ATLANTA - While changing sex from female to male, the highly socialbluebanded goby becomes more aggressive. At the same time, theconversion of testosterone to estrogen slows in the brain, but isunaffected in the changing gonads, according to a Center for BehavioralNeuroscience (CBN) study in the current on-line edition of Proceedingsof the Royal Society B. The finding, which suggests the initial stagesof sex change in fish are regulated in the brain, could help betterexplain the biological basis of human sexual identity.
Like many fish species, the bluebanded goby switches sex in response tochanges in its social environment. In a socially stable group, removalof the dominant male typically results in the dominant female changingsex to fill the void. During this process, the female experiences anarray of behavioral changes and the transformation of her sex organs tomale.
In the study, CBN researcher and Georgia State University biologyprofessor Matthew Grober, PhD, CBN and Georgia State post-doctoralfellow Michael Black, PhD, and researchers Jacques Balthazart, PhD, andMichelle Baillien, PhD, of the Center for Cellular and MolecularNeurobiology at the University of Liege in Belgium, attempted todetermine the correlation between behavior and sex hormone conversionin four groups of gobies: a control group of females; a control groupof males; dominant females who were beginning to change to males;dominant females who recently changed sex to males.
The researchers measured the activity of aromatase, an enzyme thatconverts testosterone to estrogen, in the gonads and the brain.Previous studies have implicated aromatase in sexual development in avariety of vertebrates, including humans. The researchers found thatdominant, sex-changing females and recently sex-changed males had lowerbrain aromatase levels than control females. Control males had thelowest brain aromatase levels and lower gonadal aromatase levels thanall groups, except the sex-changing females.
In response to the removal of dominant males from their social groups,sex-changing females displayed more aggressive behavior thatcorresponded with lower brain aromatase levels. Fish with the lowestbrain aromatase levels had the greatest relative increase in aggressivebehavior.
"Our finding suggests social cues rapidly initiate the sex changeprocess in the brain which eventually influences behavioral and gonadaltransformation," said Grober.
The researchers' next step is to determine whether aromatase activityaffects aggression or aggression influences aromatase activity. "Thisstudy shows us that sexual identity involves a complex interplay amongthe brain, physiology and behavior," said Grober. "If you accept sexualvariation is a part of the normal human condition, we can ask questionsin fish that may tell us more about who we are."
CBN, a NationalScience Foundation (NSF) Science and Technology Center, is a researchand education consortium of eight metro Atlanta colleges anduniversities, including lead institution Georgia State University,Emory University, Georgia Institute of Technology and the fiveinstitutions of the Atlanta University Center (Morehouse College,Morehouse School of Medicine, Spelman College, Clark Atlanta Universityand Morris Brown College). More than 90 neuroscientists lead theresearch program to understand the neurobiology of complex socialbehaviors. CBN studies have led to a breakthrough treatment foranxiety-related disorders and new understanding of the neural basis ofsocial bonding between animals. In addition to research, CBN has acomprehensive education program designed to improve science literacyand attract more women and underrepresented minorities to neuroscienceprograms. The center is supported by more than $53 million in grantsfrom NSF and the Georgia Research Alliance.
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