Polyploidy in the Manila clam Ruditapes philippinarum. 1. Chemical induction and larval performances of triploids.
Triploidy was induced by treating fertilized eggs with cytochalasin B (1 mg in 1 ml DMSO in 1 litre of seawater). The percentage of triploid embryos and spat was assessed by karyological examination. The optimal treatment was 15 min exposure to cytochalasin at 25° starting 20-35 min after insemination, which produced an av. of 75.8±5.7% triploid embryos over 4 experiments. Growth and survival of larvae to metamorphosis were recorded. In 2 replicates, larvae showed similar survival up to settlement (19.3 and 27.0% of that of larvae from untreated control eggs). Mean shell length of larvae from treated eggs was significantly shorter than that of the controls in one of the replicates, where mortality of triploids relative to diploids within the treated group was low (21.0%). This difference did not occur in the other replicate, where a mortality of triploids relative to diploids within the treated group was high (64.5%).