基于12S,16S和28S rRNA基因序列的中国小毛瓢虫属系统发育分析

Phylogenetic analysis of the genus Scymnus Kugelann (Coleoptera: Coccinellidae) from China based on 12S, 16S and 28S rRNA gene sequences

【目的】小毛瓢虫属Scymnus Kugelann昆虫主要捕食蚜虫、蚧虫等害虫,是一类经济上重要的天敌昆虫。目前针对小毛瓢虫属的系统发育研究尚属空白,亚属之间的系统演化关系尚不明确,为了建立合理的分类系统,亟需对小毛瓢虫属的亲缘关系进行研究和探讨。【方法】以华南农业大学馆藏的小毛瓢虫属5亚属共44种为研究对象,采用PCR技术对12S, 16S和28S rRNA基因的部分序列进行扩增;运用MEGA 7.0分析了小毛瓢虫属内12S, 16S和28S rRNA基因的碱基组成,基于K2P模型计算了小毛瓢虫属44种的种间遗传距离;采用最大似然法(maximum-likelihood, ML)和贝叶斯推断法(Bayesian-inference, BI)构建该属的系统发育树。【结果】扩增获得小毛瓢虫属44种的12S rRNA基因序列平均长度为356 bp, 16S rRNA基因序列平均长度为351 bp, 28S rRNA基因序列平均长度为315 bp;序列分析表明,12S rRNA基因的A, T, G和C平均含量分别为38.8%, 43.5%, 11.9%和5.8%, 16S rRNA基因的A, T, G和C平均含量分别为37.6%, 40.3%, 14.4%和7.7%, 28S rRNA基因的A, T, G和C平均含量分别为26.7%, 18.3%, 31.4%和23.5%;基于联合序列分析的种间遗传距离为0.004～0.276,平均遗传距离为0.115。系统发育分析结果表明,小毛瓢虫属为单系起源,而小毛瓢虫亚属Scymnus(Scymnus) Kugelann、毛瓢虫亚属Scymnus(Neopullus) Sasaji、小瓢虫亚属Scymnus(Pullus) Mulsant和拟小瓢虫亚属Scymnus(Parapullus) Yang均为并系起源。【结论】基于12S, 16S和28S rRNA基因序列的小毛瓢虫属系统发育分析显示传统的形态学分类体系与基于分子数据分析的结果部分不一致,这表明应该对该属内各亚属的鉴别特征进行全面检视,筛选并确立各亚属的形态指标,同时也表明该属内的亚属分类单元需重新厘定。

【Aim】 The genus Scymnus Kugelann is one of the most economically significant genera of natural enemy insects due to its predatory activity against pests including scale insects and aphids. However, the classification of this genus is still ambiguous, and the relationship of the subgenera within this genus is still in dispute. In order to establish a reasonable classification system of the genus Scymnus , the phylogenetic analysis is needed to further refine the taxonomic status of the subgenera within this genus.【Methods】 The partial sequences of 12S, 16S and 28S rRNA genes from 44 species belonging to five subgenera within the genus Scymnus preserved in the Collection of South China Agricultural University were amplified using PCR. The inter-species genetic distance among the Scymnus species was calculated based on Kimura-2-parameter model using MEGA 7.0. The base composition of 12S rRNA, 16S rRNA and 28S rRNA genes was analyzed by using MEGA 7.0. The phylogeny trees were generated by maximum-likelihood (ML) and Bayesian-inference (BI) methods.【Results】 The mean length of the 12S, 16S and 28S rRNA gene sequences amplified from the 44 species of Scymnus are 356, 351 and 315 bp, respectively. The average contents of A, T, G and C of 12S rRNA gene sequence are 38.8%, 43.5%, 11.9% and 5.8%, respectively, those of 16S rRNA gene sequence are 37.6%, 40.3%, 14.4%, and 7.7%, respectively, and those of 28S rRNA gene sequence are 26.7%, 18.3%, 31.4% and 23.5%, respectively. The inter-species genetic distance is 0.004-0.276 based on the concatenated sequence data, and the average genetic distance is 0.115. The phylogenetic analysis revealed that the genus Scymnus is monophyletic, while the subgenera Scymnus (Scymnus ) Kugelann, Scymnus (Neopullus ) Sasaji, Scymnus (Pullus ) Mulsant and Scymnus (Parapullus ) Yang are paraphyletic.【Conclusion】 The phylogenetic analysis of Scymnus based on 12S, 16S and 28S rRNA gene sequences illustrated that the molecular classification system of this genus is not consistent well with its morphological classification system. In order to establish a reasonable classification system, other valid morphological characteristics should be explored to distinguish the relationships among the subgenera. Moreover, more research is needed to further refine the taxonomic status of the subgenera.