Page 49 - Dedola2011

Introduction
Bivalves (Mollusca: Bivalvia) represent one of the most common organisms in

marine and freshwater environments (Morton, 1996), whose free-swimming pelagic
larva! phase (veliger) may be involved in the high potential for dispersal oftheir species
(Gosling, 2003). Even if different environmental parameters among marine basins may
shape dispersa! patterns influencing biodiversity (Bianchi 2007), marine habitats, when
opposing a low leve! of physical barriers to genetic exchange, could play an important
role in the dispersion even for bivalve sessile species with a benthonic life cycle. In fact,
high rates of gene flow mediated by elevated levels of dispersa! could affect
evolutionary genetic processes independently from geographical factors. In addition the
efficiency of species' potential for dispersa! and recruitment is strongly involved in
capability of ocean currents to transport larvae (Domeier, 2004; Peharda and Vilibié,
2008). Therefore, the knowledge of potential for dispersa! and genetic settlement of
species along their range of distribution, could be helpful in depicting the population
dynamics which contributed to set their biogeographic background tracing signatures in
the spatial distribution of molecular variation (Avise et al. 1987).

Under a molecular perspective, different authors tried to shed some light on the
early origin of the class of bivalves. However, conflicting results produced a confused
perspective on this topic, probably as consequence of the bivalves rapid genome
evolution (Huvet et al. 2000; Launey and Hedgecock 2001, Knudsen et al. 2006; Piazzi
and Passamonti 2010). Only recently Piazzi and Passamonti (2010), using four
mitochondrial markers, evidenced that ali main deep events in bivalves radiation took
piace in a relatively short 70 Myr time during late Cambrianlearly Ordovician. Among
the class of Bivalvia, mussels (Mytilus, Pinna), scallops (Pecten, Chlamys), oysters

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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