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noncoding DNA sequences, which evolve faster and are less constrained by selection
than mtDNA genes (e.g., De Aranzamendi et al. 2009). lndeed, mtDNA may be affected
by natura] selection (Ballard and Whitlock 2004), which may drastically reduce the
number of haplotypes. In particular, Bazin et al. (2006) suggested that the mtDNA
variation in invertebrates is consistent with the 'genetic draft theory', which implies a
reduction of genetic diversity due to positive selection (Gillespie 200 l). Patella
ferruginea mainly occurs in the rocky intertidal zone exposed to wave action, where
challenging ecologica! conditions may enhance the processes of rapid selection for a
restricted number of haplotypes. The hypothesis that selection is affecting mtDNA
diversity in P. ferruginea is supported by the significant departure from mutation-drift
equilibrium, as evidenced by the negative values of selective neutrality tests. Although
such a signature may also reflect bottlenecks or population expansions, we are
persuaded that these demographic processes should be ruled out because, if that were
the case, the ISSRs and mtDNA would have displayed simi lar genetic pattems.
Whatever the reason that led to the observed lack of mtDNA genetic variability, our
study evidenced the scarce contribute of this molecule to infer on phylogeographic
pattems ofP. ferruginea.

Implications for conservation

As the most endangered macroinvertebrate in the Mediterranean, P. ferruginea urgently
requires a conservation plan (Guerra-Garcia et al. 2004). With the exception of some
North African P. ferruginea populations (Templado 200 l), most others appear to be in
clear regression and below viable limits (Templado and Moreno 1997). To alleviate this
problem, Templado (200 l) suggested the translocation of individuals from well-settled

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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