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The ability of an animal to respond and adapt to stimuli is necessary for its survival and involves plasticity and coordination of multiple levels of biological organization, including behavior, tissue organization, hormones, and gene expression. Each of these levels of response is complex, and none of them responds to stimuli in isolation. Thus, to understand how each system responds, it is necessary to consider its role in the context of the entire organism. Here, I have used the African cichlid fish Astatotilapia burtoni and its extraordinary phenotypic plasticity to investigate how animals respond to a change in social status from subordinate to dominant and attempted to integrate these multiple levels of biological response, as well as the roles of several candidate neuromodulators,. First, I have described how male A. burtoni become more aggressive and reproductive during their transition to dominance as well as increasing circulating levels of testosterone and estradiol and the histological organization of their testes. I then mapped the distribution of expression of two behaviorally relevant neuropeptides, arginine vasotocin and isotocin, and their respective receptors, throughout the A. burtoni brain, and found that they were highly expressed in several brain areas important for social behavior and decision-making. I then investigated the role of arginine vasotocin in social status and behavior via pharmacological manipulation and qPCR, showing the importance of arginine vasotocin in controlling the transition to dominance. Lastly, I investigated the role of aromatase, testosterone, and estradiol in male A. burtoni, both in stable dominant males and in males as they transition to dominance, using pharmacological manipulation and quantitative radioactive in situ hybridization, illustrating that estradiol synthesis during dominance is dependent on aromatase activity and necessary for aggressive behavior. / text

The neuropeptides arginine-vasotocin (AVT) and corticotropin-releasing hormone (CRH) are involved in the hypothalamic-pituitary-interrenal (HPI) axis. During stress, the HPI axis is activated and cortisol is released into the blood. In addition to their role in the HPI axis, AVT and CRH also have behavioural effects. The roles of AVT and CRH in stress responses and agonistic behaviour were studied in this thesis, using two different models. In the first model, two strains of rainbow trout (Onchorhynchus mykiss) divergent in stress-induced release of cortisol were investigated. This was done by observing behaviour and stress responses under different conditions. These strains were found to have divergent stress coping strategies based on the observed behaviour and levels of plasma cortisol. This divergence in behaviour could be associated with the CRH system, since the mRNA levels of CRH differed between the strains during stress. However, no differences between strains were observed in AVT or its receptor expressions. In the second model, non-selected rainbow trout were paired and the effect of intracerebroventricular (icv) injections of an active substance (AVT, CRH or the CRH related peptide Urotensin-I (UI)) on fights for dominance was investigated. One fish of the pair received the active substance icv and the other received saline icv. Fish receiving AVT became subordinate in accordance with the suggestion that AVT attenuates aggression in territorial vertebrates. Fish receiving CRH became subordinate whereas UI showed no effect on fights for dominance. Further, both CRH and UI induced an anxiety-related behaviour similar to non-ambulatory motor activity in rats. In addition, CRH appeared to affect the dopaminergic and serotonergic systems. In this thesis, it is suggested that CRH is involved in the behavioural modulation of the stress coping strategies in teleost fish. Further, AVT and CRH seem to act inhibitory on aggressive behaviour.

The aim of this study was to compare the effects of arginine vasotocin (AVT) administration in the endangered boreal toad (Bufo boreas boreas) and common Fowler’s toad (Bufo fowleri). The objectives of this study were to determine if AVT could elicit: 1) calling, and 2) amplexus behaviors. Toads were paired into single male:female groups and administered AVT at varying concentrations: 0.1, 1.0, 5.0, 10.0 and 25.0 μg/g and in different combinations: 1) only male was treated; 2) only female was treated, and 3) both male and female treated. AVT failed to stimulate any breeding behavior in the boreal toad, but the administration of AVT to both B. Fowleri genders significantly affected the duration of amplexus (p<0.0347). Also, the concentration of AVT significantly affected the length of amplexus (p<0.0429) and call frequency (p<0.0294). These results will be valuable for breeding programs where animals are failing to show natural reproductive behavior.

Hermaphroditism, associated with territoriality and dominance behavior, is common in the marine environment. Male sex-specific coloration patterns and behavior are particularly evident in species where males are territorial and guard harems of females such as wrasses and groupers. Protogynous hermaphrodites that change sex from female to male are good models to study sexual behavior and related changes in the brain due to their abilities to reorganize their sexual phenotype as adults. Two hormones produced in the brain and implicated in the process of sex-specific behavior and reproductive development are arginine vasotocin (AVT) and gonadotropin releasing hormone (GnRH). While a wealth of data exists regarding these hormone systems separately, little is known about linkage between these two systems. Especially there is no data tracking these two systems together in any protogynous fish. This study was conducted to test the hypothesis that coordinated interactions between AVT and GnRH facilitate the process of behavioral and gonadal sex change in the rock hind Epinephelus adscensionis. Four topics were addressed to investigate the relationship between behavior and reproduction: i) rock hind sex change, sexual characteristics and conditions causing sex change to occur in captivity were detailed as a basis for examining the AVT system and GnRH during this process, ii) the distribution of a vasotocin V1a type receptor identified in rock hind brain was examined for the first time in a fish species using a custom designed antibody then the receptor protein was co-localized with GnRH producing cells within the brain to confirm that a pathway exists for AVT action on GnRH, iii) levels of AVT, AVT receptors, and GnRH messenger RNA (mRNA) were compared between male and female rock hind phenotypes, and iv) female rock hind at early stages of sex change were compared for brain mRNA expression of AVT, AVT receptors, and GnRH to determine the order of hormonal change during the process of sexual inversion in this species. This study provides a better understanding of the relationship between sex-specific behavior and reproductive development via AVT and GnRH systems that are conserved in all vertebrates. / text