Animals display a wide range of social behaviors, including social behaviors such as aggression, mating, and parental care. An individual's ability to express the 'right' behavior in the appropriate context is vital to its success. For instance, individuals should engage in mating behavior during the appropriate life history stage (i.e. age, season) and avoid it in inappropriate contexts, such as in the presence of a predator. Neuroendocrine systems are key in allowing individuals to match their behavior to their current situation, as these systems affect behavior and are also responsive to changes in the environment and in an organism's internal state.Serotonin, a neuromodulator, and androgenic sex steroid hormones are key regulators of aggression and appear to play a central role in matching an organism's aggressive behavior to its social environment. For instance, in many social species living in dominance hierarchies, an individual's social status affects concentrations of serotonin and androgens. Serotonin is a known inhibitor of aggression, whereas androgens often facilitate the expression of aggression; accordingly, social dominance is often negatively correlated with serotonin concentrations and positively correlated with androgens. Still, these patterns are not universal, varying with sex, species, life history stage, and social context.Here, I examined the physiological, demographic, and environmental correlates of serotonin and androgens in a despotic, female-dominant species-the spotted hyena. Specifically, I focused on the relationship between social rank and serotonin/androgens, and its modulators. I first examined predictors of two androgens, testosterone (T) and androstenedione (A4), in pregnant female hyenas. I found a positive relationship between both androgens and social rank. However, this relationship was specific to pregnant females who had previously given birth (multiparous), apparently due to an increase in maternal androgens in high-ranking but not low-ranking females after the birth of their first litter.I then examined the relationship between T and social status in adult females across different reproductive states and social contexts, I found a positive correlation between T and social status in lactating and pregnant females, but not in nulliparous females; again, this pattern appeared to be driven by an increase in high-ranking female T concentrations associated with their first breeding experience. In a comparison of T concentrations in lactating females during periods of relative social stability and instability, I found that T concentrations in low- but not high- ranking females increased during periods of social instability, resulting in the disappearance of the usual positive correlation between social rank and T.Finally, I examined predictors of serotonin concentrations in both male and female hyenas across ontogeny. Serotonin was negatively correlated with social rank in female but not male spotted hyenas. Furthermore, social status at birth was particularly predictive of serotonin, as opposed to social status at the time of physiological sampling, indicating early life social environment may have lifelong effects on serotonergic function.Overall, I found that social status was an important predictor of androgen and serotonin concentrations, but that this relationship was dependent upon characteristics of the individual (e.g. sex, life history stage) and their social environment.
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