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Notably, while SPOOL showed numerous loci departing from HWE that are lower than
SGR, only two pairs of loci displaying LD were found in the Sardinian population.
Assuming that LD was not due to chance, the physical linkage of the loci can be ruled
out because the same pairs did not display LD in SGR. Furtherrnore, non-random
associations of Ioci may occur in populations departing from HWE (Liu et al., 2006)
and deterrnine the so-called zygotic disequilibrium (Weir, 1996). A substantial LD may
also be found in expanding populations that were initially bottlenecked as well as in
recently introduced populations (Hansson et al., 2004, and references therein). The latter
hypothesis fits with the historical data that point to a recent introduction of the
Sardinian population.
A further outcome ofthe present study was the great similarity in the level ofwithin-
population genetic diversity among the Sardinian samples from the Gulf of Olbia,
regardless ofwhether they were pooled, and also in the sample from the Lagoon of
Sacca di Goro, as evidenced by Wilcoxon rank-sum test, which was applied to the
expected heterozygosity (P= l). In fact, there was little evidence of a significant loss of
genetic variability in SPOOL and SGR under the SSM and TPM mutation models
(Table 5). Instead, they exhibited a significant deficit of heterozygozity with respect to
genetic diversity.
This finding suggests that the 'wild' population ofthe Gulf ofOibia is currently
expanding (see Ribeiro et al., 2010). This hypothesis is supported by the presence of
severa) alleles that occur at low frequencies; for example, 25 out of77 alleles (~32 %)
in SPOOL and 29 out of 69 alleles (~28 %) in SGR were found at frequencies lower
than l % (Appendix). Thus, we can conclude that the two populations are either derived
from the same source, or that the Sardinian population is derived from individuals that
were farrned in the Adriatic and released in situ.

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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