Sperm competition, male prudence and sperm-limited females

Sperm are produced in astronomical numbers compared with eggs, and there is good evidence that sperm competition is the force behind the evolution of many tiny sperm. However, sperm production inevitably has costs. Recent research shows that male ejaculate expenditure is dynamic in both time and space, and that males are sensitive to risks of sperm competition and can vary ejaculate size accordingly. We focus on studies showing that males assess mating status and relative fecundity of females, and reveal that modulation of ejaculate investment by males can sometimes result in sperm limitation for females.