title: Be a good loser: A theoretical model for subordinate decision-making on bi-directional sex change in haremic fishes.
abstract: Among animals living in groups with reproductive skew associated with a dominance hierarchy, subordinates may do best by using various alternative tactics. Sequential hermaphrodites or sex changers adopt a unique solution, that is, being the sex with weaker skew when they are small and subordinate, and changing sex when they become larger. In bi-directionally sex-changing fishes, although most are haremic and basically protogynous, subordinate males can change sex to being females. We study a mathematical model to examine when and why such reversed sex change is more adaptive than dispersal to take over another harem. We attempt to examine previously proposed hypotheses that the risk of dispersal and low density favor reversed sex change, and to specify an optimal decision-making strategy for subordinates. As a result, while the size-dependent conditional strategy in which smaller males tend to change sex is predicted, even large males are predicted to change sex under low density and/or high risk of dispersal, supporting both previous hypotheses. The importance of spatiotemporal variation of social and ecological conditions is also suggested. We discuss a unified framework to understand hermaphroditic and gonochoristic societies.
authors.affiliation: Department of Evolutionary Studies of Biosystems, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Kanagawa 240-0193, Japan. Electronic address: sawada@anet.soken.ac.jp.
authors.forename: Kota
authors.initials: K
authors.lastname: Sawada
authors.affiliation: Department of Information Systems Creation, Faculty of Engineering, Kanagawa University, Yokohama, Kanagawa 221-8686, Japan.
authors.forename: Sachi
authors.initials: S
authors.lastname: Yamaguchi
authors.affiliation: Department of Biology, Faculty of Sciences, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Yoh
authors.initials: Y
authors.lastname: Iwasa
mesh_terms: D000818:Animals; D049628:Body Size / Q000502:physiology; D005260:Female; D005399:Fishes; D057850:Hermaphroditic Organisms / Q000502:physiology*; D008297:Male; D008962:Models, Theoretical; D011156:Population Density; D012726:Sexual Behavior, Animal; D012930:Social Dominance; D062211:Spatio-Temporal Analysis
keywords: Conditional strategy; Hermaphroditism; Reproductive skew; Sexual plasticity