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Science: New Research Traces Human Vocalization to the Venerable Toadfish
A sequence of three movies, narrated by Dr. Bass, illustrating the different types of calls that type 1 male midshipman fish make when nesting. Females and type II "sneaker" males also make calls in other contexts, but these aren't shown here. Midshipman fish are nocturnally active, so these movies were made using an infrared video camera.
[Videos courtesy of Andrew Bass and Margaret A. Marchaterre, Cornell University]
Scowls perpetually, communicates with grunts and growls, spends lots of effort attracting mates and defending territory—no, it's not the human teenager, it's the toadfish.
These noisy creatures share the ability to vocalize with many other animals, from birds, to frogs, to humans. A study in the 18 July issue of Science suggests that the brain machinery that drives vocalization is extremely primitive, having evolved more than 400 million years ago, with the evolution of bony fish. This group contains all fish with skeletons made of bone, instead of cartilage, and it includes the ancestors of all vertebrates.
Toadfish and their close relatives the midshipman fish use an air-filled sac called a swim bladder and the muscles attached to it to make a variety of sounds, such as grunts, growls and hums, to attract mates and defend territories. A brain circuit of rhythmically firing "pacemaker" neurons determines the contraction rate of the vocal muscles and, in turn, the pitch and duration of the fishes' calls.
Andrew Bass of the Department of Neurobiology and Behavior at Cornell University and his colleagues Ed Gilland at Howard University and Robert Baker at New York University mapped this neuronal network in larval toadfish and found that it develops across a specific region that includes the base of the hindbrain and the upper spinal cord.
This pattern of neuronal development is similar to those of other vocalizing vertebrates, suggesting that the brain circuitry driving vocalization may have its origins far back in the evolution of bony vertebrates.
Toadfish belong to one of the two main groups of bony fish, the Actinopterygii, which includes the ray-finned fish. The other group, the Sarcopterygii, includes the lobe-finned fish and the ancestor to modern-day terrestrial vertebrates. Because both groups now appear to share a common compartment in the developing brain, which forms the pacemaker for vocalization, the new findings suggests that this pacemaker evolved before the two groups diverged.
Other aspects of the various vocal systems, namely the vocal organs—such as the swim bladder in fish, the syrinx in birds, and the larynx in mammals—seem to have evolved independently in different lineages, Bass said.
17 July 2008