基于rDNAITS序列分析莲塘湖萼花臂尾轮虫两种形态型的分类地位
TAXONOMICAL STATUS OF TWO BRACHIONUS CALYCIFLORUS MORPHOTYPES IN LAKE LIANTANG BASED ON ITS SEQUENCE
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摘要: 轮虫的周期变形是指种群内出现的轮虫形态随时间推移而发生的周期性变化,包括轮虫个体大小的变化、轮虫后棘刺或后侧棘刺的有无及长度的变化等。广泛存在的周期变形使轮虫的分类更加复杂。利用分子标记对不同形态型轮虫的遗传分化进行研究将有助于正确认识它们的分类地位。为此,研究对采自芜湖市莲塘湖水体中萼花臂尾轮虫(Brachionus calyciflorus)30个有棘刺型(Spined morphotype)的克隆(S1-S30)和18个无棘刺型(Unspined morphotype)的克隆(U1-U18)进行了rDNA ITS序列分析;以十指臂尾轮虫(B.patulus)为外群,构建了48个克隆的系统发生树(NJ、MP、ML和贝叶斯树)。结果表明,所测48个克隆共包括16个单元型。在ITS序列中,T、C、A、G碱基的平均含量分别为28.6%、18.7%、35.9%、16.8%,其中A+T含量为64.5%,C+G含量为35.5%。单元型U12与其他单元型间的序列差异百分比为26.2%-26.6%,平均为26.47%;其中,发生在ITS1、5.8S和ITS2区间的序列差异百分比分别为26.9%-27.8%、2.9%-3.5%和44.4%-45.0%,平均依次为27.27%、3.09%和44.48%。而其他单元型间平均序列差异百分比为0.41%。4个系统树均支持将48个克隆分为2个支系:无棘刺型克隆U12独成一支,无棘刺型的其余克隆与所有有棘刺型克隆构成另一支系。单元型U12与其他单元型应分别属于两个不同的姐妹种;但两种形态型并非不同的亚种或互为姐妹种,它们间的形态差异主要由表型可塑性引起。Abstract: Cyclomorphosis of rotifer defines the temporal cyclic morphological changes that occur within a rotifer population, including variation in body size, presence or absence and lengths of lateral spines and posteriolateral spines. This widespread phenomenon has complicated rotifer taxonomy. The study on genetic differentiation among different rotifer morphotypes by using molecular markers can help us to recognize their taxonomical status correctly. In the pre-sent study, the ITS sequences of 30 (S1-S30) spined and 18 (U1-U18) unspined Brachionus calyciflorus clones, col-lected from Lake Liantang, were analyzed, and their molecular phylogenetic trees were constructed by Neighbor-Joining (NJ), Maximum-Parsimony (MP), Maximum-Likelihood (ML) and Bayesian methods using B. patulus as an outgroup. The results showed that all the 48 clones belonged to 16 haplotypes. Within ITS sequence, the average content of T, C, A and G base was 28.6%, 18.7%, 35.9% and 16.8%, respectively. The content of A base plus T base was 64.5%, but that of C base plus G base was 35.5%. The sequence divergence was 26.2%-26.6% between haplotype U12 and the other haplotypes, with an average of 26.47%. The sequence divergence occurred in ITS1, 5.8S and ITS2 was 26.9%-27.8%, 2.9%-3.5% and 44.4%-45.0%, and the mean value was 27.27%, 3.09% and 44.48%, respectively. However, the av-erage sequence divergence was 0.41% among the other haplotypes. All the four phylogenetic trees supported that 48 clones should be obviously divided into two different clades. The first clade included clone U12, and the second one included all the spined clones and the other unspined clones. Haplotype U12 and the other haplotypes belonged to two sibling species, but the two B. calyciflorus morphotypes were not different subspecies or sibling species, and their variation in morphology attributed mainly to phenotypic plasticity.
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Keywords:
- Brachionus calyciflorus /
- Morphotype /
- ITS sequence /
- Phenotypic plasticity
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