Posts Tagged 'Cnidaria'

Expression of homing endonuclease gene and insertion-like element in sea anemone mitochondrial genomes: lesson learned from Anemonia viridis


• We report complete mitochondrial genome sequences and corresponding mito-transcriptomes of the two related sea anemone species Anemonia viridis and Anemonia majano
• We describe structural features of group I introns in the NADH dehydrogenase 5 gene and the cytochrome oxidase I (COI) gene, the latter containing a homing endonuclease gene
• We provide support of that the intron homing endonuclease gene is expressed in a gene-fusion strategy involving exon 1 of the COI gene
• We show that the insertion-like element orfA is well expressed from sea anemone mitochondrial geneomes
• Long-term environmental stress due to low-seawater pH conditions results in up-regulation of COI and orfA gene expressions in Anemonia viridis


The mitochondrial genomes of sea anemones are dynamic in structure. Invasion by genetic elements, such as self-catalytic group I introns or insertion-like sequences, contribute to sea anemone mitochondrial genome expansion and complexity. By using next generation sequencing we investigated the complete mtDNAs and corresponding transcriptomes of the temperate sea anemone Anemonia viridis and its closer tropical relative Anemonia majano. Two versions of fused homing endonuclease gene (HEG) organization were observed among the Actiniidae sea anemones; in-frame gene fusion and pseudo-gene fusion. We provided support for the pseudo-gene fusion organization in Anemonia species, resulting in a repressed HEG from the COI-884 group I intron. orfA, a putative protein-coding gene with insertion-like features, was present in both Anemonia species. Interestingly, orfA and COI expression were significantly up-regulated upon long-term environmental stress corresponding to low seawater pH conditions. This study provides new insights to the dynamics of sea anemone mitochondrial genome structure and function.

Continue reading ‘Expression of homing endonuclease gene and insertion-like element in sea anemone mitochondrial genomes: lesson learned from Anemonia viridis’

Elucidating the small regulatory RNA repertoire of the sea anemone Anemonia viridis based on whole genome and small RNA sequencing

Cnidarians harbor a variety of small regulatory RNAs that include microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs), but detailed information is limited. Here, we report the identification and expression of novel miRNAs and putative piRNAs, as well as their genomic loci, in the symbiotic sea anemone Anemonia viridis. We generated a draft assembly of the A. viridis genome with putative size of 313 Mb that appeared to be composed of about 36% repeats, including known transposable elements. We detected approximately equal fractions of DNA transposons and retrotransposons. Deep sequencing of small RNA libraries constructed from A. viridis adults sampled at a natural CO2 gradient off Vulcano Island, Italy, identified 70 distinct miRNAs. Eight were homologous to previously reported miRNAs in cnidarians, whereas 62 appeared novel. Nine miRNAs were recognized as differentially expressed along the natural seawater pH gradient. We found a highly abundant and diverse population of piRNAs, with a substantial fraction showing ping–pong signatures. We identified nearly 22% putative piRNAs potentially targeting transposable elements within the A. viridis genome. The A. viridis genome appeared similar in size to that of other hexacorals with a very high divergence of transposable elements resembling that of the sea anemone genus Exaiptasia. The genome encodes and expresses a high number of small regulatory RNAs, which include novel miRNAs and piRNAs. Differentially expressed small RNAs along the seawater pH gradient indicated regulatory gene responses to environmental stressors.

Continue reading ‘Elucidating the small regulatory RNA repertoire of the sea anemone Anemonia viridis based on whole genome and small RNA sequencing’

The relationship among environmental variables, jellyfish and non-gelatinous zooplankton: a case study in the north of the Gulf of Oman

