Fish hum, grunt, and growl to get their message across

It’s only a humble hum or an undistinguished grunt or growl. But to a midshipman fish, it’s effective social communication. Hums help the boys get the girls. Grunts and growls warn off would be trespassers.

Scientists have studied animal communication for decades. Now, for the first time, a research team has traced the underlying neurobiology that makes the fish talk possible.

It’s an early step in an emerging research field that seeks insight into the evolution of behavior from the perspective of neurobiology. In recent years, visiting scientists have pursued this quest at the Marine Biological Laboratory (MBL) in Woods Hole, Mass. Last week, MBL reported the results of work by Andrew Bass of Cornell University, Edwin Gilland of Howard University, and Robert Baker of New York University.

According to MBL, the researchers have shown “that the sophisticated neural circuitry that midshipman [fish] use to vocalize develops in a similar region of the central nervous system as the circuitry that allows a human to laugh or a frog to croak.”

The research team also published technical details of its work last week in the journal Science. If you want to hear the fishes’ hums, grunts, and growls go to mbl.edu/news and click on the press release about “When fish talk.” It has links to the sound files.

The scientists are after more than an understanding of how the midshipman and its close relative the toadfish can “talk.” Dr. Bass notes that vocal communication probably is widespread among fishes. Fish account for nearly half of vertebrate species living today. The evolution of the neurobiology underlying auditory fish communication sheds light on the evolution of communication skills of the rest of us vertebrates. Also, it gives insight into why fish have been so successful in evolving to make the most of Earth’s changing environments. “We’re only touching the tip of an iceberg here,” Bass says.

There’s more to the neurobiology of vertebrate communication than vocalizing. The right sight, sound, or smell can cue up a wide variety of so-called conditioned responses. Flashing lights cue rats to push levers. And as Kathryn Burke at the University of Maryland and colleagues pointed out last week in Nature, while the sight of McDonald’s golden arches may evoke thoughts of hamburgers, it may also evoke general feelings of hunger or happiness.

Yet familiar as such responses are, the researchers noted that it still “is not known how conditioned reinforcers control human or other animal behavior.” So they went looking for clues in the neurophysiology of rats willing to press levers that delivered no reward. All it took to set them to work was the appropriate light signal. The Nature paper details how the researchers traced the brain circuitry involved. They were able to distinguish when rats reacted in expectation of gaining a general sense of well-being and happiness, and when they expected to get a specific food morsel reward.

Understanding more about the neurobiology underlying human and animal behavior and its evolution should give insight into the age old question of what make humans human. As Bass says, scientists are just touching the tip of a very large iceberg.