Alternative spawning tactics of female angelfish according to two different contexts of sex change

Social conditions for sex change and reproductive success werestudied in the haremic marine angelfish, Centropyge ferrugatus,in the coral reefs of southern Japan. In this species the largestfemale in a harem changed sex not only after disappearance ofthe dominant male but also occasionally in his presence. Inisolated harems containing two to three females, strict socialcontrol by the dominant male resulted in females changing sexonly after the male disappeared (takeover sex change). In haremsadjacent to each other, however, takeover sex change did notoccur even when one of the males disappeared. Instead, largeharems including more than four females were formed by fusionof two adjacent harems. In such large harems, the dominant malewas unable to socially prevent the largest female from changingsex later to acquire a portion of the harem (harem-fission sexchange). Females in adjacent harems spawned less frequentlyand tended to grow faster than those in isolated harems, probablyto gain an advantage in dominance status over neighbors of similarsize. Thus, females changed spawning frequencies according tothe two different contexts of sex change. The takeover tacticresults in higher fitness than the harem-fission tactic, whichshould be the best in the bad situation of adjacent harems.