An integrative approach to sex change: social, behavioural and neurochemical changes in Lythrypnus dalli (Pisces)
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This study examined three aspects of protogynous sex change in Lythrypnus dalli (Gobiidae): (1) social influences on the rate of sex change, (2) the sequence of behavioural changes, and (3) neuroendocrine changes. Social groups consisted of either four females, or four females with a male who was subsequently removed. Sex change occurred most rapidly in male- removed groups when the sex changer was larger than other females. Sex changers in female only groups and sex changers not larger than other females in male-removed groups changed sex at similar rates. These differences may be explained by two factors that affect dominance: prior knowledge of the social group and greater size. Sex changers were dominant to other females prior to male removal, and larger sex changers increased displacement rates three-fold immediately after male removal. Sex changers in the other groups did not show this increase in displacements. This early establishment of dominance accounts for the overall difference in the rate of sex change. Prior to spawning, however, all sex changers increased displacements and performed male-typical displays. Arginine vasotocin-immunoreactive forebrain cells of sex changers were similar in size to field-collected males, and larger than field-collected females. Previously nesting males also changed sex in male-only groups, but at slow rates. These data are combined with those of existing studies to generate an integrative model of sex change in this goby.
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