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First published online October 19, 2007
Journal of Experimental Biology 210, 3720-3727 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.008417

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Sperm release strategies in marine broadcast spawners: the costs of releasing sperm quickly

Dustin J. Marshall^1,* and Toby F. Bolton²

¹ School of Integrative Biology/Centre for Marine Studies, University of Queensland, 4072, QLD, Australia
² Lincoln Marine Science Centre, School of Biological Sciences, Flinders University, 5606, SA, Australia

View larger version (6K): [in this window] [in a new window]   Fig. 1. Fertilisation success (mean ± s.e.m.) of simulated fast (open bars) or slow (shaded bars) sperm release rates across two groups of Galeolaria caespitosa eggs in a flume. (A) Fertilisation success of the upstream group of eggs; (B) fertilisation success in the downstream group of eggs.

View larger version (9K): [in this window] [in a new window]   Fig. 2. Effect of prior exposure of sperm to unfertilised or recently (1–10 min post exposure) fertilised eggs on (A) sperm concentration and (B) subsequent fertilisation success in Galeolaria caespitosa. All values are means ± s.e.m.; open bars indicate the control (C), lightly shaded bars indicate exposure to recently fertilised eggs (1 and 10 min post fertilisation in A and 10 min post-fertilisation only in B), and black bars indicate exposure to unfertilised eggs (U).

View larger version (13K): [in this window] [in a new window]   Fig. 3. Diagram illustrating the consequences of different sperm release rates and permanent polyspermy block speeds on subsequent fertilisation success. Open circles represent unfertilised eggs; shaded circles represent fertilised eggs that have produced a permanent block to polyspermy; stippled circles represent fertilised eggs that have not yet formed a permanent block to polyspermy. (A) The consequences of a slow permanent polyspermy block combined with a fast sperm release rate. When additional sperm arrive at Time 3, the upstream, newly fertilised eggs have not yet formed a permanent polyspermy block and so sperm at time 3 are `wasted' on an already fertilised egg. (B) Consequences of a slower sperm release rate. Sperm arriving at eggs at Time 4 are not wasted on the upstream egg because sufficient time has passed for a permanent polyspermy block to form and overall success is higher. (C) Consequences of a (hypothetical) faster permanent polyspermy block, by the time sperm arrive at Time 3, the upstream egg is already impervious to further sperm attachment so no sperm is wasted. Overall then, changing the time until the permanent polyspermy block forms or changing the release rate of sperm has an effect on fertilisation success.

View larger version (82K): [in this window] [in a new window]   Fig. 4. Light micrograph of (A) unfertilised and (B) recently (within a few minutes) fertilised Galeolaria caespitosa eggs. Arrows in A indicate sperm that have attached to the outer region of the egg. The circle in B highlights the raised fertilisation `cone' where the sperm has entered the egg. Scale bars, 25 µm.