Diversity of symbiotic algae of the genus Symbiodinium in scleractinian corals of the Xisha Islands in the South China Sea

Symbiotic algae （Symbiodinium sp.） in scleractinian corals are important in understanding how coral reefs will respond to global climate change. The present paper reports on the diversity of Symbiodinium sp. in 48 scleractinian coral species from 25 genera and 10 families sampled from the Xisha Islands in the South China Sea, which were identified with the use of restriction fragment length polymorphism （RFLP） of the nuclear ribosomal DNA large subunit gene （rDNA）. The results showed that： （i） Symbiodinium Clade C was the dominant zooxanthellae in scleractinian corals in the Xisha Islands; （ii） Symbiodinium Clade D was found in the corals Montipora aequituberculata, Galaxea fascicularis, and Plerogyra sinuosa; and （iii） both Symbiodinium Clades C and D were found simultaneously in Montipora digitata, Psammocora contigua, and Galaxeafascicularis. A poor capacity for symbiosis polymorphism, as uncovered by RFLP, in the Xisha Islands indicates that the scleractinian corals have low adaptability to environmental changes. Further studies are needed to investigate zooxanthellae diversity using other molecular markers.     

南海主要珊瑚礁水域的鱼类物种多样性研究

根据2004年5–7月和2005年3–4月采用深水三重刺网在南海的羚羊礁、华光礁、银砾滩、东岛、滨湄滩、排洪滩、本固暗沙、比微暗沙、武勇暗沙、海鸠暗沙、双子群礁、中业群礁、鲎藤礁、美济礁、仁爱礁、仙宾礁、南方浅滩、棕滩、大渊滩、永署礁、南薰礁、牛轭礁、道明群礁等23座主要珊瑚礁过渡性水域进行的2个航次专业调查资料, 分析了南海主要珊瑚礁水域的鱼类种类组成和群落特征。结果表明, 在珊瑚礁水域软骨鱼类以真鲨目和鲼目的种类数占优势, 硬骨鱼类以鲈形目和鲀形目的种类数占优势。相对重要指数(IRI)大于500的鱼类定为优势种, 西沙群岛有5种, 分别为迈氏条尾魟(Taeniura meyeni)、长吻裸颊鲷(Lethrinus miniatus)、胡椒鲷(Plectorhinchus pictus)、黄斑胡椒鲷(P. flavomaculatus)和灰六鳃鲨(Hexanchus griseus); 中沙群岛有6种, 分别为黄斑胡椒鲷、迈氏条尾魟、圆燕鱼(Platax orbicularis)、密斑刺鲀(Dioson hystrix)、红裸颊鲷(Lethrinus rubrioperculatus)和胡椒鲷; 南沙群岛有3种, 分别为黑梢真鲨(Carcharhinus limbatus)、灰三齿鲨(Triaenodon obesus)和星点鲹(Caranx stellatus)。针对南海珊瑚礁水域鱼类个体大小悬殊的特点, 本文分别以个体数和生物量为基础计算该水域的Margalef丰富度指数、Shannon-Wiener多样性指数、Simpson多样性指数和Pielou均匀度指数。物种组成的区域差异分析结果表明, 各珊瑚礁水域的鱼类物种无论与南海北部陆架海域还是与南沙西南陆架区相比都有明显的差异, 而属于相同生境类型水域的鱼类物种相似性较高。     

Cohesive molecular genetic data delineate species diversity in the dinoflagellate genus Symbiodinium

The diversity of symbiotic dinoflagellates ( Symbiodinium ) in pocilloporid corals originating from various reef habitats surrounding Heron Island, southern Great Barrier Reef, was examined by targeting ribosomal, mitochondrial, and chloroplast genes using six methods that analyse for sequence differences. The ability of each of 13 genetic analyses to characterize eight ecologically distinct Symbiodinium spp. was dependent on the level of conservation of the gene region targeted and the technique used. Other than differences in resolution, phylogenetic reconstructions using nuclear and organelle gene sequences were complementary and when combined produced a well-resolved phylogeny. Analysis of the ribosomal internal transcribed spacers using denaturing gradient gel electrophoresis fingerprinting in combination with sequencing of dominant bands provided a precise method for rapidly resolving and characterizing symbionts into ecologically and evolutionarily distinct units of diversity. Single-stranded conformation polymorphisms of the nuclear ribosomal large subunit (D1/D2 domain) identified the same number of ecologically distinct Symbiodinium spp., but profiles were less distinctive. The repetitive sequencing of bacterially cloned ITS2 polymerase chain reaction amplifications generated numerous sequence variants that clustered together according to the symbiont under analysis. The phylogenetic relationships between these clusters show how intragenomic variation in the ribosomal array diverges among closely related eukaryotic genomes. The strong correlation between phylogenetically independent lineages with different ecological and physiological attributes establishes a clear basis for assigning species designations to members of the genus Symbiodinium .     

