Incidental production of tetraploid Manila clams, Tapes philippinarum (Adams and Reeve).
For about 10 years the quest for tetraploid bivalves has eluded researchers, leading to doubts that tetraploids were viable. Recently 2 reports of tetraploid shellfish have led to increased optimism. This study documents a 3rd species in which tetraploids are viable. Newly fertilized eggs of the Manila clam were treated with cytochalasin B from 20 to 40 min after fertilization to induce triploidy. Following standard nursery culture, juveniles were planted at 2 locations for analysis of growth differences between diploid and triploid clams. Samples from the planted populations were taken at regular intervals from Mar. 1993. Of 200 clams sampled from the Welsh (UK) site, 1 was unequivocally tetraploid; of 120 clams sampled in Israel, 2 were tetraploid, and 2 were hypotetraploid. Tetraploids formed gametes with eggs about 41% larger than diploids. Tetraploids were produced as an artefact of triploidy induction, either from inhibition of the 1st polar body alone or in combination with the 2nd, or by inhibition of the 1st mitotic division. Production of artefact groups like tetraploids suggested that development of the eggs was asynchronous. The major implication of these findings is that tetraploidy can be tolerated in T. philippinarum and apparently at least in 2 other species, and some evidence exists for gamete production.