Maternal variability in the blacklip abalone, Haliotis rubra leach (Mollusca: Gastropoda): effect of egg size on fertilisation success
2004
Huchette, S.M.H. | Soulard, J.P. | Koh, C.S. | Day, R.W.
Egg quality has important effects on the performance of invertebrate offspring. Abalone produce eggs variable in size and quality and this may be a strategy to balance the risks between egg size and egg number in a variable environment. Histological sections of mature ovaries are presented. Fertilisation of eggs from seven different females was carried out in the hatchery using a broad range of sperm concentrations to determine the optimum. Fertilised and non-fertilised eggs were measured to determine the importance of size for fertilisation. Optimum sperm concentration was found to be between 5x10(6) and 10(8) sperm per litre (approximately 10,000-200,000 sperm/egg ratios). The development of oocytes in the gonad before spawning was not uniform, resulting in eggs that varied in size. At suboptimal sperm concentrations, eggs with larger cytoplasm had more chance of being fertilised, regardless of their vitelline thickness or total vitelline diameter. This pattern was consistent within clutches and between females. Eggs were found to expand after spawning. We discuss the importance of producing variable sizes of eggs and speculate that this variability may be an adaptive response to a highly variable and unpredictable environment or part of a density-dependent regulatory mechanism.
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