Next time you tell someone "I love you" or "Hey, that's my parking space," thank a fish. The brain wiring that enables vertebrates like us to vocalize probably first evolved in fish some 400 million years ago, a new study suggests.
Fish can be noisy. They hum, grunt, buzz, and even warble to attract mates or stake out territory. Charles Darwin speculated that fish might have passed on their soundmaking machinery to their vertebrate descendants, including us. But researchers had few clues about how a passionate opera solo might have evolved from an underwater growl.
Now, some insight is coming from a homely fish that likes to lay its eggs while swimming upside down. The midshipman--also called the humming toadfish--is a bottom-dweller found along North America's rocky Pacific coasts. Males carve out cavelike nests under rocks, then perform hours-long humming concerts to lure in females, which lay their eggs on the roofs of the caves. They defend their nests against other males with growls and grunts.
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Andrew Bass, a neurobiologist at Cornell University, has been studying the midshipman's vocal habits for more than a decade. Recently, he and two colleagues mapped out the neural circuitry that controls the fish's soundmaking. They found that a set of rhythmically firing neurons control the fish's vocal muscles and the pitch and duration of its calls. And by tracking the brain development of larval fish, they discovered that the neurons grow at the base of the hindbrain and the upper part of the spinal cord.
That vocal circuitry is remarkably similar in location and function to brain structures found in other vertebrates that vocalize, including birds, amphibians, and mammals, Bass and his colleagues report in tomorrow's issue of Science. The similarity suggests that the vocal structure originally evolved in the common ancestor of modern vertebrates, the authors write, and then spread far and wide.
The finding "makes total sense; it's a lovely piece of work," says Arthur Popper, a biologist who studies fish communication at the University of Maryland, College Park. He says many biologists already think that "the basic structures for hearing evolved in fish, so why shouldn't the structures for sound production have as well?"