Genetic structure of giant clam (<i>Tridacna derasa</i>) populations from reefs in the Indo-Pacific

Abstract

Large genetic differences were observed among the Great Barrier Reef (GBR), Fiji and Philippine populations of <i>Tridacna derasa</i> (Roding) sampled in 1989 and 1990 (Nei's unbiased genetic distance, D,=0.137 to 0.341). This result contrasted strongly with the low genetic distance (D=0.032) reported previously for the giant clam <i>T. maxima</i> over similar geographical scales. No significant genetic differentiation was observed among most populations from the GBR (mean D=0.007), consistent with the high gene exchange expected in this highly connected reef system. However, significant differentiation resulting from differences in the frequencies of less common alleles between the North-Central GBR and South GBR (Swain region) were observed. Historical isolation of blocks of the Central Indo-West Pacific from the GBR and present-day restrictions to gene exchange between the GBR, Fiji and the Philippines as a result of oceanographic current patterns, were thought to be responsible for the high degree of genetic differentiation of <i>T. derasa</i> populations. The relevance of these findings to clam mariculture and reef restocking are briefly discussed.