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consisted of 100,000 iterations that followed a burn-in period of 100,000 iterations to
assess whether the results were consistent across different runs for each inferred value
of K. STRUCTURE analyses were performed on the CBSU Web Server, and graphical
displays of the results were generated using the software package DISTRUCT 1.1
(Rosenberg 2004).

In addition, we compared the results ofthe model-based clustering with a
Principal Coordinate Analysis (PCA) performed by the program GENALEX 6.3
(Peakall and Smouse 2006) on a matrix of interindividual distances via a covariance
matrix with a data standardisation method. The ordination was carried out on the entire
dataset as well as on subsets of data corresponding to the groups identified by Bayesian-
model based clustering.

Genetic structuring was also investigated by a hierarchical Analysis of
Molecular Variance (AMOVA) using the software package ARLEQUIN 3.52
(Excoffier and Lischer 20 l 0). The total variance was partitioned into covariance
components due to differences within populations, between populations within groups,
and among groups. Three different schemes of grouping were tested, two of which were
defined a priori: one scheme with two groups corresponding to SCR and SAS groups; a
second scheme with three groups, because of the further subdivision of SAS group into
Alboran Sea and Siculo-Tunisian Strait regions; the third scheme took into account the
results of model-based clustering analysis, corresponding to the highest hierarchical
genetic structuring. The significance of the fixation indices associated with the different
levels of genetic structure was assessed by a non parametric permutation test with
l 0,000 replicates (Excoffier et al. 1992).

The relationship between geographical and individuai pairwise genetic distances
were investigated using Mantel correlograms (Oden and Sokal 1986). The Mantel

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Gìan Luca Dedola: ANALISI DELLA VARIABILITÀ GENETICA DI PATELLA FéRRUGINEA, PATEL-LA UL l'SSIPONENSIS (MOLLUSCA: GASTROPODA) E PINNA
NOBILIS (MOLLUSCA: BIVALVIA): lLCONTRJBUTO DEl DATI MOLECOLARI ALLA CONSERVAZIONE DI SPECIE MINACCIATE - Tesi di douorato in Scienze
della natura e delle sue risorse · indiri7.zo BK>logi.a Ambientale, Università degli Studi di Sassarl