Development and Interrogation of a Transcriptomic Resource for the Giant Triton Snail (Charonia tritonis).

Gastropod molluscs are among the most abundant species that inhabit coral reef ecosystems. Many are specialist predators, along with the giant triton snail Charonia tritonis (Linnaeus, 1758) whose diet consists of Acanthaster planci (crown-of-thorns starfish), a corallivore known to consume enormous quantities of reef-building coral. C. tritonis are considered vulnerable due to overexploitation, and a decline in their populations is believed to have contributed to recurring A. planci population outbreaks. Aquaculture is considered one approach that could help restore natural populations of C. tritonis and mitigate coral loss; however, numerous questions remain unanswered regarding their life cycle, including the molecular factors that regulate their reproduction and development. In this study, we have established a reference C. tritonis transcriptome derived from developmental stages (embryo and veliger) and adult tissues. This was used to identify genes associated with cell signalling, such as neuropeptides and G protein-coupled receptors (GPCRs), involved in endocrine and olfactory signalling. A comparison of developmental stages showed that several neuropeptide precursors are exclusively expressed in post-hatch veligers and functional analysis found that FFamide stimulated a significant (20.3%) increase in larval heart rate. GPCRs unique to veligers, and a diversity of rhodopsin-like GPCRs located within adult cephalic tentacles, all represent candidate olfactory receptors. In addition, the cytochrome P450 superfamily, which participates in the biosynthesis and degradation of steroid hormones and lipids, was also found to be expanded with at least 91 genes annotated, mostly in gill tissue. These findings further progress our understanding of C. tritonis with possible application in developing aquaculture methods.

Putative chemosensory receptors are differentially expressed in the sensory organs of male and female crown-of-thorns starfish, Acanthaster planci.

BACKGROUND: Chemosensation is a critical signalling process for all organisms and is achieved through the interaction between chemosensory receptors and their ligands. The Crown-of-thorns starfish, Acanthaster planci species complex (COTS), is a predator of coral polyps and Acanthaster cf. solaris is currently considered to be one of the main drivers of coral loss on the Great Barrier Reef in Queensland, Australia. RESULTS: This study reveals the presence of putative variant Ionotropic Receptors (IRs) which are differentially expressed in the olfactory organs of COTS. Several other types of G protein-coupled receptors such as adrenergic, metabotropic glutamate, cholecystokinin, trace-amine associated, GRL101 and GPCR52 receptors have also been identified. Several receptors display male-biased expression within the sensory tentacles, indicating possible reproductive significance. CONCLUSIONS: Many of the receptors identified in this study may have a role in reproduction and are therefore key targets for further investigation. Based on their differential expression within the olfactory organs and presence in multiple tissues, it is possible that several of these receptor types have expanded within the Echinoderm lineage. Many are likely to be species-specific with novel ligand-binding affinity and a diverse range of functions. This study is the first to describe the presence of variant Ionotropic Glutamate Receptors in any Echinoderm, and is only the second study to investigate chemosensory receptors in any starfish or marine pest. These results represent a significant step forward in understanding the chemosensory abilities of COTS.

Chemical imaging of a Symbiodinium sp. cell using synchrotron infrared microspectroscopy: a feasibility study.

The symbiotic relationship between corals and Symbiodinium spp. is the key to the success and survival of coral reef ecosystems the world over. Nutrient exchange and chemical communication between the two partners provides the foundation of this key relationship, yet we are far from a complete understanding of these processes. This is due, in part, to the difficulties associated with studying an intracellular symbiosis at the small spatial scales required to elucidate metabolic interactions between the two partners. This feasibility study, which accompanied a more extensive investigation of fixed Symbiodinium cells (data unpublished), examines the potential of using synchrotron radiation infrared microspectroscopy (SR-IRM) for exploring metabolite localisation within a single Symbiodinium cell. In doing so, three chemically distinct subcellular regions of a single Symbiodinium cell were established and correlated to cellular function based on assignment of diagnostic chemical classes.

Multiomics analysis of the giant triton snail salivary gland, a crown-of-thorns starfish predator.

