Re: Tylodina perversa - chemical defence

July 13, 2004
From: Carsten Thoms

Dear Bill,
I was very pleased to find this well-written summary of our on-going research on the sea slug forum [m9022]. Indeed it is exciting that even after more than a decade of investigations on the ecology of Aplysina sponges, these marine invertebrates are still interesting research objects and still there are many fascinating things to find out about them.

Our studies have continued since your summary in January 2003 and so I would like to update the presented data:
As you have mentioned, Tylodina perversa is a specialist predator on the sponge Aplysina aerophoba and is even able to sequester the alkaloids of its prey selectively into its own tissues (mainly into its hepatopancreas [digestive gland], its mantle and the egg ribbons). Actually the yellow colour of the opisthobranch (and its eggs) is due to the Aplysina aerophoba pigment called uranidine.

When Tylodina individuals are collected from the wild (usually by picking them from Aplysina aerophoba), besides the Aplysina aerophoba metabolites, they almost always contain aerothionin. This is surprising as this brominated alkaloid is not found in Aplysina aerophoba but is characteristic for the second Mediterranean Aplysina species, Aplysina cavernicola. To our knowledge it has not been reported before that Tylodina feeds on Aplysina cavernicola as well. What is more, the habitat of this sponge is restricted either to depths of more than 35 m or to underwater caves. Aplysina aerophoba instead grows in depths between 1 and 15 m. Choice experiments revealed that the slugs do not prefer Aplysina aerophoba when both it and Aplysina cavernicola are available together. Tylodina individuals readily feed on Aplysina cavernicola under laboratory conditions and after two weeks we found the alkaloids of this sponge in all analyzed tissues of the slugs (including the eggs).

On the other hand, in long-term feeding experiments we were able to show that even after five weeks of exclusive feeding on aerothionin-free Aplysina aerophoba, Tylodina individuals still contain almost unchanged aerothionin concentrations. Two different explanations for our findings seem conceivable to us:
•1. Tylodina in its natural environment occasionally feeds on Aplysina cavernicola, and is thereafter able to store aerothionin derived from this sponge for a very long time in its tissue.
•2. Tylodina is able to transform alkaloids derived from Aplysina aerophoba into aerothionin.

We can´t tell yet what the purpose of this selective storage of (or transformation into) aerothionin might be, as in fish feeding experiments, this metabolite revealed to be as strong a feeding deterrent as the brominated alkaloids Tylodina takes up when feeding on Aplysina aerophoba.

Concerning the “microflora” in Aplysina sponges, in collaboration with Dr. Ute Hentschel´s group at the University of Würzburg, we have started to characterize the abundant and diverse bacterial community in tissue of these invertebrates. Transplantation experiments with Aplysina cavernicola revealed an extraordinary stability of this community against changes in environmental conditions. Further we were able to show that bacteria associated with Aplysina cavernicola are members of an ocean-spanning, sponge-specific microbial community that is shared among distantly related sponges from different non-overlapping geographic regions.

For anybody who is interested in more details about our studies, please refer to our institute homepage:
www.uni-duesseldorf.de/WWW/MathNat/PharmBio/Arbeitsgruppe%20Proksch/akpp-neu.htm
or to the following publications:

• Friedrich, A. B.; Merkert, H.; Fendert, T.; Hacker, J.; Proksch, P.; Hentschel.U. (1999). Microbial diversity in the marine sponge Aplysina cavernicola (formerly Verongia cavernicola) analyzed by fluorescence in situ hybridization (FISH). Marine Bioogy, 134: 461-470
• Thoms, C.; Ebel, R.; Hentschel, U.; Proksch, P. (2003) Sequestration of dietary alkaloids by the spongivorous marine mollusc Tylodina perversa. Zeitschrift für Naturforschung, 58c: 426-432

• Thoms, C.; Horn, M.; Wagner, M.; Hentschel, U.; Proksch, P. (2003) Monitoring microbial diversity and natural product profiles of the sponge Aplysina cavernicola following transplantation. Marine Biology, 142: 685-692
•Thoms, C.; Wolff, M.; Padmakumar, K.; Ebel, R.; Proksch, P. (2004) Chemical defense of Mediterranean sponges Aplysina cavernicola and Aplysina aerophoba. Zeitschrift für Naturforschung, 59c: 113-122

For even more details please refer to my PhD thesis (sorry, this is written in German)
http://diss.ub.uni-duesseldorf.de/ebib/diss/show?dissid=859 or email me. I would be happy to answer your questions about our research.
Best wishes,
Carsten Thoms

cathoms@web.de

Thoms, C., 2004 (Jul 13) Re: Tylodina perversa - chemical defence. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/12689

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