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.