Genetic variation, systematics and distribution of the venerid clamChamelea gallina

Abstract

Two morphotypes of the venerid bivalveChamelea gallina(L.), viz.C. gallina s.s.andC. striatula, were electrophoretically compared at seven polymorphic enzyme loci. In three populations from the Ría Formosa (southern Portugal), both morphotypes occurred sympatrically. Analyses of genotype frequencies in these mixed populations revealed departures from Hardy-Weinberg expectations at nearly all loci. These deviations were mainly attributable to a Wahlund effect, caused by mixing the two morphotypes. Nei's mean unbiased genetic distance between the two forms wasD=1·138, while the mean genetic distances between populations within morphotypes were D=0·083 inC. gallina s.s.andD=0·229 inC. striatula. It is therefore concluded thatC. gallinaandC. striatulaare reproductively isolated (biological) species, the geographical distribution of which is outlined.