Phosphoglucose Isomerase Variability in Sympatric Populations of Mediterranean Species

Genetic variability at the phosphoglucose isomerase (PGI) locus was compared in Mediterranean sympatric populations of Patella aspera, P. coerulea and P. lusitan~ca. P. aspera and P. coerulea show PG1 patterns much alike, while P. lusitanica exhibits a more anodal general zone of mobility of its PG1 allozymes. The differentiation of P. lusitanica pattern may be tentatively interpreted as the result of a selective action, which enabled this species to extend its range in the upper intertidal zone. However, all the most frequent PG1 allozymes of the Mediterranean Patella species exhibited the same degree of thermostability. Such findings suggest that, in the differentiation process of the PG1 locus in Mediterranean limpets, one or more factors other than temperature may have been involved.