There are two major behavioral mechanisms which have been proposed to be responsible for instigating protogynous sex-change, disinhibition and stimulation (Shapiro, 1988). Disinhibition (also called suppressionl; see Ross, 1990) implies that the presence of a male will prevent females from changing sex, and upon removal of that male, the female will switch sex. Conversely, if the female is separated from the male, she could be stimulated to change sex (also called induction; Ross, 1990). From the research conducted, it appears that the supression model only requires one environmental stimulus, while stimulation requires two environmental stimuli (Ross, 1990).
These two strategies are quite similar, yet many experiment have been conducted to prove each.
Female Anthias squamipinnis have been found to change sex when female-male behavioral interaction is eliminated (Shapiro, 1983). Sequential removal of males from a social group of Anthias squamipinnis led to a one-to-one replacement of males by sex-changing females (Shapiro, 1980).
Many members of the family Labridae control sex-change socially. The Red Sea razorfish (Xyrichthys pentadactylus) changes sex via socially controlled stimuli: removal of the males stimulates the females to change sex (Nemtzov, 1985). In a cleaner wrasse (Labroides dimidiatus), the presence of a male in a harem represses the female ability to change sex; and the death of the dominant male stimulates sex-change of the larges female within the harem (Robertson, 1972).
A study by Ross et al. (1983) on the saddleback wrasse (Thalassoma duperrey) has sugggested that there exists a threshold value of the proportion of larger or smaller fish within a home range which stimulates such a change. At least one smaller conspecific must be present to stimulate sex-change in another fish.
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