Implications for muricid (sub)species
Molecular characterization of the corallivorous muricids of Koh Tao shows that all species fall neatly within the expected existing groups of widely sampled muricid species. The two marker dataset produced a satisfactory tree with strong branch support. For Drupella rugosa, variation in shell morphology was noted. Nevertheless, no molecular basis was found to distinguish the variation, as was also found when Johnson and Cumming (1995) tested for D. fragum and D. rugosa hybrids. Moreover, no prey-related cryptic speciation seems to occur in D. rugosa, although data on this subject is preliminary and specimens from different prey should be more thoroughly sampled. Host-associated differentiation is already known from a selection of Caribbean and Indo-Pacific coralliophillines (Johnston et al., 2012; Simmonds et al., 2012), although this may not be the case and otherwise harder to prove for Drupella, owing to their cryptic and adaptive prey choice.
The sampled D. margariticola were part of the ‘Continental’ clade in which corallivory was already known to occur (Claremont et al., 2011a). The theory that all snails belonging to this clade could potentially feed on coral tissue is supported by this study and possibly far more widespread than currently documented. Coral consumption by Morula spinosa has formerly been documented for Japan (Yokochi, 2004) and now for Thailand. The coral feeding individuals do not differ genetically from conspecifics and thus the same applies, implying that this widespread species may feed on corals in other locations. Moreover, more muricid taxa could be able to opportunistically feed on corals than is currently known, as it has only recently been discovered for M. spinosa (Yokochi, 2004) and Ergalatax junionae (Saledhoust et al., 2011).