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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.
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