title: Sex determination and polyploid gigantism in the dwarf surfclam (Mulinia lateralis Say).
abstract: Mulinia lateralis, the dwarf surfclam, is a suitable model for bivalve genetics because it is hardy and has a short generation time. In this study, gynogenetic and triploid M. lateralis were successfully induced. For gynogenesis, eggs were fertilized with sperm irradiated with ultraviolet light and subsequently treated with cytochalasin B to block the release of the second polar body (PB2). Triploidy was induced by blocking PB2 in normally fertilized eggs. The survival of gynogenetic diploids was very low, only 0.7% to 8 days post-fertilization (PF), compared with 15.2% in the triploid groups and 27.5% in the normal diploid control. Larvae in all groups metamorphosed at 8-10 days PF, and there was no significant post-larval mortality. At sexual maturation (2-3 months PF), all gynogenetic diploids were female, and there was no significant difference (P > 0.05) in sex ratio between diploids and triploids. These results suggested that the dwarf surfclam may have an XX-female, XY-male sex determination with Y-domination. Compared with diploids, triploids had a relative fecundity of 59% for females and 80% for males. Eggs produced by triploid females were 53% larger (P < 0.001) in volume than those from diploid females. In both length and weight measurements at three months PF, the gynogenetic diploids were not significantly (P > 0.33) different from normal diploid females, suggesting that inbreeding depression was minimal in meiosis II gynogens. Triploid clams were significantly larger (P < 0.001) than normal diploids. We hypothesize that the increased body-size in triploids was caused by a polyploid gigantism due to the increased cell volume and a lack of cell-number compensation.
authors.affiliation: Haskin Shellfish Research Laboratory, Rutgers University, Port Norris, New Jersey 08349.
authors.forename: X
authors.initials: X
authors.lastname: Guo
authors.forename: S K
authors.initials: SK
authors.lastname: Allen
mesh_terms: D000818:Animals; D049872:Bivalvia / Q000235:genetics / Q000502:physiology*; D001824:Body Constitution; D048429:Cell Size; D003571:Cytochalasin B / Q000494:pharmacology; D005260:Female; D005298:Fertility; D005877:Gigantism; D008297:Male; D011123:Polyploidy; D012732:Sex Determination Analysis; D013094:Spermatozoa / Q000528:radiation effects; D014466:Ultraviolet Rays; D015053:Zygote / Q000187:drug effects
chemical_list: D003571:Cytochalasin B