Date of Award

Summer 8-12-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Dr. Matthew Grober

Second Advisor

Dr. Laura Carruth

Third Advisor

Dr. Andrew Clancy

Fourth Advisor

Dr. Giovanni Gadda

Fifth Advisor

Dr. Walter Walthall

Abstract

During the lifetime of an organism, key events are orchestrated by a confluence of environmental, social, and physiological factors to promote reproductive success. Steroid hormones are critical regulators of fundamental aspects of reproductive life history, including gametogenesis, secondary sexual characteristics, sexual behavior, territory establishment and defense, and parenting. The steroid hormones investigated herein (testosterone (T), 11-ketotestosterone (KT), 17b-estradiol (E2) and cortisol) are linked through steroidogenic conversion pathways. This dissertation utilized an integrative approach to investigate the neuroendocrine and social contexts that regulate transitions among phenotypes in a bi-directionally hermaphroditic haremic fish, Lythrypnus dalli. Conventional sex roles are reversed, such that only males provide nest care, females exhibit intra-sexual competition and male reproductive success is associated with female courtship solicitation. Females living in stable social groups maintain dramatic differences in status, morphology, and tissue T, KT, E2, and cortisol. Parasitic male morphs, mini males, do not defend territories and have morph-typical water-borne and tissue profiles of T, E2, and KT. Two life history transitions, socially induced sex change and male parenting, are associated with increase in rates of behavior and KT levels. The regulation of these life history transitions by KT was investigated via two types of endocrine manipulations. Coupling systemic KT implants with a social context permissive to sex change caused rapid, but transient effects on agonistic behavior in dominant females, and secondary effects on subordinates during a period of social instability. Despite elevated brain and systemic KT 5 d after implant, overall rates of aggressive behavior remained unaffected, demonstrating a key role for context in regulating steroid associated changes in behavior. Intracerebroventricular inhibition of the enzyme 11b-hydroxysteroid dehydrogenase, reduced KT, elevated cortisol, and reduced male parenting behavior. 11-Ketotestosterone rapidly rescued parenting when administered along with the inhibitor, while cortisol had no effects on parenting. During reduced male nest attendance caused by KT inhibition, dominant, but not subordinate females, exhibited transient parenting and elevated brain KT. Taken together, rapid and/or local modulation of steroids allows for context-specific regulation of dynamic changes in behavior in an environment that requires an organism to successfully coordinate multiple activities to enhance fitness.

DOI

https://doi.org/10.57709/5815431

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