Parthenogenetic development of dwarf surf dam,Mulinia lateralis, oocytes treated with polar body suppressing agents

Abstract

Parthenogenesis following oocyte activation has been observed in a number of marine invertebrates, but the fate of parthenogenesis in bivalve mollusc embryos is unclear. We used the dwarf surf clam, Mulinia lateralis, to examine parthenogenetic development of KC1-activated oocytes using the polar body suppressing agents caffeine and heat or cytochalasin B. Development was followed by epifluorescence microscopy and flowcytometric analysis using the DNA-specific fluorochrome DAPI. All agents suppressed polar body formation to some degree, putatively increasing the ploidy level and retaining a meiotic centrosome in the zygote; but the zygotes failed to develop normally. Failure of the zygotes to develop suggests that the meiotic centrosome is incapable of participating in mitosis in bivalves.

Effects of cytochalasin B on fertilization and ploidy in the Pacific oysterCrassostrea gigas

“…In fact, we ob scrved, as in Scarpa et al (1993), that the first division was later (70 min) in the treated embryos than in the control (50 min), which may also be a consequence of spermatie inhibition. Scarpa et al (1992) suggested that the absence of sperm in gynogenetic induction cou Id prevent l'irst mitosis, c1eavage and subsequent clevelopmcnt because of the absence of a paternal centrosome and Diter and Dufy (1990) that the first mitotic division and cleavage would be delayed by this means but that development could resume later. How ever, Hei Ibrunn (1925) suggested for Cummingia (Mollusca) and Washitani-Nemoto et al (1994) for As/erina pec/imfera (Echinodermata) that the inhibi tion ofpolar body expulsion in unfertilized eggs couId compensate for this lack of centrosome due to the presence of meiotic centrosomes which would allow normal mitosis and first cleavage to take place.…”