Studio citogenetico della famiglia Muraenidae (Anguilliformes: Actinopterygii) mediante tecniche di citogenetica classica e molecolare

Moray eels (Actinopterygii, Anguilliformes, Muraenidae) are teleosts widespread in tropical and temperate seas and among the most common predators of the coral reef. Nevetherless, they are too little studied due to their hidden and nocturnal habits; furthermore, they are not important commercially, and in Asian countries are involved in ciguatera poisoning in humans. Beside the ciguatera fish poisoning, most studies concern the taxonomy, mainly based on morphology and body colour pattern; however the classification of species and genera is still controversial. Comparative cytogenetic, allowing the study of karyotype evolution among species and genera, could contribute to shed light on taxomomic and phylogenetic incertainties on Muraenidae family. Till now, less of 10% have been karyologically analysed and a very few number of species have been studied by molecular and comparative cytogenetics. Whitin a karyological study on anguillifom teleosts, and in particular on morays, in this PhD reseach, a comparative cytogenetic analysis of six Indo-Pacific moray eels from three different genera (Gymnothorax fimbriatus, Gymnothorax flavimarginatus, Gymnothorax javanicus, Gymnothorax undulatus, Echidna nebulosa and Gymnomuraena zebra), was carried out, using Wright’s staining and C-banding in order to investigate the chromosomal differentiation in the family Muraenidae. Four species displayed a diploid chromosome number 2n=42, which is common among the Muraenidae. Two other species were characterized by different chromosome numbers (2n=40 and 2n=36). For most species, a large amount of constitutive heterochromatin was detected in the chromosomes, with species-specific C-banding patterns that enabled pairing of the homologous chromosomes. In all species, the major ribosomal genes were localized in the guanine-cytosine-rich region of one chromosome pair, with different chromosomal locations. The (TTAGGG)n telomeric sequences were mapped onto chromosomal ends in all the muraenids studied. Since the minor ribosomal family have been never studied in any moray species, in this study the 5S rDNA have been mapped, beside three Indopacific moray, in the Mediterranean species G. unicolor e Muraena helena. Almost all species displayed multiple cluster of 5S genes with both different as well as conserved localizations among species. The comparison of the results derived from this study with those available in the literature confirms a substantial conservation of the diploid chromosome number in the Muraenidae and supports the hypothesis that rearrangements have occurred that have diversified their karyotypes. Furthermore, the finding of two species with different diploid chromosome numbers suggests that additional chromosomal rearrangements, such as Robertsonian fusions, have occurred in the karyotype evolution of the Muraenidae.