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4. DISCUSSION AND CONCLUSION
This study demonstrates a high degree of genetic variability of R. philippinarum at six
microsatellite loci. At each locus, the size range of the alle!es, the number of alleles, and
the number of effective alleles were higher than those reported by Yasuda et al. (2007).
The observed and expected heterozygosity displayed values that were comparable in
magnitude to those reported by Yasuda et al. (2007) and Chiesa et al. (20 11). In
particular, although the values of expected heterozygosity were lower in our samples at
Asari24, Asari43 and Asari55 (Table 4), the differences in our values and in those
detected by Yasuda et al. (2007) were not significant (Wilcoxon rank-sum test, P=
0.394). Two out of six loci, Asari24 (in SGR) and Asari55 (in SPOOL and SGR),
showed an overall deficit ofheterozygosity, a phenomenon that is comrnon in other
bivalves (i.e. Hare et al., 1996; Raymond et al., 1997; Vargas et al., 2008).
Chiesa et al. (2011) found moderate levels of genetic differentiation in microsatellites
among clam populations from the North Adriatic sea, hypothesizing that such genetic
differentiation may be the result of multiple introductions from different gene pools. In
contrast, we detected a lack of genetic substructuring within the Gulf of Olbia (Tables 2
and 3). Our results are suggestive of i) a single introduction event or ii) multiple
introductions either from the same source population or from genetically
undifferentiated populations.
The results provided by model-based clustering for the whole dataset (Table 2) also
identified a common origin for the Sardinian and Adriatic samples. Although private
alleles were found in SPOOL, the two populations share the same gene pool, likely
because not enough time has elapsed to achieve a significant amount of divergence
(Hutchison and Templeton 1999).

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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