The induction of gynogenetic diploids during meiosis II in the scallop Chlamys farreri was attempted using the treatments of cytochalasin B (0.5 μg ml−1; CB)
and 6-dimethylaminopurine (60 μg ml−1; 6-DMAP). The effects of CB
and 6-DMAP treatments on meiosis and fertilization of eggs were also
examined. Haploid gynogenesis was induced by sperm which were
ultraviolet-irradiated for 30 s at an intensity of 2561 μW cm−2 s−1.
CB and 6-DMAP treatments were highly effective in suppressing
meiosis II, yielding 19% and 28% gynogenetic diploids, respectively.
Compared with the CB treatment, the 6-DMAP treatment produced more expected
D-shaped larvae. Cytological observations revealed that 6-DMAP inhibited
pronuclear movements and the segregation of chromosomes, resulting in the
formation of one big diploid female pronucleus with strong fluorescence,
while CB inhibited cytokinesis, resulting in two female pronuclei
formations. The UV-irradiated sperm nucleus developed into a male
pronucleus, but did not participate in karyokinesis at mitotic anaphase,
suggesting that gynogenetic diploids were induced in the scallop.