Intra- and interspecific variation in electrophoretic profiles of Tethya spp.: an integration to morfological classification system

Here we described an original protocol based on the comparison of the electrophoretic protein profiles of crude extracts from three different population of sponges of genus Tethya, i.e. Tethya aurantium (Ta), T. citrina (Tc) and T. meloni (Tm), collected in three Mediterranean sites located along the coast of Apulia (Italy) This protocol allows to support the taxonomic classification for the discrimination between sponge species that are hard to identify since they are phylogenetically close and present similar morphological features. The computerized images of Native-PAGE gels were analysed using the freeware 1D gel electrophoresis image analysis software GelAnalyzer (http://www.gelanalyzer.com) and for each crude extract the protein bands clearly defined were taken into consideration. The polymorphic bands were scored visually as either present (1) or absent (0). These data were used for the calculation of a similarity coefficient using the Jaccard coefficient similarity matrices. The data sets were analysed using DendroUPGMA, a dendrogram construction utility (http://gesnomes.urv.es/UPGMA/). The resulted dendogram showed that all the sampled specimens of T. meloni could be grouped together in an isolate cluster. On the other hand, this methodology seemed to discriminate in a less accurate way between samples of T. citrina and T. aurantium based on the similarity of their protein profiles. In particular, T. aurantium specimens sampled in “Palese” resulted to be more similar to T. citrina samples collected in “Mar Piccolo” than to the conspecific organism collected in Manfredonia. Results obtained suggest that this method is highly reproducible, fast and inexpensive therefore it can be used to complement traditional methods of taxonomic classification, especially where the morphological analyses present uncertain or ambiguous results. Moreover, given the simplicity and relatively low cost of the proposed technique, it could be extended to other classes of marine organisms.