Functional significance of genetically different symbiotic algae Symbiodinium in a coral reef symbiosis

The giant sea anemone Condylactis gigantea associates with members of two clades of the dinoflagellate alga Symbiodinium, either singly or in mixed infection, as revealed by clade-specific quantitative polymerase chain reaction of large subunit ribosomal DNA. To explore the functional significance of this molecular variation, the fate of photosynthetically fixed carbon was investigated by (14)C radiotracer experiments. Symbioses with algae of clades A and B released ca. 30-40% of fixed carbon to the animal tissues. Incorporation into the lipid fraction and the low molecular weight fraction dominated by amino acids was significantly higher in symbioses with algae of clade A than of clade B, suggesting that the genetically different algae in C. gigantea are not functionally equivalent. Symbioses with mixed infections yielded intermediate values, such that this functional trait of the symbiosis can be predicted from the traits of the contributing algae. Coral and sea anemone symbioses with Symbiodinium break down at elevated temperature, a process known as 'coral bleaching'. The functional response of the C. gigantea symbiosis to heat stress varied between the algae of clades A and B, with particularly depressed incorporation of photosynthetic carbon into lipid of the clade B algae, which are more susceptible to high temperature than the algae of clade A. This study provides a first exploration of how the core symbiotic function of photosynthate transfer to the host varies with the genotype of Symbiodinium, an algal symbiont which underpins corals and, hence, coral reef ecosystems.     

Fine-scale diversity and specificity in the most prevalent lineage of symbiotic dinoflagellates (Symbiodinium, Dinophyceae) of the Caribbean

The success of coral reefs is due to obligate mutualistic symbioses involving invertebrates and photosynthetic dinoflagellate symbionts belonging to the genus Symbiodinium. In the Caribbean, the vast majority of octocorals and other invertebrate hosts associate with Symbiodinium clade B, and more selectively, with a single lineage of this clade, Symbiodinium B1/B184. Although B1/B184 represents the most prevalent Symbiodinium in the Caribbean, there is little evidence supporting fine-scale diversity and host-alga specificity within this lineage. We explored simultaneously the questions of diversity and specificity in Symbiodinium B1/B184 by sequencing the flanking regions of two polymorphic microsatellites from a series of Symbiodinium clade B cultures along with Symbiodinium B1/B184 populations of the octocorals Pseudopterogorgia elisabethae, P. bipinnata and Gorgonia ventalina. Seven unique sequence variants were identified based on concatenation of the two loci. Phylogenetic analyses of these variants, which we refer to as phylotypes, recognized five as belonging to B1/B184, thus providing the first evidence of distinct taxa within this Symbiodinium lineage. Furthermore, sympatric P. elisabethae and P. bipinnata at San Salvador in the Bahamas were found to harbour distinct Symbiodinium B1/B184 phylotypes, demonstrating unequivocally the existence of fine-scale specificity between Caribbean octocorals and these algae. Taken together, this study exemplifies the complex nature of Symbiodinium biodiversity and specificity.     

Symbiont diversity in scleractinian corals from tropical reefs and subtropical non-reef communities in Taiwan

We examined zooxanthellae diversity in scleractinian corals from southern Taiwan and the Penghu Archipelago, a tropical coral reef and a subtropical non-reefal community, respectively. Zooxanthellae diversity was investigated in 52 species of scleractinian corals from 26 genera and 13 families, using restriction fragment length polymorphism (RFLP), and phylogenetic analyses of the nuclear small-subunit ribosomal DNA (nssrDNA) and large-subunit ribosomal DNA (nlsrDNA). RFLP and phylogenetic analyses of nuclear-encoded ribosomal RNA genes showed that Symbiodinium clade C was the dominant zooxanthellae in scleractinian corals in the seas around Taiwan; Symbiodinium clade D was also found in some species. Both Symbiodinium clade C and D were found in colonies of seven species of scleractinian corals. Symbiodinium clade D was associated with corals that inhabit either shallow water or the reef edge in deep water, supporting the hypothesis that Symbiodinium clade D is a relatively stress-tolerant zooxanthellae found in marginal habitats.Communicated by Biological Editor H.R. Lasker     

