ABSTRACT
The evolution of sex change, as a life history strategic alternate to gonochorism, has been explained by the size advantage model (Ghiselin, 1969; Charnov, 1982). The model has been successful in explaining the adaptive signifi cance of protogynous hermaphroditism in animals. If reproductive success increases with size or age more rapidly for one sex, an individual that changes sex in the appropriate direction will have a longer life of reproductive success (see also van Rooij and Videler, 1997) than that which does not change sex. If males gain in reproductive success with size or age faster than females, as in most cases, protogynous sex change is favoured; the opposite situation favours protandry. The model predicts protogyny, where large males monopolize mating. In most protogynous haremic social systems, large males control access to females (Munoz and Warner, 2003).
