|Place of Conferral||中国科学院海洋研究所|
牡蛎是我国乃至全世界重要的经济贝类之一，但由于其贝壳易受外部环境因素影响，缺少明显的量化特征，导致分类上存在很多争议。前期的分类学研究多集中在常见种及经济种较多的巨蛎属Crassostrea和鉴定极为困难的小蛎属Saccostrea中，而对于其他科属的分类研究相对较少。本次研究综合利用传统形态分类方法和分子生物学技术，对中国近海缘曲牡蛎科Gryphaeidae、牡蛎科Ostreidae - 牡蛎亚科Ostreinae和脊牡蛎亚科Lophinae的常见种类以及它们的分类地位和分布特征进行了分析；综合利用本研究获得的线粒体基因组序列和NCBI收录的牡蛎种类序列，分析了牡蛎总科Ostreoidea不同科、属间的系统演化关系，为中国近海牡蛎分类系统的完善和修订提供了参考。同时，对猫爪牡蛎Crassostrea talonata 群体进行了系统地理学研究，初次揭示了该物种的群体遗传结构和可能的迁移路径，为认识牡蛎的进化提供了理论基础。主要结论如下：
1. 缘曲牡蛎科物种大多分布在浅水区至深水区的珊瑚礁上，通过系统的调查研究，确定的中国近海分布的缘曲牡蛎科种类包括3属7种。3属分别为：新硬牡蛎属Neopycnodonte、舌骨牡蛎属Hyotissa和斑顶牡蛎属Numismoida。7种分别为：新硬牡蛎Neopycnodonte cochlear、舌骨牡蛎Hyotissa hyotis、中华牡蛎Hyotissa sinensis、异壳舌骨牡蛎Hyotissa inaequivalvis、覆瓦牡蛎Hyotissa inermis、Hyotissa sp.、斑顶牡蛎Numismoida numisma。在中国近海发现1未定种Hyotissa sp.，另记录了日本1未定种Parahyotissa sp.。根据斑顶牡蛎与其他属种形态特征和遗传学的差异，认为异壳舌骨牡蛎不是斑顶牡蛎的同物异名种，并支持将斑顶牡蛎亚属Numismoida提升为斑顶牡蛎属Numismoida。基于线粒体16S rRNA基因、核H3基因和核28S rRNA基因的分析，表明新硬牡蛎位于系统发育树的基部，属于较为古老的一支。斑顶牡蛎位于舌骨牡蛎属和拟舌骨牡蛎属之间，舌骨牡蛎和中华牡蛎遗传关系较近，异壳舌骨牡蛎和Hyotissa sp.遗传关系较近。初步厘清了中国近海缘曲牡蛎科物种组成、分布和不同属种的遗传关系。
2. 共鉴定出中国沿海分布的牡蛎亚科Ostreinae和脊牡蛎亚科Lophinae物种8属13种，其中牡蛎亚科5属8种，包括1新种新直立牡蛎Ostrea neostentina Hu et al., 2019和1新纪录种等边牡蛎Ostrea equestris Say, 1834。脊牡蛎亚科3属5种，包括1新种方圆牡蛎Dendostrea paraquadrata sp. nov.。牡蛎亚科和脊牡蛎亚科新种和新纪录种的发现丰富了中国沿海牡蛎的物种多样性。通过形态特征和分子标记的结合分析，认为脊牡蛎亚科物种壳表放射肋和褶皱较明显，并且亚科内物种在系统发育树中聚在一起，得到一定程度上的遗传支持，所以我们支持将牡蛎亚科和脊牡蛎亚科作为两个有效的亚科。
4. 猫爪牡蛎群体（中国沿海19个群体，下载自NCBI的南美群体的序列）的系统地理学研究中，COI基因结果检测到三个分化显著的遗传谱系：lineage A、lineage B、lineage C，可细分为6个遗传显著性单元ESU 1-6。猫爪牡蛎具有大而稳定的种群，在演化过程中，同群体内形成随机的谱系分化，lineage A与lineage B + C的分化时间处于上新世时期，群体演化历史较长，有效群体足够大，所以分化的谱系形成同域分布。lineage B与lineage C的分化处于更新世时期，与长牡蛎Crassostrea gigas gigas和福建牡蛎Crassostrea gigas angulata的分化时间接近，导致分化的地质事件有待确定。在南美群体检测到lineage A、lineage C两个谱系，但南美群体的多样性低于中国沿海群体，且高比例的单倍型与青岛和威海共享，所以推测南美群体源自于西太平洋，支持相关文献的推测即猫爪牡蛎可能在上世纪通过漂流或附着于来往船只从亚洲扩张到南美。猫爪牡蛎线粒体COI各谱系的同域分布比例较高，导致核基因存在高频率的杂交和基因混合，所以核ITS2基因没有检测到分化。
Oysters are most important fishery and aquaculture species in China and all over the world. However, high morphological plasticity to externally environmental factors and lack of obvious quantitative characteristics, there are many controversial issues in classification. The previous taxonomic studies mainly focused on Crassostrea which including more economic and common species, and on Saccostrea which are difficult to be identified, but few on other families and genera. In this study, we analyzed the species numbers of Gryphaeidae and Ostreidae - subfamily Ostreinae and Lophinae, and their taxonomic status and distribution pattern based on the combination of traditionally morphological methods and molecular biological techniques. The phylogenetic relationships among different species, genera and families of Ostreoidea have been clarified through phylogenetic analysis based on the mitochondrial genome sequences obtained in this study and recorded in NCBI. Which provide reference for improving and revising the classification system of oysters in China. Molecular phylogeography of Crassostrea talonata populations were studied. The genetic structure and possible migration path of this species were revealed for the first time, which provided a theoretical basis for understanding the evolution of oysters. The main conclusions are as follows:
1. Gryphaeidae species are mostly distributed in the coral reefs from shallow waters to deep waters. Through systematic investigation and study, we identified 3 genera (Neopycnodonte, Hyotissa, and Numismoida) and 7 species (Neopycnodonte cochlear, Hyotissa hyotis, Hyotissa sinensis, Hyotissa inaequivalvis, Hyotissa inermis, Hyotissa sp., Numismoida numisma) of Gryphaeidae distributed along coast of China. An unassigned species - Hyotissa sp. was found from Weizhou Island, Guangxi province, China, and an unassigned species - Parahyotissa sp. was found from Japan. According to the morphological characteristics and genetic differences between Numismoida and other genera, Numismoida is elevated to a valid genus from subgenus Numismoida of Parahyotissa Harry, 1985. We consider Hyotissa inaequivalvis as a valid species based on the genetic and morphological differences with Numismoida numisma. Based on the analysis of mitochondrial 16S rRNA gene, nuclear H3 gene and nuclear 28s rRNA gene, Neopycnodonte cochlear is located at the base of phylogenetic tree and belongs to an older branch. In the phylogenetic trees, Numismoida numisma is embed between Hyotissa and Parahyotissa. The genetic relationship between Hyotissa hyotis and Hyotissa sinensis is relatively close, and so to Hyotissa inaequivalvis and Hyotissa sp.. The species composition, distribution and genetic relationship of different genera and species of the Gryphaeidae along coast of China were preliminarily clarified.
