The Plainfin Midshipman

Three midshipman in a nest. From left to right: type II male, type I male, female

Three midshipman in a nest. From left to right: type II male, type I male, female

We primarily use the plainfin midshipman (Porichthys notatus), along with other closely related toadfish species, as a model system to study the neural and hormonal mechanisms of acoustic communication in social contexts. Midshipman fish breed during the summer months on the rocky shorelines of the western United States. They have three sexual morphotypes. In addition to females, there are two kinds of male in this species: territorial, nest-building type I males that excavate nests and court females, and smaller ‘sneaker’ type II males that mimic female appearance and mate exclusively by stealing fertilizations at the nests of type I males. Vocalizations are a critical component of the breeding system in these fish, and are produced by rapid vibrations of a muscularized, air-filled swim bladder driven by the output of a vocal pattern generating circuit located in the brainstem. Fish of all morphotypes are capable of producing vocalizations, but the largest vocal repertoires belong to type I males, who both acoustically court females and participate in territorial agonistic interactions that include vocal components. Type II (sneaker) males and females have a restricted vocal repertoire that is used solely in agonistic interactions. The divergence in behavioral phenotypes is mirrored by differences in both circulating steroids and in hormone effects on the patterning of vocal-motor output. Dramatic vocal behaviors, along with distinct hormonal phenotypes of each reproductive morph make the midshipman an excellent model system for studying the neural and endocrine control of acoustic communication.

Evolution of Social Signaling Circuits

Communication through sound production is strikingly widespread throughout the animal kingdom, especially within vertebrates. Therefore the question arises: did vocalization evolve only once or multiple times within vertebrates? As evolutionary neurobiologists, we seek to answer this question by investigating the organization of brain circuits responsible for vocal behavior. We use neural tracing, immunocytochemistry, and in situ hybridization to identify specific neural populations relevant to vocalization, and RNA-sequencing and quantitative PCR to characterize gene expression profiles within and across vocal motor systems. These studies will allow us to determine whether vocal fishes share a core set of neural characters with other vocal vertebrates, and whether the circuits share developmental and evolutionary origins across species. 

Neurohormonal Mechanisms of Social Signaling

In many vertebrates, including fish, vocalizations are inextricably tied to the expression of social and reproductive states, and as such influenced by hormones that regulate a host of related behaviors and physiology. A large part of hormonal action is devoted to coordinating reproduction, including courtship vocal behavior, to the appropriate times of the annual and daily cycle. Our lab investigates how conserved hormones, such as steroids and neuropeptides, orchestrate the expression of vocalization in the plainfin midshipman fish. To do so, we use in-vivo neurophysiology combined with pharmacology to examine hormone effects on neural output controlling vocalization. We also use molecular techniques to quantify and locate hormone receptor expression in the brain. Finally, we observe vocal behavior in natural and semi-natural field and captive environments to probe hormone control of spontaneously occurring vocal behavior.

Mechanisms of Acoustic Communication

We are interested in understanding the neural basis of acoustic communication. Midshipman and other toadfish make ideal model systems to answer this question, because their vocalizations are generated by only a single pair of muscles driven by a relatively simple and well characterized hindbrain central pattern generator. The midshipman vocal pattern generator is extreme in its ability to produce a highly synchronous and long-lasting output, providing an exaggerated phenotype that is easily measured and manipulated. Furthermore, they show remarkable seasonal plasticity in the auditory system that encodes vocalizations, which can be leveraged to understand mechanisms underlying tuning in the vertebrate ear. Using these factors to our advantage, we are able to investigate the neural and hormonal mechanisms driving toadfish vocalization and hearing. Neurophysiological and pharmacological studies allow us to manipulate these circuits to understand the cellular and network properties that allow for the remarkable behavior of these fish. We also investigate natural variation in vocal-motor and auditory circuits, including sex differences and changes across daily and seasonal timescales, to identify characters that are fundamental to acoustic communication.