Dinoflagellate cyst distribution along a shelf to slope transect of an oligotrophic tropical sea (Sunda Shelf, South China Sea)

From 51 surface samples collected along a shelf to slope transect of the Sunda Shelf, South China Sea, 36 taxa of organic‐walled dinoflagellate cysts are identified. Oligotrophic tropical shelf assemblages on the Sunda Shelf are dominated by gonyaulacoids such as Spiniferites species, Operculodinium centmcarpum and Operculodinium israelianum. Concentrations of dinoflagellate cysts in the shelf sediments are generally low and correlate well with the content of fine‐grained (clay and silt fraction) sediments. Detailed comparisons of sediment grain‐size distributions to concentrations of dominant dinoflagellate taxa (Spiniferites species, 0. centmcarpum and 0. israelianum) in the shelf sediments indicate that these taxa behave in water like sediment particles with size range φ 5.75–6.25 (13–18 μm). In contrast, slope assemblages in fine‐grained sediments are dominated by protoperidinioids. This may reflect higher nutrient availability as a result of weak winter upwelling. The concentrations of dinoflagellate cysts in the shelf sediments are mainly controlled by transport and winnowing processes and are probably not representative of surface water conditions.     

运用PCR-RFLP方法研究三亚鹿回头岸礁造礁石珊瑚共生藻的组成

造礁石珊瑚共生藻的系统分类研究对于理解珊瑚礁生态系统对全球变化的响应具有十分重要的意义.本研究利用PCR技术扩增核糖体基因人亚基片段以及限制性片段长度多态性(RFLP)的方法,对海南三亚鹿回头岸礁的8科14属22种造礁石珊瑚的共生藻组成进行了研究.结果表明鹿回头岸礁造礁石珊瑚共生藻以C系群为优势系群,偶尔发现D系群与鹿角杯形珊瑚(Pocilolpora damieornis)和黄癣蜂巢珊瑚(Favia favus)共生:另外丑鹿角珊瑚(Acropora horrida)和丛生盔形珊瑚(Galaxea fascicularis)可以同时与C系群和D系群共生.共生多型性的发现暗示珊瑚与共生藻的共生关系具有灵活性.研究结果同样显示共生藻的核糖体基因人片段的DNA多态性偏低.未来应该结合其他的分子标记对鹿回头岸礁造礁石珊瑚共生藻的DNA多态性进行更深入的研究.     

Microsatellite loci for assessing genetic diversity, dispersal and clonality of coral symbionts in 'stress-tolerant' clade D Symbiodinium

Reef corals harbouring clade D Symbiodinium spp. (endosymbiotic dinoflagellates) appear more tolerant of environmental stress. As sea surface temperatures rise, symbioses involving Symbiodinium D may increase in prevalence. For this reason, eight polymorphic microsatellite loci were developed for clade D Symbiodinium. From the analysis of 132 samples originating from cnidarian hosts in the Atlantic, Pacific and Indian Oceans, 4 to 35 alleles were found at each haploid locus and diversity indices ranged from 0.35 to 0.97. Population genetic analyses of these symbionts should reveal how environmental perturbations affect genetic diversity, geographical distributions, and possible host-range expansions to new coral species.     

海南岛中华蜜蜂遗传多样性的微卫星DNA分析

为了解海南岛中华蜜蜂Apis cerana cerana的遗传多样性和遗传结构及其与大陆种群的关系, 本研究应用10个微卫星DNA标记对海南岛11个地点627个蜂群的627头工蜂样本和大陆2个地点102个蜂群的102头工蜂样本进行了分析。结果表明： 海南岛中华蜜蜂遗传多样性较高, 单个位点检测到等位基因5～17个; 各种群平均等位基因数为4.5～7.0个, 平均杂合度为0.59～0.65。海南岛中华蜜蜂在10个位点上表现出相似遗传结构, 文昌和屯昌种群在AT101位点的等位基因频率较特殊。岛内 岛外中华蜜蜂的遗传分化系数F_ST范围为0.06～0.13; 文昌、 屯昌种群分别同海南岛内其他9个种群的F_ST（0.06～0.12）大于这9个种群间的FST（0～0.05）。海南岛中华蜜蜂同邻近大陆种群发生了明显的遗传分化; 除文昌、 屯昌种群发生中等程度的分化外, 海南岛内其他种群之间遗传分化较小。本研究结果对海南岛中华蜜蜂资源的保护和合理利用具有重要的指导意义。     

Molecular diversity of symbiotic algae (zooxanthellae) in scleractinian corals of Kenya

