Testosterone alters electric fish’s ability to ignore their own signals

During the rainy breeding season, electric fish engage in a unique underwater “conversation” that undergoes a transformation. Male fish, driven by the desire to find a suitable mate, emit slightly different electric signals to announce their presence and identify potential compatible partners.

A recent study conducted by researchers from Washington University in St. Louis sheds new light on this intriguing phenomenon. The study, authored by biologists Matasaburo Fukutomi and Bruce Carlson from the Arts & Sciences department, and published in Current Biology, highlights the role of the hormone testosterone in shaping the behavior of male electric fish during the breeding season.

The researchers discovered that testosterone, a hormone responsible for various physiological changes in animals, not only prompts male electric fish to elongate the electric pulses they emit during breeding but also influences a crucial brain system in these fish. This brain mechanism allows the fish to disregard their own electric signals temporarily, enabling them to prioritize and respond to signals from other fish, particularly potential mates.

This brain mechanism is known as “corollary discharge,” and it plays a significant role in ensuring that animals can distinguish between their own signals and external stimuli from others. Accurate interpretation and response to external signals are vital for successful reproduction and survival in the animal kingdom.

Electric fish, specifically a type known as mormyrids, emit electric pulses as a form of communication. Interestingly, they have developed a mechanism to effectively ignore or “block” their own electric messages. The corollary discharge system temporarily dampens the fish’s sensory perception immediately after emitting an electric pulse. This momentary inhibition allows the fish to prioritize incoming signals from other fish, enhancing their ability to detect potential mates or relevant information.

Previous studies had established that testosterone treatment affects the electric organs in mormyrids, leading to behavioral changes such as the elongation of male fish signals. However, the recent research by Fukutomi and Carlson goes a step further by revealing how hormone treatment also orchestrates changes in the fish’s signal perception.

In essence, the study focuses on the precise control of timing. Testosterone appears to regulate the timing of corollary discharge, ensuring that the fish continue to disregard their own electric signals at the right moments. This adjustment contributes to the fish’s ability to accurately interpret and respond to external signals, ultimately facilitating successful communication and mating behavior.

Matasaburo Fukutomi, the first author of the study and a postdoctoral fellow in biology, explains, “Testosterone adjusts corollary discharge timing in order to continue ignoring self-generated behavior.” He adds, “Circulating testosterone independently regulates the behavioral output of the electric organ and the corollary discharge that predicts the sensory consequences of that behavior.”

Looking ahead, Fukutomi and Carlson anticipate that their findings will pave the way for further exploration into the intricate mechanisms through which testosterone influences the behavior and perception of electric fish. This research could potentially unveil insights into how hormones impact neural circuits at the cellular level, contributing to our understanding of the relationship between hormones and behavior.

Additionally, the study raises intriguing questions about whether similar mechanisms are involved in both seasonal changes and evolutionary adaptations in electric fish behavior. Exploring these questions could provide valuable insights into the ways in which hormones shape animal behavior and the underlying neural processes.

Professor Bruce Carlson emphasizes the significance of this research, stating, “Early pioneering studies in this system paved the way toward better understanding of corollary discharge across animals, including humans, and this system continues to shed new light on corollary discharge function.”

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