Differential Responses of Brain, Gonad and Muscle Steroid Levels to Changes in Social Status and Sex in a Sequential and Bidirectional Hermaphroditic Fish

Abstract

Sex steroids can both modulate and be modulated by behavior, and their actions are mediated by complex interactions among multiple hormone sources and targets. While gonadal steroids delivered via circulation can affect behavior, changes in local brain steroid synthesis also can modulate behavior. The relative steroid load across different tissues and the association of these levels with rates of behavior have not been well studied. The bluebanded goby (Lythrypnus dalli) is a sex changing fish in which social status determines sexual phenotype. We examined changes in steroid levels in brain, gonad and body muscle at either 24 hours or 6 days after social induction of protogynous sex change, and from individuals in stable social groups not undergoing sex change. For each tissue, we measured levels of estradiol (E2), testosterone (T) and 11-ketotestosterone (KT). Females had more T than males in the gonads, and more E2 in all tissues but there was no sex difference in KT. For both sexes, E2 was higher in the gonad than in other tissues while androgens were higher in the brain. During sex change, brain T levels dropped while brain KT increased, and brain E2 levels did not change. We found a positive relationship between androgens and aggression in the most dominant females but only when the male was removed from the social group. The results demonstrate that steroid levels are responsive to changes in the social environment, and that their concentrations vary in different tissues. Also, we suggest that rapid changes in brain androgen levels might be important in inducing behavioral and/or morphological changes associated with protogynous sex change.

A mechanism for rapid neurosteroidal regulation of parenting behaviour

“…This is accompanied by rapid reduction in brain aromatase activity, thus providing a mechanism for a local reduction in brain E 2 [21]. Brain KT also increases in females during sex change and this could occur via an increase in brain 11b-HSD activity [21,32]. Here, in the absence of males occupying the nest and caring for eggs, opportunistic females rapidly monopolized these resources.…”

“…Third, brain KT levels are equal to or higher than gonad KT, suggesting that the brain is an important de novo producer of KT [32,33]. Finally, brain and gonadal KT levels are not correlated [32].…”

“…Second, there are no sex differences between females and non-parenting males in levels of systemic, brain and gonad KT [31,32]. Third, brain KT levels are equal to or higher than gonad KT, suggesting that the brain is an important de novo producer of KT [32,33]. Finally, brain and gonadal KT levels are not correlated [32].…”

“…First, parenting males exude high levels of KT in water compared with males not actively parenting and compared with females [5]. Second, there are no sex differences between females and non-parenting males in levels of systemic, brain and gonad KT [31,32]. Third, brain KT levels are equal to or higher than gonad KT, suggesting that the brain is an important de novo producer of KT [32,33].…”

“…At the end of the 60 min behaviour observations, females were euthanized, and their brain and gonad tissues were immediately collected, frozen on dry ice and maintained at 2808C until assayed. Steroid hormone extractions were conducted using previously described techniques [32,36] (see the electronic supplementary material for details), and differences in tissue KT of parenting versus non-parenting a-females were analysed using unpaired t-tests.…”