Tetraploid induction by meiosis inhibition in the dwarf surfclam Mulinia lateralis (Say 1822): effects of cytochalasin B duration

Abstract

Different durations of a cytochalasin B (CB) treatment were tested for tetraploid induction by meiosis inhibition in the dwarf surfclam Mulinia lateralis Say. Cytochalasin B, 0.67 mg L−1, was applied to newly fertilized eggs at 8–10-min post fertilization and removed when in the untreated eggs: (1) Polar body 1 (PB1) was released in 90% of the eggs and polar body 2 (PB2) began to form (T1); (2) Polar body 2 was released in about 25–30% of the eggs (T2); (3) Polar body 2 was released in about 70–75% of the eggs (T3); or (4) eggs began to enter mitosis I or the polar lobe began to form (T4). Three replicates were produced using different sets of parents. The ploidy of resultant larvae and juveniles was determined by flow cytometry. Blocking PB1 alone in T1 groups produced mostly tetraploids, and longer CB treatments in T2 and T3 resulted in increasing numbers of pentaploids. In T4 groups where both PB1 and PB2 were inhibited, larvae were predominantly pentaploids. Pentaploid larvae were arrested at the trochophore stage. The majority of tetraploid larvae died as trochophores, although a small fraction reached D-stage. Among 478 juvenile clams sampled from a T1 group, three (0.6%) were confirmed as tetraploids. This study shows that tetraploid embryos can be produced at high efficiencies (40–90%) by blocking meiosis I. Tetraploids produced by meiosis inhibition in normal eggs are viable in M. lateralis, but their survival beyond metamorphosis is extremely low.