Expression of secondary metabolites by the Mediterranean sponges Aplysina aerophoba and Aplysina cavernicola

Abstract

Aplysina aerophoba and Aplysina cavernicola are two sibling sponge species common in Mediterranean sea. External and internal morphology is almost identical in the two species. So, according to a lack of traditional taxonomic character (spicule comparison), taxonomists have longly debated if the two taxa, showing different ecological requirements but identical morphology, should be regarded as ecotypes or distinct species. Now, molecular phylogeny has brought response to this question: A. aerophoba and A. cavernicola are lately distinct species. The two species, also called bacteriosponges because of their dense community of symbiotic bacteria that can amount up to 40 % of their dry weight, can contain high amounts of secondary metabolites: brominated alkaloids derived from tyrosine (up to 13% of dry weight). As part of a program in chemical ecology where the main goal is to better understand the processes controlling the chemical diversity and its variation in marine invertebrates, (1) we finalized the methodology to quantify the major secondary metabolites produced by the two Mediterranean Aplysina species, (2) we identified chemotaxonomic markers in order to clearly discriminate the two sibling species, (3) we explored whether variation, in quality and quantity, of secondary metabolites expression occurs at different biogeographic scales, and (4) we investigated the role of microbial symbionts in bromotyrosine alkaloids biosynthesis.