Induced triploidy in the soft-shelled clam Mya arenaria: energetic implications

Abstract

Given that triploid adult bivalves reportedly grow larger and faster than their diploid siblings, such differences should be traceable to variation in energy allocation. In one proposed mechanism, retarded gametogenesis found in triploid adults may allow them more energy for somatic growth. Another hypothesis states that triploids are more heterozygous; increased heterozygosity has been positively correlated with enhanced growth. Juvenile soft-shelled clams, Mya arenaria, were treated with cytochalasin B to induce triploidy and examined with respect to components of a balanced energy equation (C=P+R+E). The variables measured were oxygen uptake (Vo2), filtration rate (FR), dry tissue weight, shell length, shell height and shell inflation. Energy budgets were constructed and diploid and triploid groups compared. Few significant differences were found between diploid and triploid juvenile clams with respect to energy budget components. However, at seven loci assayed electrophoretically the triploid individuals were nearly twice as heterozygous as their diploid siblings. Moreover, tripoloid variances were less than diploid variances for every variable measured. Increased heterozygosity has been correlated with the decreased variance of morphological parameters. This study is believed to be the first to show decreased variance of physiological properties as well as morphological characters. Overall the data clearly indicate that energy allocation in juvenile M. arenaria is not related to ploidy.