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(differentiation among groups) (Table 3). Nevertheless, the grouping matching the first
round of STRUCTURE maximised the DeT value (DeT= 0. 30 1). Among the remaining
groupings, that corresponding to SAS and SCR groups showed the highest DeT value
(Table 3).

The Mantel correlogram that included ali of the samples did not display a clear
monotonic decrease, thus suggesting a more complex spatial pattem than a simple
isolation-by-distance (IBD) or a clinal variation (Fig. 4a). The pattem was partly clinal,
with significant positive values that decreased to significant negative values in the 200
km distance class. Following an upward fluctuation, spatial autocorrelation decreased to
significantly negative values for distances from 600 up to l ,000 km, after which they
displayed a stochastic pattem. These two troughs involved many pairwise comparisons
between samples from the clusters A and B in the SCR group as well as between the
SCR group and the cluster C (the SAS group).

When the samples were divided into the three main genetic clusters identified by
the first round of STRUCTURE analyses (Fig. 2a), the autocorrelation indices showed
different spatial pattems for each of these groups (Fig. 4b, c, d). In the first distance
class (within population comparisons) clusters A and B (the SCR group) showed a
positive spatial autocorrelation (r = 0.151 and r = 0.128, respectively) greater than that
found in cluster C (the SAS group) (r = 0.047). Nevertheless in SCR group spatial
autocorrelation fell more quickly than in SAS group. In cluster A spatial autocorrelation
fell to non significant values in the second distance class (up to 15 km) whereas in
cluster B autocorrelation values were positive in the first two distance classes (up to 15
km) (Fig. 4b, c). Significantly negative autocorrelation values were observed at distance
classes that involved pairwise comparisons of specimens from different subclusters. On

21

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