Sperm competition games: inter- and intra-species results of a continuous external fertilization model.

We investigate the relationship between sperm competition intensity and sperm expenditure, both across species and within a species, using a two sperm competition models. In model 1, the males cannot assess the number of competitors, and their ejaculate effort is shaped by the average number <N> of competitors. In model 2, males can assess the number Ni of competitors at each spawning exactly. Males can vary the mass m of their sperm and the number si at a spawning. The aim is to find the evolutionarily stable strategies and hence the way that m and si vary with Ni. A continuous fertilization model in which the sperm have to swim in order to fertilize an egg is described. This is used to find simultaneous equations describing m and si. These are solved numerically.