Distribution of secondary metabolites in the sponge Oceanapia sp. and its ecological implications |
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Authors: | P Schupp C Eder V Paul P Proksch |
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Institution: | (1) Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Pharmazeutische Biologie, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany, DE;(2) University of Guam, UOG Marine Laboratory, Mangilao, Guam 96923,USA, GU |
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Abstract: | The Micronesian sponge Oceanapia sp. has an unusual growth form that consists of an irregular turnip-shaped base, which is buried in the substrate. One to
several fistules, which protrude through the sand, are attached to the base of the sponge. On top of each fistule is a small
fragile capitum. We examined whether this conspicuous red-colored sponge was chemically defended and if intraspecimen variation
existed in the distribution of secondary metabolites between different parts of the sponge. Furthermore we assessed the deterrent
properties of the secondary metabolites to generalist and more specialized fish predators. We also wanted to see if the optimal
defense theory holds in the case of a marine invertebrate. According to the theory, organisms evolve and allocate defenses
in a way that maximizes individual fitness, assuming that defenses are costly to the fitness of the organisms. We were able
to evaluate this hypothesis, since the different sponge parts in Oceanapia sp. were at different risk to damage by predators and had a different value in terms of fitness loss to the sponge (the capitum
probably plays a role in asexual propagation). Concentrations of crude organic extract increased from the base to the capitum
of the sponge. The major secondary metabolites kuanoniamine C and D also showed a sharp increase from the basal root to the
capitum. There was no difference in structural material or ash content between the base and the fistule of the sponge, but
fiber and protein content were significantly higher in the fistule. The methanol fraction was highly deterrent in field feeding
assays towards generalist reef fish at base concentration. It also deterred feeding by the spongivorous angelfish Pomacanthus imperator in laboratory feeding experiments at the same concentration. The field feeding assays with pure compounds showed that kuanoniamine
C and D deterred feeding by natural assemblages of reef fishes at fistule concentrations, confirming their role as defensive
agents. The intraspecimen variation of secondary metabolites in Oceanapia sp. supports the optimal defense theory by showing the highest concentrations in those parts of the sponge that are most
visible to predators and are likely to be most important for inclusive fitness.
Received: 5 May 1999 / Accepted: 16 September 1999 |
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