Date of Award

12-18-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Neuroscience Institute

First Advisor

Matthew Grober

Second Advisor

Charles Derby

Third Advisor

Walt Wilczynski

Fourth Advisor

Larry Young

Abstract

Social species are faced with the challenge of navigating a lifetime of dynamic social contexts. Social behavior is a critical target for natural selection because expressing behaviors appropriate for a given social context has important fitness consequences. Context-specific behavior is promoted by proximate regulators that are reciprocally influenced by behavioral expression and the social environment, such as hormones and social experience. This dissertation utilizes an integrative approach to investigate the causes and consequences of variation in agonistic behavior in the bluebanded goby (Lythrypnus dalli) across a range of relevant social contexts. This highly social, sex changing fish forms linear hierarchies of a dominant male and multiple subordinate females, and patterns of agonistic interaction are strongly linked to reproduction. Social networks that adhere strictly to the hierarchical social structure, where dominants are aggressive to subordinates but not vice versa, excel reproductively. Interestingly, this behavioral pattern is influenced by fish at all levels of the social hierarchy. Aspects of reproduction, including female reproductive state, also feedback to alter the social network position of specific group members. The steroid hormones cortisol, 11-ketotestosterone, and estradiol can influence, and be influenced by, agonistic behavior and reproductive physiology, and all were implicated for different roles in L. dalli social groups. The “stress” hormone cortisol, for example, fluctuates with female reproductive state and is associated with individual and social network measures in stable social groups. Estradiol, in contrast, is associated almost exclusively with reproductive state and function. In social groups, familiar individuals interact repeatedly, making social experience an important potential mediator of behavior. Early-life experience with social status dictates whether L. dalli juveniles initially sexually differentiate as male or female, as well as the speed of reproductive development. Independent of early-life social status, however, all young adults successfully integrate into novel adult social groups. As an adult, status experience has transient effects on agonistic behavior but not status outcome in a contest, which is influenced by physical condition. Together, these studies provide a comprehensive look at the social, reproductive, and neuroendocrine factors associated with individual variation in agonistic behavior and empirically-based predictions about the fitness consequences.

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