VARIABILITÀ GENETICA E MORFOLOGICA NEL FRAGOLINO, PAGELLUS ERYTHRINUS

ABSTRACT In the last decades, recent molecular approaches have lead to fundamental changes in our understanding of marine population ecology. The classical notion that marine environments tend to be demographically ‘open’, with high connectivity among populations of infinite size and generally characterized by low genetic differentiation (Hauser and Carvalho, 2008) is quite abandoned. In fact, recent genetic studies have challenged such traditional view, by demonstrating genetic structuring in marine fish species, even on a limited spatial scale (Knutsen et al., 2003; Jørgensen et al., 2005; Knutsen et al., 2007). Moreover, it became clear that the degree of dispersion and the extent of gene flow among marine populations are strongly influenced by oceanographic discontinuities (transition areas that could determine phylogeographic discontinuities) suggesting that the picture is much more complex than previously assumed (Schunter et al., 2011). In this context, we investigated the distribution of genetic and morphological variability of Pagellus erythrinus (common pandora), one of the main target species in Mediterranean commercial fisheries and whose knowledge on biological features is still limited. The aim of this thesis was to investigate the degree of genetic structure of common pandora, necessary for a correct management of this resource and, to increase knowledge of the genetic variability distribution patterns in the Sparidae family and, more generally, in Mediterranean demersal species. The morphological analysis aims to investigate the degree of morphological differentiationon a geographical basis, and its possible concordance/correlation with genetic variability. Specimens were collected from 16 localities along the Italian (13 sites) and the Tunisian coasts (2 sites), in the central Mediterranean Sea, and from one location in the Atlantic Ocean, along the southern coast of Portugal. Genetic analyses were carried out using three different molecular markers: two mitochondrial DNA markers, control region (CR, sequence analysis) and cytochrome b (Cyt b RFLP analysis) and a nuclear one, microsatellites (10 loci). We identified three different mitochondrial lineageseach including individuals from almost every sampling sites, without a geographic pattern. Nevertheless, different, and statistically significant, frequency distribution was found for two of the these lineages between the Mediterranean Sea and the Atlantic Ocean. The presence of these long-diverged lineages, that now can be found in sympatry, is attributable to a period of isolation followed by secondary contact. These events, likely due to climatic fluctuations of the Pleistocene, left decipherable genetic footprints on phylogeographic and demographic facets of common pandora history. Microsatellites showed that present-day dynamics produces a weak but significant genetic structure (Fst= 0.006, p < 0.05) among the examined localities. One Atlantic and four Mediterranean subpopulations were identified, which might be explained by the major oceanographic discontinuities and local currents described in the investigated area. A certain degree of differentiation was observed for some localities within the Mediterranean Sea (North Elba and along the Tunisian coasts) for which phylogeographic breaks have not been reported so far. Further studies will be necessary to better understand dispersal components in relation both to local oceanographic conditions and adults mobility . Data obtained with the two types of molecular markers allow us to assert that the species in the past has been affected by processes of isolation, and, consequently, genetic divergence of populations followed bysecondary contact, Under present day conditions, populations are characterized by high connectivity and dispersal is limited only in some restricted areas. Morphological analysis was carried out by a geometric morphometrics approach, through the detection of 20 landmarks. The analysis revealed morphological variations in size and shape components, both between sexes and sites. The variability in size could be due to different local environmental features and to the hermaphroditism of the species. Differences in shape could be related to a slight sexual dimorphism. Statistical tests revealed absence of correlation between morphological and genetic patterns indicating that phenotypic plasticity and adaptive divergence/convergence are potential mechanisms underlying morphological differences detected among P. erythrinus.