Importance of time and place: patterns in abundance of Symbiodinium clades A and B in the tropical sea anemone Condylactis gigantea

Molecular phylogeny and community fingerprinting of coral-associated Symbiodinium north of the Arabian Gulf

Understanding coral-Symbiodinium relationships including changes in the genotypes and the numbers of Symbiodinium can explain the ability of Kuwait coral to survive high fluctuations in water temperature. In the current study, the diversity of Symbiodinium associated with fourteen coral species from six reef systems south of Kuwait was investigated. The results proved the predominance of clade C members in all corals tested, which reflects the importance of this type in helping corals thrive in the Gulf's harsh conditions. Platygyra daedalea was the only coral found that harbored clades A, B and C in their tissue but it is the most vulnerable coral for bleaching. The total number of Symbiodinium-like cells in the seawater was 10(4) cell ml(-1) while in coral tissue and mucus 10(7) cell g(-1) and 10(7) cell ml(-1) were found, respectively, and a strong positive correlation with the seawater temperature, salinity and conductivity was found.

Microsatellite abundance across the Anthozoa and Hydrozoa in the phylum Cnidaria

BACKGROUND

Microsatellite loci have high mutation rates and thus are indicative of mutational processes within the genome. By concentrating on the symbiotic and aposymbiotic cnidarians, we investigated if microsatellite abundances follow a phylogenetic or ecological pattern. Individuals from eight species were shotgun sequenced using 454 GS-FLX Titanium technology. Sequences from the three available cnidarian genomes (Nematostella vectensis, Hydra magnipapillata and Acropora digitifera) were added to the analysis for a total of eleven species representing two classes, three subclasses and eight orders within the phylum Cnidaria.

RESULTS

Trinucleotide and tetranucleotide repeats were the most abundant motifs, followed by hexa- and dinucleotides. Pentanucleotides were the least abundant motif in the data set. Hierarchical clustering and log likelihood ratio tests revealed a weak relationship between phylogeny and microsatellite content. Further, comparisons between cnidaria harboring intracellular dinoflagellates and those that do not, show microsatellite coverage is higher in the latter group.

CONCLUSIONS

Our results support previous studies that found tri- and tetranucleotides to be the most abundant motifs in invertebrates. Differences in microsatellite coverage and composition between symbiotic and non-symbiotic cnidaria suggest the presence/absence of dinoflagellates might place restrictions on the host genome.

Bacterial communities in the gut and reproductive organs of Bactrocera minax (Diptera: Tephritidae) based on 454 pyrosequencing

The citrus fruit fly Bactrocera minax is associated with diverse bacterial communities. We used a 454 pyrosequencing technology to study in depth the microbial communities associated with gut and reproductive organs of Bactrocera minax. Our dataset consisted of 100,749 reads with an average length of 400 bp. The saturated rarefaction curves and species richness indices indicate that the sampling was comprehensive. We found highly diverse bacterial communities, with individual sample containing approximately 361 microbial operational taxonomic units (OTUs). A total of 17 bacterial phyla were obtained from the flies. A phylogenetic analysis of 16S rDNA revealed that Proteobacteria was dominant in all samples (75%–95%). Actinobacteria and Firmicutes were also commonly found in the total clones. Klebsiella, Citrobacter, Enterobacter, and Serratia were the major genera. However, bacterial diversity (Chao1, Shannon and Simpson indices) and community structure (PCA analysis) varied across samples. Female ovary has the most diverse bacteria, followed by male testis, and the bacteria diversity of reproductive organs is richer than that of the gut. The observed variation can be caused by sex and tissue, possibly to meet the host's physiological demands.

Increasing pCO2 correlates with low concentrations of intracellular dimethylsulfoniopropionate in the sea anemone Anemonia viridis

Marine anthozoans maintain a mutualistic symbiosis with dinoflagellates that are prolific producers of the algal secondary metabolite dimethylsulfoniopropionate (DMSP), the precursor of the climate-cooling trace gas dimethyl sulfide (DMS). Surprisingly, little is known about the physiological role of DMSP in anthozoans and the environmental factors that regulate its production. Here, we assessed the potential functional role of DMSP as an antioxidant and determined how future increases in seawater pCO₂ may affect DMSP concentrations in the anemone Anemonia viridis along a natural pCO₂ gradient at the island of Vulcano, Italy. There was no significant difference in zooxanthellae genotype and characteristics (density of zooxanthellae, and chlorophyll a) as well as protein concentrations between anemones from three stations along the gradient, V1 (3232 μatm CO₂), V2 (682 μatm) and control (463 μatm), which indicated that A. viridis can acclimate to various seawater pCO₂. In contrast, DMSP concentrations in anemones from stations V1 (33.23 ± 8.30 fmol cell⁻¹) and V2 (34.78 ± 8.69 fmol cell⁻¹) were about 35% lower than concentrations in tentacles from the control station (51.85 ± 12.96 fmol cell⁻¹). Furthermore, low tissue concentrations of DMSP coincided with low activities of the antioxidant enzyme superoxide dismutase (SOD). Superoxide dismutase activity for both host (7.84 ± 1.37 U·mg⁻¹ protein) and zooxanthellae (2.84 ± 0.41 U·mg⁻¹ protein) at V1 was 40% lower than at the control station (host: 13.19 ± 1.42; zooxanthellae: 4.72 ± 0.57 U·mg⁻¹ protein). Our results provide insight into coastal DMSP production under predicted environmental change and support the function of DMSP as an antioxidant in symbiotic anthozoans.

