Bioassays and methods used in chemical ecology studies

Natural products possess an extraordinary pharmacological effectiveness and specificity compared to artificially designed molecules because evolutionary selection has been the "nature's own high-throughput screening" process for the optimization of biologically active compounds [1,2]. In the case of marine environments, ecological pressures, including competition for space, the fouling of the surface, predation, and successfully reproducing have led to the evolution of unique secondary metabolites with various biological activities. As a result, a broad range of bioactivities has been found within the increasing number of novel secondary metabolites isolated from the under-explored marine sources [3]. This suggests that a better understanding of the ecological role of marine natural products should efficiently contribute to the selection of promising candidates in drug discovery. The purpose of this practical experience is to provide students with opportunities to examine how: (i) chemosensation is essential to food recognition, (ii) chemical stimuli can supply different information depending from the receptor organisms, and (iii) natural products contribute to chemical defense of sessile or slow-moving marine organisms in a structure- and dose-dependent manner. After a preliminary discussion introducing the students to methods used in chemical ecology studies, the work session focuses on the ability of selected metabolites, previously isolated from molluscs and/or sponges, to deter the generalist Mediterranean shrimp Palaemon elegans from feeding (as shown in figure below). This pratical experience follows a recently proposed technique to assay the effects of marine natural products on food palatability [4,5]. Control or treated pellets, prepared by the students themselves, will be presented to shrimps in series of independent replicates. The activity includes both the statistical evaluation of the results to test whether the differences between the treatments and controls are significant, and the graphic representation of the results. References 1. Paterson I., Anderson E.A., 2005. The renaissance of natural products as drug candidates. Science, 310: 451-453. 2. Clardy J., Walsh C. (2004) Lessons from natural molecules. Nature, 432: 829-837. 3. Donia M., Hamman M.T., 2003. Marine natural products and their potential applications as anti-infective agents. Lancet Infect. Dis., 3: 338-48. 4. Mollo E., Gavagnin M., Carbone M., Castelluccio F., Pozone F., Roussis V., Templado J., Ghiselin M.T., Cimino G., 2008. Factors promoting marine invasions: A chemoecological approach. PNAS, 105: 4582-4586. 5. Haber, M., Cerfeda S., Carbone M., Calado G., Gaspar H., Neves R., Maharajan V. , Cimino G., Gavagnin M., Ghiselin M.T., Mollo E., 2010. Coloration and defense in the nudibranch gastropod Hypselodoris fontandraui. Biol. Bull., 218: 181-188.