In this first sequence analysis of ‘zooxanthellae’ (symbiotic algae of the genus Symbiodinium) in scleractinian corals in Africa, seven Kenyan species sampled in 2001–2002 were analysed by RFLP and sequencing of a PCR-amplified fragment of the LSU rRNA gene. Zooxanthellae of phylotypes A, C and D, all described previously in corals from other regions of the world, were detected. All sequences of phylotype D were identical, while phylotype C was variable, with 14 distinct sequences, seven of which clustered in a previously unreported subgroup of phylotype C, among the 22 samples. These data on the diversity of zooxanthellae in Kenyan corals 3–4 years after the 1998 bleaching event are of potential value for longitudinal studies of temporal changes in zooxanthella diversity in Kenyan corals, especially in relation to future large-scale bleaching episodes.     

Identity and diversity of coral endosymbionts (zooxanthellae) from three Palauan reefs with contrasting bleaching, temperature and shading histories

The potential of corals to associate with more temperature-tolerant strains of algae (zooxanthellae, Symbiodinium) can have important implications for the future of coral reefs in an era of global climate change. In this study, the genetic identity and diversity of zooxanthellae was investigated at three reefs with contrasting histories of bleaching mortality, water temperature and shading, in the Republic of Palau (Micronesia). Single-stranded conformation polymorphism and sequence analysis of the ribosomal DNA internal transcribed spacer (ITS)1 region was used for genotyping. A chronically warm but partly shaded coral reef in a marine lake that is hydrographically well connected to the surrounding waters harboured only two single-stranded conformation polymorphism profiles (i.e. zooxanthella communities). It consisted only of Symbiodinium D in all 13 nonporitid species and two Porites species investigated, with the remaining five Porites harbouring C*. Despite the high temperature in this lake (> 0.5 degrees above ambient), this reef did not suffer coral mortality during the (1998) bleaching event, however, no bleaching-sensitive coral families and genera occur in the coral community. This setting contrasts strongly with two other reefs with generally lower temperatures, in which 10 and 12 zooxanthella communities with moderate to low proportions of clade D zooxanthellae were found. The data indicate that whole coral assemblages, when growing in elevated seawater temperatures and at reduced irradiance, can be composed of colonies associated with the more thermo-tolerant clade D zooxanthellae. Future increases in seawater temperature might, therefore, result in an increasing prevalence of Symbiodinium phylotype D in scleractinian corals, possibly associated with a loss of diversity in both zooxanthellae and corals.     

Non-seasonal clade-specificity and subclade microvariation in symbiotic dinoflagellates (Symbiodinium spp.) in Zoanthus sansibaricus (Anthozoa: Hexacorallia) at Kagoshima Bay, Japan

While much work has investigated the genetic diversity of symbiotic dinoflagellate genus Symbiodinium Freudenthal in cnidarians, investigations into such diversity over temporal scales (seasonal and/or annual) remain scarce. Here, we have sequenced the internal transcribed spacer of ribosomal DNA (ITS‐rDNA) of Symbiodinium from samples of designated Zoanthus sansibaricus Carlgren (Anthozoa: Hexacorallia) colonies collected for 12 months (August 2004–July 2005) at a high latitude non‐reefal coral community at Sakurajima, Kagoshima Bay, Japan (31°35′N, 130°35′E). Our results show that despite large ocean temperature changes (15.0–29.0°C) throughout the one‐year experimental period, Z. sansibaricus colonies contained only clade C Symbiodinium from many different subclade C1/C3‐related novel types not previously reported. While no temporal changes in clade‐level associations were seen, there were consistent and extremely large amounts (145 unique sequences out of 153 total obtained sequences) of genotypic microvariation observed in our obtained sequences. Despite Z. sansibaricus acquiring Symbiodinium horizontally and the presence of various other Symbiodinium clades (A, G) and subclades (e.g. C15 and derived subclades) in the immediate environment, Z. sansibaricus at Sakurajima specifically associates with subclade C1/C3‐related Symbiodinium. While subclades C1/C3 have been found in a variety of different environments and are believed to be ancestral, ‘generalist’ types of Symbiodinium, C1/C3‐related clades such as seen here may be more adapted to specialized niches. We theorize that specific and year‐round association with many different types of subclade C1/C3‐related Symbiodinium helps Z. sansibaricus to survive in the fluctuating Sakurajima environment.     

