Dissertations, Theses, and Capstone Projects

Date of Degree

9-2017

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Paul M. Forlano

Committee Members

Christopher B. Braun

Thomas Preuss

Andrew H. Bass

Joseph A. Sisneros

Subject Categories

Behavioral Neurobiology | Integrative Biology | Molecular and Cellular Neuroscience | Systems Neuroscience

Keywords

alternative reproductive tactics, dopamine, neurochemistry, noradrenaline, social behavior, teleost

Abstract

The plainfin midshipman fish, Porichthys notatus, provides an excellent opportunity for delimiting the influence of neurochemical content on vertebrate vocal behavior, in part because the production and recognition of social-acoustic signals is vital to their reproductive behavior. There are two distinct reproductive male morphs that follow divergent developmental trajectories with corresponding alternative reproductive tactics: type I males are the territorial/nesting morph that vocally court females during the summer breeding season while type II males do not court females, but instead sneak spawn in competition with type I males. Catecholaminergic neurons, which synthesize and release the neurotransmitters dopamine or noradrenaline, are well-established modulators of various motivated vertebrate sociosexual behaviors, including intraspecific vocal communication. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine synthesis, and TH immunoreactivity (-ir) can be utilized to demarcate neurons in the brain that produce and release dopamine and noradrenaline. Key components of the sexually polymorphic neural circuitry essential to midshipman vocal-acoustic behavior express robust TH-ir innervation, overlap with the social behavior network, and are conserved (in part) across vertebrate taxa.

The primary goal of this work was to determine if differential distribution and activation of catecholamines in the brain serve as a substrate for variation in alternative reproductive tactics and vocal behavior between type I and type II male midshipman. Firstly, an intrasexual morphometric comparison of TH-ir neuron number and fiber density revealed that type II males had a greater TH-ir innervation within and in close proximity to the hindbrain vocal pattern generator. Secondly, using the immediate early gene protein cFos as a proxy for neural activation, it was found that two forebrain dopaminergic nuclei were more active in type II males that were exposed to playbacks of conspecific hums compared to ambient noise. Thirdly, cFos-ir induction within diencephalic dopaminergic neurons and brainstem noradrenergic neurons shared positive relationships with the total amount of time type I males spent humming. Furthermore, it was found that exposure to acoustic stimuli with different valences (hums, grunts, or ambient noise) as well as divergent states of calling behavior (humming versus non-humming) evoked contrastive shifts in functional connectivity among TH-ir and social behavior network nuclei. Taken together, this work provides cogent evidence that the differential distribution and activation of catecholaminergic neurons may contribute to both processing of social-acoustic signals and divergent intrasexual behavior expressed as alternative reproductive tactics in midshipman fish.

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