila and Ficus pumila var. awkeotsang are the two different wasp species.