Anti-predatory chemical defenses of ascidians: secondary metabolites or inorganic acids?

Abstract

Both secondary metabolites and inorganic acids have been hypothesized to protect adult ascidians from predation, raising the possibility of alternative defensive strategies in these sessile, soft-bodied, benthic invertebrates. The objective of this investigation was to determine if ascidian species from the Western Atlantic have these chemical defenses against fish predators, and if so, to determine their location within the body of the ascidian. The palatability of crude organic extracts of whole ascidians, as well as the dissected tunics, viscera, and gonads (when possible) were determined at natural volumetric concentrations using laboratory feeding assays with the bluehead wrasse, Thalassoma bifasciatum. Acidified food pellets were also assayed to determine the effect of lowered pH on predation. Sixteen of the 17 species tested had deterrent organic extracts from some region of the body (Aplidium constellatum, Aplidium stellatum, Ascidia interrupta, Ascidia nigra, Botrylloides sp., Clavellina picta, Didemnum candidum, Didemnum vanderhosti, Diplosoma listerianum, Ecteinasci-dia turbinata, Eudistoma capsulatum, Eudistoma hepaticum, Rhopalaea abdominalis, Styela plicata, Symplegma rubra, and Trididemnum solidum). The location of the deterrent secondary metabolites was isolated in the gonad in all three solitary species, raising the possibility that these defenses are passed on to eggs or larvae. Nine ascidian species sequestered acid in their tunics (A. interrupta, A. nigra, A. stellatum, D. candidum, D. vanderhosti, E. capsulatum, E. hepaticum, R. abdominalis, and T. solidum) at levels that were effective in deterring fish predation (pH V 3.0). Only one species (Botrylloides nigrum) had neither chemical defense. Results of this study indicate that there is not a clear trade-off between the presence of secondary metabolites and inorganic acid defenses in ascidians, suggesting that 0022-0981/02/$ -see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 -0 9 8 1 ( 0 2 ) 0 0 0 2 3 -0

Chemical mediation of interactions among marine organisms

“…Many species had both deterrent extracts and acidic tunics that functioned as predator defenses. 309 ' 318 Similarity has been found in the natural products chemistry of ascidian adults and larvae. 52 Little is known about chemical variation in ascidians.…”

“…26 ' 52 ' 188 Both secondary metabolites and inorganic acids have been proposed to protect adult ascidians from predation. 26 ' 307 ' 308 Pisut and Pawlik 309 tested the effectiveness of organic extracts from 17 species of tropical and warm temperate ascidians to deter feeding by Thalassoma bifasciatum.. They also assessed the effects that lowered pH (pH < 3.0), similar to levels found in the HO,, 87 88 89 tunics of some ascidians, had on fish feeding.…”

Studies on the seasonal variations in the proximate composition of ascidians from the Palk Bay, Southeast coast of India

“…Therefore, information on their growth and biochemical and energetic composition [20] are important for evaluating their nutritional value and also in modeling the flow of materials and energy within marine benthos. Moreover, low nutrient levels could make some ascidians as unattractive prey while chemical defenses (acids, heavy metals, secondary metabolites etc) may make tissues distasteful to predators [21] and inhibit the settlement of fouling microorganisms [22] . To meet out the demand, marine products are playing an excellent role as they have high protein content.…”

Antibiotic, cytotoxic and enzyme inhibitory activity of crude extracts from Brazilian marine invertebrates

“…The storage of biologically active secondary metabolites by marine invertebrates is frequently related to their ecological success, in spite of their exposition to predation, infestation by microbial pathogens, overgrowth, fouling and competition for space and nutrients (reviewed in Amsler et al, 2001;Blunt et al, 2007;Faulkner et al, 2004;Lindquist, 2002;Paul, 1992;Pawlik, 1993;Stachowicz, 2001). Marine sponges, ascidians, soft-bodied cnidaria and bryozoans are representative groups of marine invertebrates which are chemically defended against predators (for selected examples, see Aceret et al, 2001;Becerro et al, 1998;Burns et al, 2003;Chanas et al, 1996;Epifanio et al, 1999a;Epifanio et al, 1999b;Kubanek et al, 2002;Lindel et al, 2000;Lindquist, 1996;Marin et al, 1998;McClintock and Baker, 1997;O'Neal and Pawlik, 2002;Pawlik et al, 1995;Pisut and Pawlik, 2002;Stachowicz and Lindquist, 1997;Van Alstyne et al, 1994;Vervoort et al, 1998;Waddell and Pawlik, 2000), fouling (Becerro et al, 1997;Bhosale et al, 2002;Hattori et al, 2001;Henrikson and Pawlik, 1995;Kelly et al, 2003;Wahl et al, 1994), larval settlement (reviewed in Davis et al, 1989;Fusetani, 1997;Martín and Uriz, 1993;Pawlik, 1992) and solar UV radiation (Bandaranayake et...…”