A Glycoprotein in Shells of Conspecifics Induces Larval Settlement of the Pacific Oyster Crassostrea gigas

Tilmann Harder,Hebert Ely Vasquez,Kyotaro Hashimoto,Cyril Glenn Satuito,Chisato Chris Imai,Asami Yoshida,Hitoshi Kitamura,Kenji Hara

doi:10.1371/journal.pone.0082358

Abstract

Settlement of larvae of Crassostrea gigas on shell chips (SC) prepared from shells of 11 different species of mollusks was investigated. Furthermore, the settlement inducing compound in the shell of C. gigas was extracted and subjected to various treatments to characterize the chemical cue. C. gigas larvae settled on SC of all species tested except on Patinopecten yessoensis and Atrina pinnata. In SC of species that induced C. gigas larvae to settle, settlement was proportionate to the amount of SC supplied to the larvae. When compared to C. gigas SC, all species except Crassostrea nippona showed lower settlement inducing activities, suggesting that the cue may be more abundant or in a more available form to the larvae in shells of conspecific and C. nippona than in other species. The settlement inducing activity of C. gigas SC remained intact after antibiotic treatment. Extraction of C. gigas SC with diethyl ether (Et2O-ex), ethanol (EtOH-ex), and water (Aq-ex) did not induce larval settlement of C. gigas larvae. However, extraction of C. gigas SC with 2N of hydrochloric acid (HCl-ex) induced larval settlement that was at the same level as the SC. The settlement inducing compound in the HCl-ex was stable at 100°C but was destroyed or degraded after pepsin, trypsin, PNGase F and trifluoromethanesulfonic acid treatments. This chemical cue eluted between the molecular mass range of 45 and 150 kDa after gel filtration and revealed a major band at 55 kDa on the SDS-PAGE gel after staining with Stains-all. Thus, a 55 kDa glycoprotein component in the organic matrix of C. gigas shells is hypothesized to be the chemical basis of larval settlement on conspecifics.

Highlights

In the life cycle of most marine invertebrates, settlement marks the transition from planktonic larval to sessile adult phase [1]
Settlement inducing activities of the different shell chips (SC) were assessed with Tukey HSD test for multiple comparisons after all data were fitted in the quasi-binomial model
We demonstrated that larvae of the Pacific oyster C. gigas differentially settle on shells of different species of mollusks (Fig. 2), albeit in higher numbers on conspecific shells and those of C. nippona (Fig. 3)

Summary

Introduction

In the life cycle of most marine invertebrates, settlement marks the transition from planktonic larval to sessile adult phase [1]. More evidence suggest that larval settlement is a dynamic process where larvae actively respond to a wide range of variables or cues that may provide information to secure a site appropriate for its post-settlement growth and survival [4]. These cues may come from microbial or bacterial biofilms, prey or predator, conspecifics and macroalgal hosts [5,6]. The prevalence of gregariousness in sessile marine communities suggests that benefits outweigh the disadvantages

Methods

Results

Conclusion