Mollusc secondary metabolite chemistry

The secondary metabolite chemistry of molluscs often reflects their diet since many molluscs have evolved the ability to sequester dietary metabolites for their own defense. This led to the... 

It is well established that the principal source of secondary metabolites in marine molluscs resides in the sometimes selective concentration of chemicals contained in their food. The chemical connection between molluscan predator and its algal or invertebrate diet has been confirmed as a result of many investigations of the chemistry of herbivorous [6] and carnivorous [3] molluscs and their dietary sources. However, the assumption often reported, as in a recent review [7], that marine molluscs invariably obtain their metabolites from dietary sources, should be regarded as an oversimplification. In fact, active biosynthesis of secondary metabolites has been ascertained in several cases, as documented here. 

Molluscs can be divided into two biosynthetic categories based on the chemistry they exhibit relative to their diet those that are dependent on dietary sources express chemistry that reflects their choice of diet. In some instances, molluscs have been shown to chemically modify the ingested compounds. These transformations may either enhance the deterrent nature of the metabolite or alternatively represent a detoxification mechanism examples of both are documented below. The second category of molluscs are those which have the ability to biosynthesize metabolites de novo and, hence, may sometimes express a preference for a diet lacking secondary metabolites. The expense of maintaining secondary metabolic function is balanced against the lack of dietary constraints. Molluscs that can produce their own defensive allomones are likely to have an advantage over those dependent on a dietary source of metabolites. 

The second category of nudibranchs are those which have the ability to biosynthesize metabolites de novo and, hence, may express a preference for an invertebrate diet lacking secondary metabolites.287 These molluscs show invariant chemistry independent of where they are collected.255 Experiments conducted in the mid-1980s using 14C-labeled precursors first tested the capacity of nudibranchs to undertake de novo biosynthesis. 

Cimino, G. and Sodano, G. (1993) Biosynthesis of secondary metabolites in marine molluscs, in Marine Natural Products Diversity and Biosynthesis, Topics in Current Chemistry 167 (ed. P.J. Sdieuer), Springer-Verlag, Berlin, Heidelberg, pp. 77—115. 

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