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accounting for 3.90% oftotal variation (<l>cT = 0.039, P< 0.01). Interestingly, a furth er

partitioning of the two Mediterranean basins into smaller groups increased the portion
of total variance explained by differences among groups (Table 4). Among these
groupings, the fixation index was maximised when populations were grouped according
to the following scheme: Alboran sea, Balearic sea and Gulf of Lions (group 1);
Sardinian-Corsican region and western Tyrrhenian sea (BDF, IFO and CGA); south-
eastem Sicily (MRS, TOR, PSE, APE and PLM); Lampedusa island; Cyprus. Genetic
differentiation among these groups accounted for about 6% of total variation (<l>eT =
0.059, p < 0.001).

Discussion
Studies conducted so far analysed the pattern of genetic variation among Macaronesian
and continental populations of Patella ulyssiponensis. The congruent patterns found
with different marker systems such as alloenzymes (Weber and Hawkins 2005) and
mtDNA (Sa Pinto et al. 2008, Sanna et al. in press) evidenced l) a clear genetic
differentiation between Macaronesian and continental populations and 2) lack of spatial
genetic structure throughout continental Europe. Conversely, results obtained with ISSR
markers, did not support the genetic differentiation between samples from Tenerife
(Macaronesia) and those from Europe (Fig. 3, Table 4). This result must be interpreted
with caution as samples from Macaronesia were collected at a single point location; we
cannot rule out that a more thorough sampling of Macaronesia would give a different
picture. Assuming this pattern is true the lack of genetic differentiation between
Tenerife and continental samples may be due to a high degree ofhomoplasy (i.e. co-
migrating bands are identica} by state rather than by descent) orto a scant signa! of
differentiation in ISSR banding pattems. Both hypotheses cannot be excluded a priori;

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Gìan Luca Dedola: ANALISI DELLA VARIABILITÀ GENETICA DI PATELLA FéRRUGINEA, PATEL.LA ULl'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