Metabolite variability in Caribbean sponges of the genus Aplysina

Abstract

tSponges of the genus Aplysina are among the most common benthic animals on reefs of the Caribbean, anddisplay a wide diversity of morphologies and colors. Tissues of these sponges lack mineralized skeletalelements, but contain a dense spongin skeleton and an elaborate series of tyrosine-derived brominatedalkaloid metabolites that function as chemical defenses against predatory fishes, but do not deter somemolluscs. Among the earliest marine natural products to be isolated and identified, these metabolitesremain the subject of intense interest for commercial applications because of their activities in vari-ous bioassays. In this study, crude organic extracts from 253 sponges from ten morphotypes amongthe species Aplysina archeri, Aplysina bathyphila, Aplysina cauliformis, Aplysina fistularis, Aplysina fulva, A.insularis, and Aplysina lacunosa were analyzed by liquid chromatography–mass spectrometry (LC–MS) tocharacterize the pattern of intra- and interspecific variabilities of the twelve major secondary metabolitespresent therein. Patterns across Aplysina species ranged from the presence of mostly a single compound,fistularin-3, in A. cauliformis, to a mixture of metabolites present in the other species. These patternsdid not support the biotransformation hypothesis for conversion of large molecular weight molecules tosmaller ones for the purpose of enhanced defense. Discriminant analyses of the metabolite data revealedstrong taxonomic patterns that support a close relationship between A. fistularis, A. fulva and A. insu-laris, while two morphotypes of A. cauliformis (lilac creeping vs. brown erect) were very distinct. Twomorphotypes of A. lacunosa, one with hard tissue consistency, the other soft and thought to belong toa separate genus (Suberea), had very similar chemical profiles. Of the twelve metabolites found amongsamples, variation in fistularin-3, dideoxyfistularin-3 and hydroxyaerothionin provided the most pre-dictive influence in decreasing order. Except for one morphotype, weak relationships were found fromwithin-morphotype analyses of metabolite concentrations as a function of geographic location (Florida,N Bahamas, S Bahamas) and depth (<10 m, 10–20 m, >20 m). Our data suggest that metabolite profiles arestrongly influenced by sponge phenotype rather than by the diverse microbiome which many Aplysinaspecies share.