PCP gene family in Symbiodinium from Hippopus hippopus: low levels of concerted evolution,isoform diversity,and spectral tuning of chromophores

Photosynthetic dinoflagellates have evolved unique water-soluble light harvesting complexes known as peridinin-chlorophyll a-binding proteins (PCPs). Most species of dinoflagellates express either 14 to 17 kDa or 32 to 35 kDa mature PCP apoproteins and do so in stable combinations of isoforms that differ in isoelectric point (pI). The source (posttranslational modification, protein degradation, or genetic) and functional significance of PCP isoform variation have remained unclear. PCPs are encoded by multigene families. However, previous reports conflict over the diversity of PCP genes within gene arrays. We present the first genomic characterization of the PCP gene family from a symbiotic dinoflagellate. Symbiodinium from the Pacific bivalve Hippopus hippopus (203) contains genes for 33 kDa PCP apoproteins that are organized in tandem arrays like those of free-living dinoflagellates Amphidinium carterae, Lingulodinium (Gonyaulax) polyedra, and Heterocapsa pygmaea. The Symbiodinium 203 PCP cassette consists of 1,098-bp coding regions separated by approximately 900-bp spacers. The spacers contain a conserved upstream sequence similar to the promoter in L. polyedra. Surprisingly, sequences of cloned coding regions are not identical, and can differ at up to 2.2% of the nucleotide sites. Sequence variation is found at both silent and nonsilent sites, and analysis of cDNA clones indicate that the variation is present in the mRNA pool. We propose that this variation represents nucleotide diversity among PCP gene copies that are evolving under low-level concerted evolution. Interestingly, the predicted proteins have pIs that are within the range of those published for other species of Symbiodinium. Thus, posttranslational modifications are not necessary to explain the multiple PCP isoforms. We have also identified several polymorphic sites that may influence spectral absorption tuning of chromophores.     

福建东山石珊瑚伴生物种多样性

本文记录了福建东山锯齿刺星珊瑚(Cyphastrea serrailia)、标准菊花珊瑚(Favia speciosa)和盾形陀螺珊瑚(Turbinaria peltata)等6种造礁石珊瑚。石珊瑚的立体生境中,栖息着埋栖、穴栖、缝栖、附着和游动等5种栖息习性的154种伴生物种。埋栖的连贵藤壶和穴栖的羽膜石蛏、珊瑚绒贻贝等是造礁石珊瑚伴生物种的表征。     

海南岛热带森林景观类型多样性

依据景观生态学原理,按地貌、气候、土壤、植被和土地利用方式的分异,以带、域、省、区、类型为5个基本单位及亚、组等为辅助单位,组建海南岛热带森林景观类型分类体系。把海南岛热带森林景观作为省级单位,它隶属于全球热带林景观带、亚洲（东方）热带林景观域、中国热带林景观亚域,其下划分为东部潮湿森林景观、西部半干旱森林景观、中南部山地森林景观、热带常绿针叶林景观、热带竹林景观和热带人工林景观6个森林景观区;以热带低地沟谷热带雨林为代表的11个森林景观亚区;以热带低地沟谷龙脑香森林景观为代表的26个森林景观类型组;以热带低地沟谷青皮林为代表的54个森林景观类型。海南岛热带森林景观类型分类体系较全面地表达了海南岛热带森林景观类型多样性。     

Genetic diversity and genetic structure of Decalobanthus boisianus in Hainan Island,China

Decalobanthus boisianus is a native plant of Hainan Island, China, which has caused considerable damage to tropical forest ecosystems in recent decades. Understanding the genetic diversity and structure of this species can facilitate uncovering the molecular mechanism of its invasive ability. Here, we collected 77 individuals of D. boisianus spanning 8 distribution areas with a gradient of human disturbance intensity (i.e., low, moderate, and high disturbance intensity groups) to assess patterns of genetic diversity and structure using inter simple sequence repeat (ISSR) markers. We found that a total of 220 loci were scored with 13 primers using ISSR methods, and that 198 loci were polymorphic. The genetic diversity of D. boisianus among these eight forests decreased with increasing human disturbance intensity. Over 70% of the total genetic variation was present within populations, while less than 30% of variation was found among populations. There was a high gene flow (1.27) among them due to a lack of effective geographic barriers. The mean Nei's genetic distance of D. boisianus populations was found to be relatively small (i.e., 0.07), and the average genetic similarity of the eight populations was high (i.e., 0.93). Our findings indicate that the genetic diversity of D. boisianus correlated to human disturbance density, and that D. boisianus populations in Hainan Island have frequent gene exchange. We suggest that reduce deforestation to decrease human disturbance may be a good way to prevent the invasion of D. boisianus.