2. Along coast of China, we make sure there are 13 valid species in 8 genera of subfamily Ostreinae and Lophinae. 8 species in 5 genera of subfamily Ostreinae, including a new species - Ostrea neostentina Hu et al., 2019, and a new record species - Ostrea equestris say, 1834. 5 species in 3 genera of subfamily Lophinae, including a new species - Dendostrea paraquadrata sp. nov.. The discoveries of new species and new record species increased the species diversity of oysters in China. Based on the analysis of morphological characteristics and molecular markers, we support that subfamily Ostreinae and subfamily Lophinae are two effective subfamilies, as the radiation ribs and folds on the shell surface of the subfamily Lophinae are obvious, and the species in this subfamily gather together in the phylogenetic trees, and get some genetic supports.
3. Based on the mitochondrial genomes of 19 oyster species published in NCBI, and the mitochondrial genomes of Hyotissa hyotis, Dendostrea sandvichensis, Nanostrea exigua, Planostrea pestigris and Crassostrea talonata obtained in this study, the comparative phylogenetic analysis of Ostreoidea was carried out. The results show that only nad5-nad6 gene block in the mitochondrial genomes of Gryphaeidae and Ostreidae is conserved, the differentiation between the two families may be related to the differences of their living environment. In the phylogenetic trees reconstructed with mitochondrial coding genes and rRNA genes, the subfamily Ostreinae clustered together with subfamily Lophinae, and then with subfamily Saccostreinae, and subfamily Crassostreinae in turn. The gene composition and gene order of mitochondrial genomes of subfamily Ostreinae and subfamily Lophinae are highly consistent, which of different species in the subfamily Saccostreinae are consistent too. While in the subfamily Crassostreinae, except for the gene order of protein coding genes are consistent, the composition and arrangement of non-coding regions, tRNAs and rRNAs are quite different. "Tandem duplication - random loss" of genes might be an important mechanism for mitochondrial genome rearrangement. The emergence of many families and genera of oyster could be dated back to the Cretaceous, so it is believed that the diversity of oyster species was caused by the combination of geographical isolation, and different environmental adaptability of species.
4. Phylogeographic studies (19 populations from coastal China, sequences of South America were downloaded from NCBI) of Crassostrea talonata populations showed that, three genetic lineages with significant differentiation were detected in COI gene: lineage A, lineage B, and lineage C. The three genetic lineages could be subdivided into six genetic significance units ESU 1-6. The divergence time between lineage A and lineage B + C could be dated back to Pliocene, during the long evolutionary history, random lineages differentiated within the large stable population. The effective population was large enough, so the differentiated lineages could be distribute sympatric. The divergence time between lineage B and lineage C could be dated back to Pleistocene, which is close to that between the two subspecies Crassostrea gigas gigas and Crassostrea gigas angulata. The geological event leading to the differentiation of lineage B and lineage C remains to be confirmed, as the original source of lineage C has not been determined. Two lineages: lineage A and lineage C, were detected in the South American populations, high proportion haplotypes were shared with Qingdao and Weihai populations, and the diversity of South American populations is lower than that of Chinese populations. Therefore, we speculated that the South American populations were derived from western Pacific, which support previous speculation that C. talonata reached South America through rafting or fouling the hulls or keel of ships coming from Asia during the last century. The sympatric distribution ratio of mitochondrial COI lineages of Crassostrea talonata was relatively high, leading to high frequency hybridization and gene mixing of nuclear genes. Which might be the reason why no differentiation of nuclear ITS2 gene was identified.
|MOST Discipline Catalogue||理学 ; 理学::海洋科学 ; 理学::生物学|
|胡利莎. 中国近海缘曲牡蛎科和其他部分属种的分类及猫爪牡蛎系统地理学研究[D]. 中国科学院海洋研究所. 中国科学院大学,2020.|
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