Processes underlying the temporal and spatial variations observed in the distribution of jellyfish and non-gelatinous zooplankton in the Gulf of Oman are not well understood. This information gap is clearly a major issue in controlling the harmful blooms of jellyfish and non-gelatinous zooplankton. Samples of jellyfish and non-gelatinous zooplankton were collected from six stations in Chabahar Bay and three stations in Pozm Bay within four seasons. At each station, environmental variables were also recorded from bottom and surface water. A total of 83 individuals of medusae representing four species of Scyphozoa (i.e., Cyanea nozakii, Chrysaora sp., Pelagia noctiluca, Catostylus tagi) and species of Hydrozoa (i.e., Diphyes sp., Rhacostoma sp., Aequorea spp.) were observed in the study area. A total of 70,727.25 individuals/m−3 of non-gelatinous zooplankton dominated by copepods and cladocerans were collected in nine stations within the four seasons. The results of a RELATE analysis yielded no significant association between species composition for jellyfish and non-gelatinous zooplankton. Among environmental variables, water transparency, nitrite concentration, water depth and temperature were better associated with the total variation in jellyfish species composition than with that of non-gelatinous zooplankton. Dissolved oxygen, pH, and phosphate concentration were significant environmental variables associated with the variation in the spatial and temporal distribution patterns of non-gelatinous zooplankton assemblages. Although some jellyfish species (i.e., Rhacostoma sp., Pelagia noctiluca, Catostylus tagi) occur independently of non-gelatinous zooplankton assemblages, other jellyfish (i.e., Chrysaora sp., Aequorea spp., Cyanea nozakii, Diphyes sp.) are strongly correlated with non-gelatinous zooplankton assemblages.

Continue reading ‘The relationship among environmental variables, jellyfish and non-gelatinous zooplankton: a case study in the north of the Gulf of Oman’

Effects of CO2-driven acidification of seawater on the calcification process in the calcareous hydrozoan Millepora alcicornis (Linnaeus, 1758)

Ocean acidification is expected to intensify due to increasing levels in the partial pressure of atmospheric CO2 (pCO2). This could negatively affect major calcifying reef organisms. In this study, the effects of different levels of CO2-driven acidification of seawater (control: pH 8.1; moderate: pH 7.8; intermediate: pH 7.5; and severe: pH 7.2) on the net calcification rate and activity of enzymes related to the calcification process (Ca-ATPase and carbonic anhydrase) were evaluated in the calcareous hydrozoan Millepora alcicornis. The experiment was run for 30 d using a marine mesocosm system. Net calcification ratio was significantly reduced in hydrocorals exposed to intermediate seawater acidification for 16 d and to severe seawater acidification for 16 d or 30 d, compared to animals at control conditions. However, only hydrocorals exposed to severe seawater acidification showed lower net calcification rates than those exposed to control conditions for 30 d. In accordance, the activities of enzymes involved in the calcification process markedly increased in hydrocorals exposed to reduced pH. Ca-ATPase seemed to be more sensitive to seawater acidification than carbonic anhydrase as it increased in hydrocorals exposed to intermediate and severe seawater acidification for 30 d, while carbonic anhydrase activity was only stimulated under severe seawater acidification. Therefore, our findings clearly show that the hydrocoral M. alcicornis is able to cope, to some extent, with long-term CO2-driven acidification of seawater (pH ≥ 7.5). In addition, they show that Ca-ATPase plays a key role in the maintenance of calcification rate under scenarios of moderate and intermediate levels of seawater acidification. However, the observed increase in Ca-ATPase and carbonic anhydrase activity was not enough to compensate for the effects of CO2-driven reduction in seawater pH on the net calcification rate of the hydrocoral M. alcicornis under a scenario of severe ocean acidification (pH 7.2).

