Sex change evolution and cost of reproduction

Sex change evolution is studied theoretically. I developed an analysis based on dynamic programming to confirm the evolutionary stability in a wide class of sexual schedules and to show how various mechanisms are combined to determine the sex change evolution. First, it is shown that the evolutionarily stable sexual strategy may include an extended nonreproductive period that intervenes between male and female phases, if reproductively active individuals suffer costs of enhanced mortality or reduced growth rate, in addition to the sexual difference in the way fertility increases with size (or age). This pattern corresponds to "early sex changer" observed among several coral reef fish species. Second, I show that the difference between sexes either in mortality or in growth rate favors the evolution of sex changer even if the size advantage is the same between the two sexes. This confirms two alternative mechanisms (mortality-advantage model and growth-rate-advantage model) for sex change evolution. [Behav Ecol 1991; 2: 56-68]