Maternal variability in the
blacklip abalone, Haliotis rubra leach (Mollusca: Gastropoda): effect
of egg size on fertilisation success
S.M.H Huchette, J.P. Soulard, C.S. Koh, R.W. Day-2004
Aquaculture, 231(1-4): 181-195
Abstract:
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 5×106 and 108 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.
(Department of Zoology, The University of Melbourne,
Melbourne, Victoria, Australia, e-mail: sylvain.huchette@wanadoo.fr)