Behavioral Ecology Vol. 13 No. 1: 75-82
© 2002 International Society for Behavioral Ecology
Modeling spawning strategy for sex change under social control in haremic angelfishes
a Department of Information and Computer Sciences, Nara Women's University, Kita-Uoya Nishimachi, Nara 630-8506, Japan b Kyushu International University, Hirano, Yahata-Higashi-ku, Kitakyushu 805-8512, Japan
Address correspondence to N. Shigesada. E-mail: sigesada{at}ics.nara-wu.ac.jp . Y. Sakai is now at the Faculty of Applied Biological Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, Japan.
In haremic angelfishes where protogynous (female to male) sex change is favored, females have been reported to adopt several tactics for earlier sex change on the basis of a trade-off between reproduction and growth, or survivorship. A recent field study on Centropyge ferrugatus revealed that females reduce spawning frequency in competition with similar-sized neighbors for social dominance. To evaluate the optimal spawning strategy taken by haremic fishes, we developed an evolutionarily stable strategy model that focuses on their life history and social structure based on field data of C. ferrugatus. The results of the analysis predict that the spawning frequency will be low when the mortality rate of females is high compared with males, the harem size is large, and there is a moderate degree of social control. Our model further predicts conditions under which females completely stop spawning, as if they have become bachelors. Thus, the regulated spawning frequency may be taken as a strategy to optimize the reproductive success of an individual in response to the available choices for sex change, social control, and environmental conditions. Social control would also play an important role in sex change in many other haremic species.
Key words: angelfish, bachelor sex change, Centropyge ferrugatus, harem-fission sex change, social control, spawning frequency, takeover sex change.