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of the 45 bands scored at Tenerife none was private to this population. Furtherrnore, 31
out 45 bands were scored in more than 50% of sampling localities. Nonetheless,
homoplasy is unlikely to distort analysis restricted to intraspecific level orto groups of
closely related species, as it has been shown that most of co-migrating fragments in
these cases are identica] by descent (Nybom 2004). Similarly, we may discard the
hypothesis of a weak signal, as indeed we found a significant genetic differentiation
among populations (ct>sT = 0.271, P < 0.00 l). This pattern, suggesting population
differentiation without geographical structuring is congruent with the results obtained
with alloenzymes in continental populations ofP. ulyssiponensis (Weber and Hawkins
2005).
Another result of this work is the lack of genetic differentiation observed between
Atlantic and Mediterranean samples, across well known physical barriers to dispersal
such as the Gibraltar strait and the Oran-Almeria front (a jet ofwater between these
localities that may prevent along-shore dispersal). Interestingly, in this case the pattem
retrieved by ISSRs is congruent with mtDNA data for P. ulyssiponensis which did not
evidenced the occurrence of separated Atlantic and Mediterranean lineages (Sa Pinto et
al. 2008, Sanna et al. in press). Very similar patterns have been observed in other
species of the genus; for instance, one of the three mtDNA lineages found in P. rustica
is spread across the Atlantic and western Mediterranean, whereas the others were found
in the eastern Mediterranean (Sa Pinto et al. 2005). Though inforrnation on Patellidae
dispersa! abilities is contradictory and little is known about their pelagic larval duration
(Espinosa and Ozawa 2006), several authors suggested that P. ulyssiponensis and P.
rustica may have a high potential for dispersa] (Sella et al. 1993, Weber and Hawkins
2005). On the other hand, both ISSR and mtDNA data indicated that P. ferruginea,
which is believed to have poor dispersal capabilities, is not geographically structured

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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