Host-specific interactions with environmental factors shape the distribution of symbiodinium across the Great Barrier Reef

Background

The endosymbiotic dinoflagellates (genus Symbiodinium) within coral reef invertebrates are critical to the survival of the holobiont. The genetic variability of Symbiodinium may contribute to the tolerance of the symbiotic association to elevated sea surface temperatures (SST). To assess the importance of factors such as the local environment, host identity and biogeography in driving Symbiodinium distributions on reef-wide scales, data from studies on reef invertebrate-Symbiodinium associations from the Great Barrier Reef (GBR) were compiled.

Methodology/Principal Findings

The resulting database consisted of 3717 entries from 26 studies. It was used to explore ecological patterns such as host-specificity and environmental drivers structuring community complexity using a multi-scalar approach. The data was analyzed in several ways: (i) frequently sampled host species were analyzed independently to investigate the influence of the environment on symbiont distributions, thereby excluding the influence of host specificity, (ii) host species distributions across sites were added as an environmental variable to determine the contribution of host identity on symbiont distribution, and (iii) data were pooled based on clade (broad genetic groups dividing the genus Symbiodinium) to investigate factors driving Symbiodinium distributions using lower taxonomic resolution. The results indicated that host species identity plays a dominant role in determining the distribution of Symbiodinium and environmental variables shape distributions on a host species-specific level. SST derived variables (especially SSTstdev) most often contributed to the selection of the best model. Clade level comparisons decreased the power of the predictive model indicating that it fails to incorporate the main drivers behind Symbiodinium distributions.

Conclusions/Significance

Including the influence of different host species on Symbiodinium distributional patterns improves our understanding of the drivers behind the complexity of Symbiodinium-invertebrate symbioses. This will increase our ability to generate realistic models estimating the risk reefs are exposed to and their resilience in response to a changing climate.

Sea anemones may thrive in a high CO2 world

Increased seawater pCO₂ , and in turn 'ocean acidification' (OA), is predicted to profoundly impact marine ecosystem diversity and function this century. Much research has already focussed on calcifying reef-forming corals (Class: Anthozoa) that appear particularly susceptible to OA via reduced net calcification. However, here we show that OA-like conditions can simultaneously enhance the ecological success of non-calcifying anthozoans, which not only play key ecological and biogeochemical roles in present day benthic ecosystems but also represent a model organism should calcifying anthozoans exist as less calcified (soft-bodied) forms in future oceans. Increased growth (abundance and size) of the sea anemone (Anemonia viridis) population was observed along a natural CO₂ gradient at Vulcano, Italy. Both gross photosynthesis (P_G ) and respiration (R) increased with pCO₂ indicating that the increased growth was, at least in part, fuelled by bottom up (CO₂ stimulation) of metabolism. The increase of P_G outweighed that of R and the genetic identity of the symbiotic microalgae (Symbiodinium spp.) remained unchanged (type A19) suggesting proximity to the vent site relieved CO₂ limitation of the anemones' symbiotic microalgal population. Our observations of enhanced productivity with pCO₂ , which are consistent with previous reports for some calcifying corals, convey an increase in fitness that may enable non-calcifying anthozoans to thrive in future environments, i.e. higher seawater pCO₂ . Understanding how CO₂ -enhanced productivity of non- (and less-) calcifying anthozoans applies more widely to tropical ecosystems is a priority where such organisms can dominate benthic ecosystems, in particular following localized anthropogenic stress.

