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 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 N-i of competitors at each spawning exactly. Males can vary the mass m of their sperm and the number s(i) at a spawning. The aim is to find the evolutionarily stable strategies and hence the way that m and s(i) vary with N-i. 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 s(i)*. These are solved numerically. (C) 1997 Academic Press Limited.