Abstract
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.
Highlights
The giant triton snail, Charonia tritonis (Family Ranellidae), is one of the largest gastropod snails, protected by a long, narrow shell that can measure up to half a meter in length (Hall et al 2017a)
Developmental transcriptomes of the gastropods Rapana venosa and Aplysia californica have enabled identification of genes associated with transitions between life stages (Song et al 2016; Heyland et al 2011), and as more datasets become available, comparative analysis can establish evolutionarily connectedness (De Oliveira et al 2016)
We found that 59 C. tritonis cytochrome P450 (CYP450) genes were expressed during the three development stages, with the largest number associated with steroid hormone biosynthesis (Fig. 7B)
Summary
The giant triton snail, Charonia tritonis (Family Ranellidae), is one of the largest gastropod snails, protected by a long, narrow shell that can measure up to half a meter in length (Hall et al 2017a). An adult C. tritonis eats only 1.5 COTS per week on average (Endean 1969), its mere presence alters the behaviour of COTS (Hall et al 2017a, b) This chemically mediated phenomenon has been referred to as “landscapes of fear” (Luttbeg and Kerby 2005; Preisser et al 2005; Preisser and Bolnick 2008), whereby predator presence can induce changes in prey at the physiological, phenotypic and behavioural levels It has been postulated that the “zone of fear” produced by C. tritonis has the potential to prevent COTS aggregation, leading to decreased offspring due to altered reproductive capacity (Hall et al 2017b)
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