Transmission mode predicts specificity and interaction patterns in coral-Symbiodinium networks

Most reef-building corals in the order Scleractinia depend on endosymbiotic algae in the genus Symbiodinium for energy and survival. Significant levels of taxonomic diversity in both partners result in numerous possible combinations of coral-Symbiodinium associations with unique functional characteristics. We created and analyzed the first coral-Symbiodinium networks utilizing a global dataset of interaction records from coral reefs in the tropical Indo-Pacific and Atlantic Oceans for 1991 to 2010. Our meta-analysis reveals that the majority of coral species and Symbiodinium types are specialists, but failed to detect any one-to-one obligate relationships. Symbiont specificity is correlated with a host’s transmission mode, with horizontally transmitting corals being more likely to interact with generalist symbionts. Globally, Symbiodinium types tend to interact with only vertically or horizontally transmitting corals, and only a few generalist types are found with both. Our results demonstrate a strong correlation between symbiont specificity, symbiont transmission mode, and community partitioning. The structure and dynamics of these network interactions underlie the fundamental biological partnership that determines the condition and resilience of coral reef ecosystems.

Symbiont communities and host genetic structure of the brain coral Platygyra verweyi, at the outlet of a nuclear power plant and adjacent areas

In the context of rising seawater temperatures associated with climate change, the issue of whether coral holobionts deal with this challenge by shuffling their associations with stress- and/or heat-tolerant Symbiodinium, by generating heat-resistant host genotypes, or both is important for coral survival. In this study, the composition of communities of the endosymbiont Symbiodinium and the population genetics of the coral host Platygyra verweyi were examined in a reef impacted by hot-water discharged from the outlet of a nuclear power plant in operation in Kenting, Southern Taiwan since 1984. The water at this site is 2.0-3.0 °C warmer than adjacent reefs in summer, which have an average seawater temperature of 29.0 °C. The data were compared with those for the same species at other sites within 12 km of the outlet site. Platygyra verwyei was associated with one or both of Symbiodinium types C3 (heat sensitive) and D1a (heat tolerant) at all sites with the latter being the dominant at the nuclear power plant outlet. The proportion of C3 in populations increased gradually with increasing distance from the hot-water discharge. Genetic analysis of the Platygyra verweyi host using mitochondrial and nuclear markers showed no genetic differentiation among sites. Changes in the composition of Symbiodinium types associated with P. verweyi among closely located sites in Kenting suggested that this coral might have acclimatized to the constant thermal stress by selective association with heat-tolerant Symbiodinium types, whereas the role of the host in adaptation was inconclusive.

Low-diversity bacterial community in the gut of the fruitfly Drosophila melanogaster

The bacteria in the fruitfly Drosophila melanogaster of different life stages was quantified by 454 pyrosequencing of 16S rRNA gene amplicons. The sequence reads were dominated by 5 operational taxonomic units (OTUs) at ≤ 97% sequence identity that could be assigned to Acetobacter pomorum, A. tropicalis, Lactobacillus brevis, L. fructivorans and L. plantarum. The saturated rarefaction curves and species richness indices indicated that the sampling (85,000-159,000 reads per sample) was comprehensive. Parallel diagnostic PCR assays revealed only minor variation in the complement of the five bacterial species across individual insects and three D. melanogaster strains. Other gut-associated bacteria included 6 OTUs with low %ID to previously reported sequences, raising the possibility that they represent novel taxa within the genera Acetobacter and Lactobacillus. A developmental change in the most abundant species, from L. fructivorans in young adults to A. pomorum in aged adults was identified; changes in gut oxygen tension or immune system function might account for this effect. Host immune responses and disturbance may also contribute to the low bacterial diversity in the Drosophila gut habitat.

Populations of Symbiodinium muscatinei show strong biogeographic structuring in the intertidal anemone Anthopleura elegantissima

Among temperate cnidarian symbioses, the partnership between the intertidal anemone Anthopleura elegantissima and its dinoflagellate and chlorophyte symbionts is one of the most well characterized. Biogeographic, reciprocal transplant, and physiological studies have convincingly demonstrated a relationship between environmental factors such as temperature and irradiance and the distribution of symbionts from both algal phyla. However, little is known about the fine-scale diversity or biogeographic distribution within symbiont lineages of this anemone. We used sequence information from the mitochondrial cytochrome b and chloroplast 23S ribosomal genes and restriction fragment length polymorphism data from the 18S nuclear ribosomal gene to characterize the Symbiodinium populations in tentacles clipped from 105 anemones at 14 sites along the entire California coast, spanning about 1200 km. Our results show the presence of at least three primary biogeographic regions with breaks around Cape Mendocino and Monterey Bay, each dominated by a different Symbiodinium muscatinei genotype. Sharp clines suggest limited gene flow between adjacent regions. Few sampling locations or individual anemones showed symbiont diversity at either organellar locus within the limits of our detection method, while sequence analysis of cloned nr18S polymerase chain reaction product suggests that nuclear pseudogenes may underlie intra-host diversity observed at that locus.