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boundaries, fo llowed by restricted gene flow among sub-basins. Regardless to the
causes of such differentiation, other marine invertebrates show a similar pattern of
genetic distribution (see Calvo et al. 2009 and references therein).

Conversely, it is not easy to identify in the SCR group the causes for the genetic
structuring occurring between cluster A, roughly corresponding to North-Western
Sardinia, and cluster B, which encompasses North-Eastern Sardinia and Corsica (Fig.
2a). This fact may be related to the presence of an inhospitable sandy shore extending
almost continuously for about l 00 km from the Asinara Island to Punta li Francesi that
may represent a hindrance to constant and conspicuous leve! of gene flow in West-East
and viceversa direction. However, ali specimens from Argentiera (North-Western
Sardinia) grouped in cluster B, representative of North-Eastern Sardinia and Corsica
(Fig. 2a, 3a). The genetic makeup of Argentiera sample may indicate that occasionai
long distance dispersa! events, in a background of reduced gene flow, may occur along
the coasts ofNorth of Sardinia and South of Corsica. Although the circulation pattern in
this area is very variable due to the complex coastal geometry, nonetheless the two
prevailing currents flow eastward and westward, respectively (Gerigny et al. 2011 ).
Nonetheless, our data do not allow to rule out the possibi lity that sample from
Argentiera is representative of a relic population and cluster B had a wider geographical
distribution in the past. Notably, the Argentiera site is the only one among those of SCR
group characterised by high cliff; additionally, the high hydrodynamic regimes
occurring in this area make almost impossible to reach it from the mainland, and
harvesting, even by sea, is hazardous. These facts may have contribute to the
conservation of traits of an ancient genetic variability.

A second, interesting results is the observed high degree of genetic structuring
within SCR group. Indeed, a clear genetic structuring in North-Western Sardinia and, at

25

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