中国13种海参系统发育和骨片演化分析

Molecular phylogeny and ossicle evolution analysis for 13 species of sea cucumber in China

运用扫描电子显微镜观察了中国沿海13种代表性海参的骨片,并获得了8种海参的线粒体16SrDNA基因序列,通过整合网上序列联合分析以期了解13种海参的系统发育关系和骨片演化规律。结果表明, 13种海参的骨片包括桌形体、假桌形体、扣状体、杆状体、穿孔板、花纹样体、颗粒体7种类型; 8种海参的16S rDNA片段长度在465 bp左右,富含AT碱基, A+T的含量平均为55.8%,符合无脊椎动物线粒体DNA序列的特征。从GenBank中获取11种海参16S rDNA基因序列,以杂色角孔海胆(Salmacis sphaeroides)为外群,联合本研究中所测序列构建了NJ和ME系统树。结果表明,NJ、ME系统发育树基本一致,海参科(Holothuriidae)内,柄体参属(Labidodemas)与海参属(Holothuria)亲缘关系极近且骨片形态均相似,可划分为同一个属;与传统形态学分类不同,刺参科(Stichopodidae)同尻参科(Caudinidae)、沙鸡子科(Phyllophoridae)、硬瓜参科(Sclerodactylidae)、瓜参科(Cucumariidae)聚成一簇,而与海参科亲缘关系较远,符合最新分类系统。本研究根据NJ和ME系统发育树结果,结合海参骨片的形态学资料,对海参科内骨片的演化进行了分析,认为虽然桌形体的进化史尚不清晰,但在海参科内,海参骨片由复杂的桌形体、扣状体向简单的花纹样体和颗粒体演化。

To fully determine the phylogenetic relationship and ossicle evolution of holothurians, the ossicles of 13 representative sea cucumber species in the China Sea were observed by scanning electronic microscopy and the mitochondrial 16S rDNA gene from eight specimens were amplified and sequenced. The results demonstrated that ossicles of the 13 sea cucumbers could be classified into seven types, which were termed as table, pseudo-table, button, rod, plate, rosette, and oblate grain. The length of 16S rDNA fragments amplified from eight sea cucum- bers was approximately 465 bp. These fragments were enriched in AT bases with an average A+T content of 55.8%, which is in accordance with the characteristics of mitochondrial DNA in invertebrates. 16S rDNA sequences of 11 sea cucumbers obtained from GenBank were combined with sequences from our study to construct a phylogenetic tree. Salmacis sphaeroides was regarded as a control group. Neighbor-joining (NJ) and minimum evolution (ME) methods provided almost identical results. Genetic relationships between Labidodemas and Holothuria in Holo- thuriidae were rather close and shapes of their ossicles were also similar, thus they could be divided into the same genus;Caudinidae, Phyllophoridae, Sclerodactylidae, and Cucumariidae were clustered with Stichopodidae, and separated from Holothuriidae. Contrary to traditional taxonomy, our study met the criteria of the newest taxonomy system, wherein Aspidochirotida was removed and Holothuroidea was redivided into seven orders, including Dendrochirotida, Synallactida, Molpadida, Persicalida, Holothuriida, Elasipodida, and Apodida. Based on mo- lecular phylogenetic trees and morphological data of ossicles, we hypothesized that ossicles of sea cucumbers in Holothuriidae underwent slow evolution from a complex shape, such as table and button, to simple patterns, such as rosette and oblate grain. Furthermore, considering that the rod in Holothuria pervicax and the button in Holothuria fuscocinerea, we concluded that ossicles in Holothuriidae underwent slow transition rather than direct evolution.