title: Spermatozeugmata structure and dissociation of the Australian flat oyster Ostera angasi: Implications for reproductive strategy.
abstract: Variation in reproductive strategy is one of the key factors contributing to recruitment success of molluscs in different habitats. Spermcasting is a unique mode in mollusc reproduction where males produce spermatozeugmata, a radially arrayed sperm cluster wrapped by gelatinous membrane. In this study, spermatozeugmata structure and their dissociation in the Australian flat oyster Ostrea angasi were investigated to elucidate the reproductive strategy in spermcasting molluscs. The histological observation indicated that spermatogonia gradually aggregated in the gonad follicle at the early gonad development stages and developed into spermatozeugmata and became tightly packed at the advanced stages. Even though mature male and female gametes could be found in a hermaphroditic individual, the animal may prevent self-fertilization by shedding different sex gametes at different time. The O. angasi sperm are similar in size and shape to broadcasting oysters, but have one additional mitochondrion. Variations in maintaining spermatozeugmata integrity and sperm motility between individuals depended on the level of masculinity or femineity. The durations of spermatozeugmata dissociation and sperm viability were longer in males than in hermaphrodites. The unique structure and capability for spermatozeugmata to maintain the functional integrity after spawning have adaptive significance for fertilization and gamete dispersal in this species.
authors.affiliation: School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia; Department of Fisheries Biology and Genetics, Hajee Mohammad Danesh Science and Technology University, Dinajpur 5200, Bangladesh.
authors.forename: Md Mahbubul
authors.initials: MM
authors.lastname: Hassan
authors.affiliation: School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia.
authors.forename: Jian G
authors.initials: JG
authors.lastname: Qin
authors.affiliation: Aquatic Sciences, South Australian Research and Development Institute, West Beach, SA, Australia. Electronic address: xiaoxu.li@sa.gov.au.
authors.forename: Xiaoxu
authors.initials: X
authors.lastname: Li
mesh_terms: D000818:Animals; D001315:Australia; D005260:Female; D006801:Humans; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D010125:Ostreidae / Q000254:growth & development* / Q000378:metabolism; D010063:Ovum / Q000254:growth & development / Q000378:metabolism; D012098:Reproduction / Q000235:genetics*; D013081:Sperm Motility / Q000235:genetics; D013093:Spermatogonia / Q000254:growth & development / Q000378:metabolism; D013094:Spermatozoa / Q000254:growth & development* / Q000378:metabolism
keywords: Hermaphrodite; Mollusc; Sperm; Spermcasting