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Genetica (2011) 139:1293–1308 1305

‘‘genetic draft theory’’, which implies a reduction of that of other samples from both the SCR group and the
genetic diversity due to positive selection (Gillespie 2001). SAS group, as evidenced by the PCA ordination (Fig. 4a,
The hypothesis that selection is affecting mtDNA diversity b), which suggests the presence of a preserved population
in P. ferruginea is supported by the significant departure on the Asinara Island. However, this population appears to
from mutation-drift equilibrium, as evidenced by the neg- be isolated from the neighbouring, non protected areas of
ative values of selective neutrality tests. Although such a North-Western Sardinia (such as Coscia di Donna and Isola
signature may also reflect bottlenecks or population dei Porri), leading to potential determination of the Asinara
expansions, we are persuaded that these demographic population as a peripheral isolate (Frey 1993). More studies
processes should be ruled out because, if that was the case, on larval recruitment in this area may help to better
the ISSRs and mtDNA would have displayed similar understand whether the Asinara population also represents
genetic patterns. a ‘‘source population’’ (sensu Pulliam 1988) of genetic
variability. This variability must be preserved to assure the
Implications for conservation viability of the neighbouring populations, provided that the
harvesting of P. ferruginea is totally forbidden.
As the most endangered macroinvertebrate in the Medi- Our data from ISSRs also suggest that in the SAS the
terranean, P. ferruginea urgently requires a conservation populations from the Zembra and Sicilian islands may fit the
plan (Guerra-Garcı ´a et al. 2004). With the exception of definition of ‘‘source-sink populations’’ (sensu Pulliam
some North African P. ferruginea populations (Templado 1988), with the small populations from Pantelleria, Maret-
2001), most populations appear to be in regression and timo and Favignana derived from the Zembra island by the
below viable limits, in particular those from Sardinia and effect of the main marine currents. Thus, recovery of these
Corsica (Guerra-Garcı ´a et al. 2004). For instance, the populations could be linked to an effective plan to protect
population in the Mal di Ventre Island showed the lowest the population of Zembra. In this sense, the possible source
density among marine protected areas, 0.02 individuals per of genetic variability and connectivity between source-sink
linear meter (ind./m), ever reported for this species (Coppa, populations should be also explored by means of direct
pers. comm.); according to the literature, the average methods, such as individual genetic assignment and par-
density of P. ferruginea ranges between 0.06 and 6.86 ind./ entage analysis, to assess the hypothesis suggested here.
m (Paracuellos et al. 2003; Espinosa 2009). Low levels of The presence of populations genetically differentiated
density promote a negative feedback, since settlement of reflects the absence of effective gene flow among some
larvae is positively influenced by chemical cues of adult populations. Such populations are at high risk of extinction
conspecifics (Rivera-Ingraham et al. 2011b). To alleviate because the immigration rates are close to zero, hindering
this problem, Templado (2001) suggested the translocation the rate of population recovery, and often their population
of individuals from well-settled areas as a valuable man- sizes are low to very low. In this context, P. ferruginea
agement practice. Recent studies also suggest that patellid populations might benefit from the institution of additional
larvae can be recruited on artificial surfaces, which can protected areas and from the constitution of networks
later be successfully translocated (Rivera-Ingraham et al. among them (OSPAR 2006). The conservation networks,
2011b). However, although low-diversity mtDNA lineages which are at present considered an indispensable rowplug
are typically regarded as unimportant from a conservation to safeguard marine biodiversity, would have the twofold
viewpoint, our results based on multilocus nuclear markers aim of promoting (1) an effective interaction to support non
suggest that great caution should be exercised when protected areas and (2) a synergy among protected areas to
translocations are planned due to the genetic heterogeneity achieve conservation objectives (Ardron 2008), among
observed even on a very small local scale. which preservation of the genetic variability and gene flow
In this context, the ISSR genetic differentiation found should be prominent (OSPAR 2006). Such initiatives
within the SCR group may be of crucial importance to would be of great interest, especially for those populations
conservation efforts. For instance, in North-Western which may be potentially genetically connected.
Sardinia, particular attention should be paid to the Argen-
tiera population, in which individuals show the genetic Acknowledgments This research was financially supported by the
European Community INTERREG III (2000–2004), the Centro di
makeup of samples from North-Eastern Sardinia and Cor-
Eccellenza of the University of Sassari (2000–2004), the Provincia di
sica (cluster B) (Fig. 3a, b), and the population from the Olbia-Tempio (2010), and the Regione Autonoma della Sardegna—
protected area of Asinara Island, where the three subsam- PO Sardegna FSE 2007–2013—L.R. 7/2007’’Promozione della ric-
ples analysed (Cala Sant’Andrea, Punta Sabina, and Pedra erca scientifica e dell’innovazione tecnologica in Sardegna’’. Part of
the genetic analysis was carried out using the resources of the
Bianca) (Table 1; Fig. 1) show a high degree of identity,
Computational Biology Service Unit at Cornell University. We wish
suggesting an efficient gene flow within the island. Fur- to gratefully thank Dr. Fabio Scarpa (University of Sassari) for his
thermore, the scattering of its individuals is greater than help in checking the MS, and Dr. Stefania Coppa (CNR—Consiglio

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