Exploring molecular variation in the cosmopolitan Caprella penantis (Crustacea: Amphipoda): results from RAPD analysis

Eight populations of Caprella penantis, three of Caprella dilatata and two of Caprella andreae, collected from different sites all over the world, were selected for genetic study. Thirteen primers were tested, and the phenogram, based on the similarity coefficient of Nei & Li and the UPGMA method, separated clearly C. dilatata and C. andreae from the populations of C. penantis, supporting the validity of these three species, traditionally considered altogether under the old 'acutifrons' complex. Populations of C. penantis (including, at least, forms simulatrix, testudo and lusitanica) from Spain, Portugal, Morocco, Japan and Brazil were clustered together in the RAPD analysis, indicating that, probably, all the specimens of C. penantis could belong to the same species, in spite of morphological variations in the pleura, gills, robustness and presence/absence of proximal projection in adult male gnathopod 2 propodus. The only population which showed genetic differentiation within the C. penantis complex was the form gibbosa from Coquimbo, Chile. Future analysis based on different molecular approaches (mtDNA, 18S rRNA, ISSR) and additional material from other world areas, should be conducted to confirm these results.