Seawater carbonate chemistry and the microbiome of the octocoral Lobophytum pauciflorum

Bacteria associated with marine invertebrates are thought to have a range of important roles that benefit the host including production of compounds that may exclude pathogenic microorganisms and recycling of essential nutrients. This study characterised the microbiome of a gonochoric octocoral, Lobophytum pauciflorum, and investigated whether either sex or environmental stresses influenced the diversity of the associated microbiome through amplicon profiling of the bacterial 16S rRNA gene. Sequences affiliated to Spirochaetaceae and Endozoicimonaceae dominated the microbiome of L. pauciflorum, representing 43% and 21% of the community, respectively. Among the dominant class affiliations, no sex-specific differences were detected, though unassigned sequences were at a 2-fold higher relative abundance in samples from female individuals than from males. These potentially novel sequences contributed to observed differences between sexes as detected by a multivariate analysis at the OTU level. Exposing L. pauciflorum fragments to increased temperature (31°C), decreased pH (7.9) or both stressors simultaneously for 12 days did not significantly alter the microbial community, indicating that the soft coral microbiome is relatively resilient to short-term environmental stress

Expression of calmodulin and Acrocalcin during coral development.

<p>(A) The canonical calmodulin AmCaM is expressed at a relatively constant level during development as a ∼ 1500 bp transcript. (B) The ∼2500 bp Acrocalcin (AmAC) transcript is present at low levels at the late gastrulation stage, after which levels are relatively constant from the pear stage through to post-settlement. An early and a late pear stage were tested for AmCaM and AmAC transcripts. (C) The faint salt-and-pepper pattern visible at gastrulation reflects AmAC expression in the endoderm (b). A relatively constant expression level was observed from late gastrulation onward, sphere through post-settlement (c–g). No staining was detected in corresponding controls incubated with sense RNA probes (b′, c′, e′). Nucleic acid markers (asterisks). Pre-gastrulation (prawn chip, a). Gastrulation (donut, b). Late gastrula (sphere, c). Early planula (pear, d). Planula (e). Settlement and metamorphosis (f). Settled polyps (g). Control stages (b′, c′, e′), respectively.</p

Primary structure of the coral EF-hand proteins.

<p>(A) As in the canonical calmodulins of a wide range of other eukaryotes, the AmCaM protein contains four predicted EF-hand motifs, each of which fulfils the criteria for activity. Genbank identifiers for the sequences: <i>Acropora</i> Cluster 043479; <i>Nematostella</i> XP_00163858.1; <i>Homo</i> NP_001734.1; <i>Drosophila</i> NP_523710.1; <i>Aedes</i> XP_001662431.1; <i>Suberites</i> O97341; <i>Trichoplax</i> EDV29861.1; <i>Monosiga</i> XP_001749021.1; <i>Schizosaccharomyces</i> XP_002175972. (B) The coral Acrocalcin (AmAC) protein is a typical member of the NCS-B class, possessing an N-terminal myristoylation site (MGK, orange box), three EF-hand motifs (indicated by red boxes) and a predicted CaM-binding site (blue box). Genbank identifiers for sequences: <i>Acropora</i> Cluster 013002; <i>Nematostella1</i> XP_001639634.1; <i>Nematostella2</i> XP_001639635.1; HS (<i>Homo sapiens</i>) hippocalcin NP_002140.2; HS (<i>Homo sapiens</i>) neurocalcin NP_114430; <i>Drosophila</i> NP_788543.1; <i>Aedes</i> XP_001648788.1; <i>Amphimedon</i> XP_003386697.1; <i>Trichoplax</i> EDV23214.1; <i>Monosiga</i> EDQ90181.1.</p

The microbiome of the octocoral Lobophytum pauciflorum: minor differences between sexes and resilience to short-term stress

Bacteria associated with marine invertebrates are thought to have a range of important roles that benefit the host including production of compounds that may exclude pathogenic microorganisms and recycling of essential nutrients. This study characterised the microbiome of a gonochoric octocoral, Lobophytum pauciflorum, and investigated whether either sex or environmental stresses influenced the diversity of the associated microbiome through amplicon profiling of the bacterial 16S rRNA gene. Sequences affiliated to Spirochaetaceae and Endozoicimonaceae dominated the microbiome of L. pauciflorum, representing 43% and 21% of the community, respectively. Among the dominant class affiliations, no sex-specific differences were detected, though unassigned sequences were at a 2-fold higher relative abundance in samples from female individuals than from males. These potentially novel sequences contributed to observed differences between sexes as detected by a multivariate analysis at the OTU level. Exposing L. pauciflorum fragments to increased temperature (31°C), decreased pH (7.9) or both stressors simultaneously for 12 days did not significantly alter the microbial community, indicating that the soft coral microbiome is relatively resilient to short-term environmental stress

Data from: Larval settlement: the role of surface topography for sessile coral reef invertebrates

For sessile marine invertebrates with complex life cycles, habitat choice is directed by the larval phase. Defining which habitat-linked cues are implicated in sessile invertebrate larval settlement has largely concentrated on chemical cues which are thought to signal optimal habitat. There has been less effort establishing physical settlement cues, including the role of surface microtopography. This laboratory based study tested whether surface microtopography alone (without chemical cues) plays an important contributing role in the settlement of larvae of coral reef sessile invertebrates. We measured settlement to tiles, engineered with surface microtopography (holes) that closely matched the sizes (width) of larvae of a range of corals and sponges, in addition to surfaces with holes that were markedly larger than larvae. Larvae from two species of scleractinian corals (Acropora millepora and Ctenactis crassa) and three species of coral reef sponges (Luffariella variabilis, Carteriospongia foliascens and Ircinia sp.,) were used in experiments. L. variabilis, A. millepora and C. crassa showed markedly higher settlement to surface microtopography that closely matched their larval width. C. foliascens and Ircinia sp., showed no specificity to surface microtopography, settling just as often to microtopography as to flat surfaces. The findings of this study question the sole reliance on chemical based larval settlement cues, previously established for some coral and sponge species, and demonstrate that specific physical cues (surface complexity) can also play an important role in larval settlement of coral reef sessile invertebrates

