Dimethylsulfoniopropionate in giant clams (Tridacnidae)

The tridacnid clams maintain symbiotic associations with certain dinofIagel lates (termed zooxanthellae). Tridacnids are thus candidates to have high t issue concentrations of dimethylsulfoniopropionate (DMSP), a tertiary sulfo nium compound that is not synthesized by animals but is commonly produced b y dinoflagellates. This study establishes that DMSP is about an order of ma gnitude more concentrated in the Light-exposed and shaded mantle and gills of Tridacna maxima and T. squamosa than in any other known animal tissues. The DMSP concentration in the light-exposed siphonal mantle-the location of most zooxanthellae-is an inverse function of body size, paralleling an inv erse relation between apparent density of zooxanthellae (measured as pheoph ytin concentration) and body size. The shaded mantle and gills are high in DMSP despite having low densities of zooxanthellae, indicating that high DM SP concentrations occur in molluscan tissue, not just in algal cells. DMSP is almost an order of magnitude less concentrated in the adductor muscle th an in other tissues. The high DMSP concentrations found in tridacnids, by p roviding abundant substrate for formation of volatile dimethylsulfide, prob ably explain the peculiar tendency of tridacnids to rapidly develop offensi ve odors and tastes after death: a serious problem for their exploitation a s food. Tridacnids are the one group of animals in which DMSP concentration s are high enough in some tissues to be in the range capable of perturbing enzyme function at high physiological temperatures. Thus, tridacnids may re quire enzyme forms adapted to DMSP.