Date of Award

Spring 2005

Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Matthew S. Grober - Chair

Second Advisor

Deborah J. Baro

Third Advisor

Charles D. Derby

Fourth Advisor

Larry J. Young

Fifth Advisor

H. Elliott Albers


Social interactions can have profound effects on the behavior, physiology, and overall fitness of an individual. An example of this in Lythrypnus dalli is the removal of a male from a social group resulting in a dominant female fish changing sex. The dominant female's transformation involves a suite of changes including brain, behavior, morphology, and physiology. Following the social trigger (male removal), sex-changing individuals' morphology, steroid levels, and changes in the behavior were quantified in the field and compared to results found previously in the laboratory. There were lower rates of aggressive and courtship behavior in the field, but the change in behavior over time had a similar pattern and there were parallels in morphology and steroid levels between lab and field sex changers. The brains of dominant females also responded to social change. Aromatase, an enzyme that converts testosterone into estrogen, and oxytocin, a neuropeptide found in mammals, have been associated with vertebrate social and reproductive behavior. The fish homologue of oxytocin, isotocin, and aromatase are both found in L. dalli. Upon removal of a male from the social group, L. dalli dominant females experienced a decrease in the number of preoptic area isotocin-immunoreactive cells over the course of sex change (7-10 days) and a decrease in brain aromatase activity (bAA) levels within hours, but not minutes, of male removal, while gonadal aromatase activity (gAA) decreased at a much slower time scale (beyond a week). Hours, but not minutes, after male removal, the sex-changing individual's bAA correlated with aggressive behavior increases and not the amount of time following male removal. Males that had just changed from female had different gonadal allocation and higher bAA levels than established males. Subordinate females had high gAA, but their bAA was between that of males and sex changers. In conclusion, dramatic changes in anatomy and neuroendocrine function can occur in response to social cues, individuals with similar reproductive behavior and external morphology can have large neuroendocrine and internal morphologic variation, and social interactions can affect steroid metabolism locally on a short time scale independent of gonadal modulation of steroids.


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