Are there activated chemical defenses in sponges of the genus Aplysina from the Caribbean?

Abstract

The Mediterranean sponge Aplysina aerophoba has been proposed to rely on damage-induced activation of chemical defenses against pathogens and fish predators. High molecular weight brominated tyrosine derivatives have been suggested to undergo rapid, enzyme-mediated transformations into the metabolites aeroplysinin-1 and dibromocyclohexadienone following tissue damage, a process also called 'biotransformation'. These putative end-products were found to exhibit greater defensive activity compared to their precursors. Because sponges of the genus Aplysina possess similar chemical components worldwide, it has been suggested that the activation of chemical defenses is a common feature in this group. Herein, we report in situ and laboratory experiments conducted with living specimens of 2 species from the Caribbean, Aplysina insularis and A. archeri. Changes in sponge tissue secondary metabolites during time-course experiments were determined using diode-array high performance liquid chromatography coupled with mass spectrometry (LCMS) analyses of extracts of flash frozen samples. We obtained no evidence of chemical transformation after tissue damage. In short (150 s) and long (30 and 120 min) time-course experiments, conversion of the major high molecular weight brominated constituents into the low molecular weight aeroplysinin-1 or dibromocyclohexadienone was not apparent: there was neither a reduction in the concentration of putative precursor metabolites, nor an increase in end products. Past observations of transformation may be the result of differential tissue extraction efficiency, hydrolysis from insoluble precursors or the heterogeneous distribution of metabolites in sponge tissue.