Ontogeny of a symbiont-produced chemical defense in Bugula neritina (Bryozoa)

The larvae of the arborescent bryozoan Bugula neritina are chemically defended against predators by unpalatable secondary metabolites called bryostatins. Bryostatins, polyketide- derived secondary compounds, are produced by the bacterial symbiont 'Candidatus Endobugula sertula', which is present throughout all life stages of B. neritina. Crude extracts of larval and all juve- nile stages of B. neritina significantly reduced pinfish feeding (p < 0.003). Extract unpalatability is due to high bryostatin concentrations. As B. neritina increases in age after larval settlement and metamor- phosis, palatability increases as bryostatin concentrations decrease precipitously. Extracts of brood- ing portions of adult colonies reduced pinfish feeding by a significant 54% (p = 0.008), whereas ex- tracts of non-brooding portions of the same colonies resulted in a non-significant 20% decline in feeding (p = 0.125). Our data suggest that the different life stages of B. neritina employ alternate de- fensive strategies. The mobile, short-lived larvae and early-stage juveniles are defended from preda- tors by having deterrent levels of bryostatins; in contrast, the older juveniles and adults, which are clonal and relatively long-lived, may be defended largely by high levels of structural material (i.e. chitin and carbonate). Predation pressure on the vulnerable larval stage of B. neritina appears in part to have driven selection for the development and maintenance of the symbiotic relationship between B. neritina and Ca. Endobugula sertula whereby the larvae are chemically defended by symbiont- produced bryostatins.