The giant triton snail (Charonia tritonis) is one of the few natural predators of the adult Crown-of-Thorns starfish (COTS), a corallivore that has been damaging to many reefs in the Indo-Pacific. Charonia species have large salivary glands (SGs) that are suspected to produce either a venom and/or sulphuric acid which can immobilize their prey and neutralize the intrinsic toxic properties of COTS. To date, there is little information on the types of toxins produced by tritons. In this paper, the predatory behaviour of the C. tritonis is described. Then, the C. tritonis SG, which itself is made up of an anterior lobe (AL) and posterior lobe (PL), was analyzed using an integrated transcriptomics and proteomics approach, to identify putative toxin- and feeding-related proteins. A de novo transcriptome database and in silico protein analysis predicts that ~3800 proteins have features consistent with being secreted. A gland-specific proteomics analysis confirmed the presence of numerous SG-AL and SG-PL proteins, including those with similarity to cysteine-rich venom proteins. Sulfuric acid biosynthesis enzymes were identified, specific to the SG-PL. Our analysis of the C. tritonis SG (AL and PL) has provided a deeper insight into the biomolecular toolkit used for predation and feeding by C. tritonis.

Neuropeptides encoded within a neural transcriptome of the giant triton snail Charonia tritonis, a Crown-of-Thorns Starfish predator.

Neuropeptides represent a diverse class of signaling molecules originating from neural tissues. These chemical modulators orchestrate complex physiological events including those associated with growth and reproduction. De novo transcriptome sequencing of a cerebral ganglion library of the endangered giant triton snail (Charonia tritonis) was undertaken in an effort to identify key neuropeptides that control or influence its physiology. The giant triton snail is considered a primary predator of the corallivore Acanthaster planci (Crown-of-Thorns Starfish) that is responsible for a significant loss in coral cover on reefs in the Indo-Pacific. The transcriptome library was assembled into contigs, and then bioinformatic analysis was used to identify a repertoire of 38 giant triton snail neuropeptide precursor genes, and various isoforms, that encode conserved molluscan neuropeptides. C. tritonis neuropeptides show overall precursor organisation consistent with those of other molluscs. These include those neuropeptides associated with mollusc reproduction such as the APGWamide, buccalin, conopressin, gonadotropin-releasing hormone (GnRH), NKY and egg-laying hormone. These data provide a foundation for further studies targeted towards the functional characterisation of neuropeptides to further understand aspects of the biology of the giant triton snail, such as elucidating its reproductive neuroendocrine pathway to allow the development of knowledge based captive breeding programs.

Chemical mediation of coral larval settlement by crustose coralline algae.

The majority of marine invertebrates produce dispersive larvae which, in order to complete their life cycles, must attach and metamorphose into benthic forms. This process, collectively referred to as settlement, is often guided by habitat-specific cues. While the sources of such cues are well known, the links between their biological activity, chemical identity, presence and quantification in situ are largely missing. Previous work on coral larval settlement in vitro has shown widespread induction by crustose coralline algae (CCA) and in particular their associated bacteria. However, we found that bacterial biofilms on CCA did not initiate ecologically realistic settlement responses in larvae of 11 hard coral species from Australia, Guam, Singapore and Japan. We instead found that algal chemical cues induce identical behavioral responses of larvae as per live CCA. We identified two classes of CCA cell wall-associated compounds--glycoglycerolipids and polysaccharides--as the main constituents of settlement inducing fractions. These algae-derived fractions induce settlement and metamorphosis at equivalent concentrations as present in CCA, both in small scale laboratory assays and under flow-through conditions, suggesting their ability to act in an ecologically relevant fashion to steer larval settlement of corals. Both compound classes were readily detected in natural samples.

Temperature and spatiotemporal variability of Salicylihalamide A in the sponge Haliclona sp.

The production of salicylihalamide A by the marine sponge Haliclona sp. was investigated. Samples of the two morphologies (green and brown) were collected from four locations covering approximately 1,200 km of coastline. Temporal variation between winter and summer was also examined at Bremer Bay. Chemical profiling by using liquid chromatography coupled with ultra violet detection and mass spectrometry showed that salicylihalamide A was produced only by the green morphology. Salicylihalamide A concentration was significantly correlated to water temperature but not to the size or depth of the sponge. Salicylihalamide A concentration was found to differ significantly among locations (Bremer Bay 13.5 microg g(-1), Hamelin Bay 11 microg g(-1), Rottnest Island 9.9 microg g(-1), and Jurien Bay 8.5 microg g(-1)) partially accounted for by the influence of water temperature. A difference between seasons was also observed in Bremer Bay (summer concentration of 13.5 microg g(-1) vs. winter concentration of 8.2 microg g(-1)). Environmental and physiological factors appear to be important in the production of salicylihalamide A by the green morphology. Additionally, the brown morphology does not produce salicylihalamide A, thus adding to the evidence that this morphology may be a different species.