Continue reading ‘Effects of CO2-driven acidification of seawater on the calcification process in the calcareous hydrozoan Millepora alcicornis (Linnaeus, 1758)’

Exposure to elevated pCO2 does not exacerbate reproductive suppression of Aurelia aurita jellyfish polyps in low oxygen environments

Eutrophication-induced hypoxia is one of the primary anthropogenic threats to coastal ecosystems. Under hypoxic conditions, a deficit of O2 and a surplus of CO2 will concurrently decrease pH, yet studies of hypoxia have seldom considered the potential interactions with elevated pCO2 (reduced pH). Previous studies on gelatinous organisms concluded that they are fairly robust to low oxygen and reduced pH conditions individually, yet the combination of stressors has only been examined for ephyrae. The goals of this study were to determine the individual and interactive effects of hypoxia and elevated pCO2 on the asexual reproduction and aerobic respiration rates of polyps of the scyphozoan Aurelia aurita during a manipulative experiment that ran for 36 d. pCO2 and pO2 were varied on a diel basis to closely mimic the diel conditions observed in the field. Exposure to low dissolved oxygen (DO) reduced asexual budding of polyps by ~50% relative to control conditions. Under hypoxic conditions, rates of respiration were elevated during an initial acclimation period (until Day 8), but respiration rates did not differ between DO levels under prolonged exposure. There was no significant effect of increased pCO2 on either asexual reproduction or aerobic respiration, suggesting that elevated pCO2 (reduced pH) did not exacerbate the negative reproductive effects of hypoxia on A. aurita polyps.

Continue reading ‘Exposure to elevated pCO2 does not exacerbate reproductive suppression of Aurelia aurita jellyfish polyps in low oxygen environments’

Climate change effects on photosynthetic symbionts in the sea anemone Anthopleura xanthogrammica

The giant green sea anemone (Anthopleura xanthogrammica) inhabits the rocky intertidal zone in California and Oregon. Two photosynthetic algal symbionts, zooxanthellae and zoochlorellae, make these anemones important primary producers in the intertidal zone. This study investigated the effects of changes in temperature and pH on anemones and their symbionts over a natural environmental gradient along the coast of California and Oregon. Zoochlorellae responded negatively to warmer temperatures and positively to more acidic conditions, while zooxanthellae responded positively to warmer temperatures and lower pH. Temperature and pH did not significantly affect chlorophyll a concentrations or anemone protein biomass. Depending on the magnitude of future changes in ocean temperatures and acidity, changes in the ranges of the two types of symbionts and increased densities of sea anemones in the rocky intertidal could be expected to occur.

Continue reading ‘Climate change effects on photosynthetic symbionts in the sea anemone Anthopleura xanthogrammica’

Ocean acidification alters zooplankton communities and increases top-down pressure of a cubozoan predator

The composition of local ecological communities is determined by the members of the regional community that are able to survive the abiotic and biotic conditions of a local ecosystem. Anthropogenic activities since the industrial revolution have increased atmospheric CO2 concentrations, which have in turn decreased ocean pH and altered carbonate ion concentrations: so called ocean acidification (OA). Single-species experiments have shown how OA can dramatically affect zooplankton development, physiology and skeletal mineralization status, potentially reducing their defensive function and altering their predatory and antipredatory behaviors. This means that increased OA may indirectly alter the biotic conditions by modifying trophic interactions. We investigated how OA affects the impact of a cubozoan predator on their zooplankton prey, predominantly Copepoda, Pleocyemata, Dendrobranchiata, and Amphipoda. Experimental conditions were set at either current (pCO2 370 μatm) or end-of-the-century OA (pCO2 1,100 μatm) scenarios, crossed in an orthogonal experimental design with the presence/absence of the cubozoan predator Carybdea rastoni. The combined effects of exposure to OA and predation by C. rastoni caused greater shifts in community structure, and greater reductions in the abundance of key taxa than would be predicted from combining the effect of each stressor in isolation. Specifically, we show that in the combined presence of OA and a cubozoan predator, populations of the most abundant member of the zooplankton community (calanoid copepods) were reduced 27% more than it would be predicted based on the effects of these stressors in isolation, suggesting that OA increases the susceptibility of plankton to predation. Our results indicate that the ecological consequences of OA may be greater than predicted from single-species experiments, and highlight the need to understand future marine global change from a community perspective.

Continue reading ‘Ocean acidification alters zooplankton communities and increases top-down pressure of a cubozoan predator’

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Ocean acidification in the IPCC AR5 WG II

OUP book