Page 20 - Dedola2011

BAPS and the second round of STRUCTURE analyses resulted in the
individuals from Argentiera (North-Westem Sardinia) being grouped with the
population ofNorth-Eastem Sardinia (Punta li Francesi, Nido d'Aquila, Molara, and
Molarotto), whereas the third round of STRUCTURE analyses grouped the individuals
from Argentiera into a distinct cluster (Fig. 2a, b). In cluster C (Fig. 2a, b), two main
clusters were defined by both STRUCTURE (from the second round) and BAPS
analyses, roughly corresponding to the westemmost (Strait of Gibraltar and Alboran
Sea) and the eastemmost (Siculo-Tunisian Strait) samples from the SAS group (see
Table 1). However, these two clusters did not completely match with spatially separated
areas. In fact, the Cape Bon sample (except for one specimen) grouped with the
westemmost samples; similarly, some individuals from the Alboran Island grouped with
the eastemmost samples.

Tbe first two principal coordinates that resulted from PCA carried out on the
entire dataset accounted for 60.24% of the total variation, and identified three groups of
individuals (Fig. 3a). These groups are consistent with the highest hierarchical structure
found in the first round of STRUCTURE analyses (Fig. 2a). Furthermore, PCA
ordination based on subsets of individuals corresponding to the aforementioned groups
produced plots which tended to resemble the genetic groupings retrieved in the
subsequent rounds of STRUCTURE and BAPS analyses (Fig. 3b, c, d). According to
these results, genetic groups retrieved by Bayesian-model based clustering are unlikely
to be artefacts due to violation of the mode! assumptions (Hardy-Weinberg and linkage
equilibrium) or isolation by distance (Guillot et al. 2009).

All the three grouping schemes tested with the AMOVA (SAS and SCR;
Alboran Sea, Siculo-Tunisian Strait, and SCR; clusters A, B and C) showed a
significant genetic differentiation (P< 0.00 l) at the highest leve! of genetic structure

20

Gìan Luca Dedola: ANALISI DELLA VARIABILITÀ GENETICA DI PATELLA FéRRUGINEA, PATEL-LA ULl'SSIPONENSIS (MOLLUSCA: GASTROPODA) E PINNA
NOBILIS (MOLLUSCA: BIVALVIA): lLCONTRJBUTO DEl DATI MOLECOLARl 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