Larval settlement: the role of surface topography for sessile coral reef invertebrates

For sessile marine invertebrates with complex life cycles, habitat choice is directed by the larval phase. Defining which habitat-linked cues are implicated in sessile invertebrate larval settlement has largely concentrated on chemical cues which are thought to signal optimal habitat. There has been less effort establishing physical settlement cues, including the role of surface microtopography. This laboratory based study tested whether surface microtopography alone (without chemical cues) plays an important contributing role in the settlement of larvae of coral reef sessile invertebrates. We measured settlement to tiles, engineered with surface microtopography (holes) that closely matched the sizes (width) of larvae of a range of corals and sponges, in addition to surfaces with holes that were markedly larger than larvae. Larvae from two species of scleractinian corals (Acropora millepora and Ctenactis crassa) and three species of coral reef sponges (Luffariella variabilis, Carteriospongia foliascens and Ircinia sp.,) were used in experiments. L. variabilis, A. millepora and C. crassa showed markedly higher settlement to surface microtopography that closely matched their larval width. C. foliascens and Ircinia sp., showed no specificity to surface microtopography, settling just as often to microtopography as to flat surfaces. The findings of this study question the sole reliance on chemical based larval settlement cues, previously established for some coral and sponge species, and demonstrate that specific physical cues (surface complexity) can also play an important role in larval settlement of coral reef sessile invertebrates

Increased radial glia quiescence, decreased reactivation upon injury and unaltered neuroblast behavior underlie decreased neurogenesis in the aging zebrafish telencephalon

The zebrafish has recently become a source of new data on the mechanisms of neural stem cell (NSC) maintenance and ongoing neurogenesis in adult brains. In this vertebrate, neurogenesis occurs at high levels in all ventricular regions of the brain, and brain injuries recover successfully, owing to the recruitment of radial glia, which function as NSCs. This new vertebrate model of adult neurogenesis is thus advancing our knowledge of the molecular cues in use for the activation of NSCs and fate of their progeny. Because the regenerative potential of somatic stem cells generally weakens with increasing age, it is important to assess the extent to which zebrafish NSC potential decreases or remains unaltered with age. We found that neurogenesis in the ventricular zone, in the olfactory bulb, and in a newly identified parenchymal zone of the telencephalon indeed declines as the fish ages and that oligodendrogenesis also declines. In the ventricular zone, the radial glial cell population remains largely unaltered morphologically but enters less frequently into the cell cycle and hence produces fewer neuroblasts. The neuroblasts themselves do not change their behavior with age and produce the same number of postmitotic neurons. Thus, decreased neurogenesis in the physiologically aging zebrafish brain is correlated with an increasing quiescence of radial glia. After injuries, radial glia in aged brains are reactivated, and the percentage of cell cycle entry is increased in the radial glia population. However, this reaction is far less pronounced than in younger animals, pointing to irreversible changes in aging zebrafish radial glia

Increased radial glia quiescence, decreased reactivation upon injury and unaltered neuroblast behavior underlie decreased neurogenesis in the aging zebrafish telencephalon

The zebrafish has recently become a source of new data on the mechanisms of neural stem cell (NSC) maintenance and ongoing neurogenesis in adult brains. In this vertebrate, neurogenesis occurs at high levels in all ventricular regions of the brain, and brain injuries recover successfully, owing to the recruitment of radial glia, which function as NSCs. This new vertebrate model of adult neurogenesis is thus advancing our knowledge of the molecular cues in use for the activation of NSCs and fate of their progeny. Because the regenerative potential of somatic stem cells generally weakens with increasing age, it is important to assess the extent to which zebrafish NSC potential decreases or remains unaltered with age. We found that neurogenesis in the ventricular zone, in the olfactory bulb, and in a newly identified parenchymal zone of the telencephalon indeed declines as the fish ages and that oligodendrogenesis also declines. In the ventricular zone, the radial glial cell population remains largely unaltered morphologically but enters less frequently into the cell cycle and hence produces fewer neuroblasts. The neuroblasts themselves do not change their behavior with age and produce the same number of postmitotic neurons. Thus, decreased neurogenesis in the physiologically aging zebrafish brain is correlated with an increasing quiescence of radial glia. After injuries, radial glia in aged brains are reactivated, and the percentage of cell cycle entry is increased in the radial glia population. However, this reaction is far less pronounced than in younger animals, pointing to irreversible changes in aging zebrafish radial glia

Comparative genomics reveals the distinct evolutionary trajectories of the robust and complex coral lineages

Despite the biological and economic significance of scleractinian reef-building corals, the lack of large molecular datasets for a representative range of species limits understanding of many aspects of their biology. Within the Scleractinia, based on molecular evidence, it is generally recognised that there are two major clades, Complexa and Robusta, but the genomic bases of significant differences between them remain unclear.The authors gratefully acknowledge the support for the Great Barrier Reef Project enabled by funding from Bioplatforms Australia through the Australian Government National Collaborative Research Infrastructure Strategy (NCRIS), Rio Tinto, a private family Foundation and the Great Barrier Reef Foundation. The work was also supported in part by of the Australian Research Council through Grant CE140100020 to DJM and to SF via the ARC Centre of Excellence for Coral Reef Studies at James Cook University