Differences in the defensive performance of Iotrochota arenosa: Physical defense x Chemical defenses A. L.D. Lopes, T. S.B. Reppso, J. M. Araujo, A. G. Silva, B. G. Fleury

Abstract

Sponges can present physical and chemical anti-predation strategies with different defensive potentials, and their chemical substances are widely known for providing greater defense against predators. The genus Iotrochota Ridley,1884 is one of the examples of a genus of sponges that have several chemical substances that provide competitive advantages to species in the marine benthic environment. The present work aims to evaluate the ideal method for studying the anti-predation defenses of the sponge Iotrochota arenosa (Rützler, Maldonado, Piantoni & Riesgo, 2007) , compared to the crab Pachygrapsus transversus (Gibbes, 1850). The I. arenosa sponges were collected on the coast of Ilha do Abraão - Ilha Grande (RJ) and their extracts were tested in the laboratory, in predation bioassays against crabs with a generalist feeding habit P. transversus, collected on Boa Viagem beach, Niterói (RJ). For the bioassays, the food treatments were offered simultaneously: 1. control (lyophilized squid and agar) simultaneously with 2. chemical extracts (made separately with DCM and MeOH) 3. dry sponge. In the methodology applied, it was possible to identify whether there was a difference in defensive strategies, and which was the most efficient action used by the sponge. The differential consumption between treatments was evaluated through the percentage consumed of each food offered using the non-parametric Wilcoxon test (Statistica 7 software), considered significant when p < 0.05. In a general analysis, the two treatments, the dry sponge ( p<0.01; n=23 ) and the MeOH extract, ( p=0.01; n=23 ) were effective in defending against predation by P. transversus . However, the chemical response of the DCM extract was opposite, not only did it not present defense, it also stimulated consumption by the crab ( p=< 0.01; n=25 ). Therefore, the results indicated that the defense substances in this species are not concentrated in the most non-polar portion of the extracts tested against this predator. Methodological comparison is extremely important, so that the time and costs of the different stages of the work are minimized and the results are maximized, through the use of the most appropriate biological testing method. Therefore, further tests with different consumers are needed to more effectively evaluate the best methodology to be applied, and thus increase understanding of the defense mechanisms of this species.