Dogs Bark, Birds Chirp, Fish Grunt

Newly hatched midshipman larvae. Image courtesy of Margaret A. Marchaterre, Cornell University

Wednesday, July 23rd, 2008--

The origins of vocal communication may date back to prehistoric fish. Andrew Bass, a neurobiologist at Cornell University in Ithaca, and his colleagues report in the journal Science that vocal communication is tied to an ancient region of the brain--a neural compartment that existed 400 million years ago in the earliest bony fishes.

Fish--like birds, mammals and other vertebrates--make sounds to communicate: male midshipman fish (Porichthys sp) let out what's known as a hum ("it sounds like a drone of bees," Bass says) to attract female fish to their nests; midshipman will also "growl" or "grunt" to defend their territory, says Bass, lead author on the study.

"Probably most non-scientists and scientists as well are not aware that fish are making sounds for the purposes of social communication," Bass says. And fish are not the only under-reported vertebrate vocalizers: crocodiles, for example, also vocalize. A recent study suggests that unhatched crocs may grunt in the egg to synchronize hatching of the clutch and signal to their mama crocodile when she should start digging them out of the sand.

Bass says the question he and his colleagues wondered was: "what are the evolutionary origins not only of those behaviors, but of the parts of the nervous system that are used to produce [the vocalizations]?"

To find out, the researchers stained neurons in the brains of larval fish with fluorescent dye and watched their neural circuitry develop. The researchers found that the bundle of neurons involved in vocalization is located in an ancient compartment between the tail end of the brain and the front end of the spinal cord.

Not only is this neuronal network old--it's been conserved throughout evolution, Bass says. His research suggests that the same compartment of the brain is used by all vertebrates during vocalization. This means that fish, crocodiles and humans are tapping into a similar bundle of neurons when we growl, grunt and speak.

--Flora Lichtman