Induced triploidy in the soft-shell clam

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Abstract
Induced polyploidy has been suggested as a means of genetically enhancing commercially important aquatic species, but only one other report has addressed this methodology in invertebrates. Triploid soft-shell clam (Mya arenaria) juveniles were produced by treating eggs either at fertilization for 15 minutes or from 15 to 30 minutes after fertilization with 1 mg/I cytochalasin B. Cytochalasin treatment altered early developmental events in both treatment groups and indications of this disruption persisted throughout a 4-hour observation period. Diploid and putative polyploids were assayed at 9–12 months of age cytogenetically and electrophoretically. Diploid Mya had 2n = 34 modal chromosome count; triploids had a modal 3n = 50. An adaptation of fish chromosome technique produced the highest mitotic index. Electrophoretic assays were performed on the basis of relative staining intensities of the component bands of heterozygous phenotypes. Five enzyme loci were sufficiently resolved for semiquantitative comparisons: monomers Est-3, Pgm-2; dimers Est-D, 6Pgd-1,2; and the tetramer Sdh-2. Diploid phenotypes of 6Pgd displayed staining patterns indicating an apparent duplication of a previously single locus and accordingly is labelled 6Pgd-1,2. Electrophoresis was a more efficient, albeit conservative, means of analysis than cytogenetics. in tandem, the two techniques are highly complementary.