Context-Specific Sound Production Responses to Environmental Manipulation in the Vocal Reef Fish Rhinecanthus rectangulus

Abstract

Communication between individuals of a species can reduce social disorder, allow for more efficient cohabitation and enhance individual fitness. Many species have evolved complex chemical signals, vocal signals, or action patterns that convey an intent to attack, intent to mate, or submissiveness which allow each individual to adjust their behaviors to maintain access to the benefits of group living. Even solitary organisms form communicative signals in order to find, attract, and secure a mate. Every lineage of vertebrate and many invertebrates such as arthropods, cephalopods, and gastropods have formed unique communicative signals that convey some meaning to conspecifics. Characterization of communicative signals in natural contexts allows researchers to interpret the internal state of both the senders and the receivers based on the information being exchanged.

Sound production is the form of communication that this thesis will focus on. It is not the most common form of communication, but it is the form with which humans are most familiar. Vocal signals have evolved in both vertebrates and invertebrates (arthropods), and are produced by several different mechanisms. While most mammals, amphibians, and birds vocalize by the forced flow of a medium through a small orifice to create vocal signals, fish exhibit a variety of mechanisms. This allows for the generation of many different experiments based on the topic.

This thesis is based on the central question: why do some fish produce multiple vocalization types? This thesis’s species of interest, the triggerfish Rhinecanthus rectangulus, appears to have evolved multiple mechanisms for the generation of different vocalization types. While the mechanisms of R. rectangulus vocalization are not directly explored in this thesis, this work builds on previous research that addressed the sound production mechanisms for triggerfishes and closely related species. The production of different sound types via different mechanisms indicates that different sound types are highly adaptive in this fish lineage and contribute to fitness. R. rectangulus and a common reef predator, the piscivorous moray eel Gymnothorax undulatus, will be the focus of this research.

The first chapter of this thesis provides background information on animal communication, aquatic sound production, and the focal species R. rectangulus. The second chapter examines the conditions in which different sound types are produced: are the sound types context specific? This will be determined when call rates of different sound types in the presence of different stimuli (conspecific territory intruders, model conspecifics, predators, and no intrusion) are quantified. It will also be determined if sound types are used differentially in one context over others. The third chapter will briefly examine the neuroanatomy of the triggerfish brain, specifically the habenula which is a region that may be responsible for higher processing of signals produced by conspecifics in agonistic interactions.