VCU news

By Sathya Achia Abraham

A new study by an international research team shows for the first time that clownfish populations found in different regions of the Indian Ocean demonstrate diverse calls -- either “chirps” or “pops” -- when defending their territory.

These findings may help researchers better understand the role of sounds in fish behavior and how changes in behavior may lead to the formation of new and distinct species.

Michael L. Fine, Ph.D., a Virginia Commonwealth University Life Sciences biologist studying fish sound production, together with researchers at the University of Liege in Belgium and the Research Center on the Marine and Freshwater Ecosystem in France, are the first to report geographic variation in sounds of a coral-reef fish species. Their findings were published online Friday in The Proceedings of The Royal Society B – Biological Sciences.

“Genes of coral-reef fish can be fairly similar in populations of a species living thousands of miles apart because their eggs can be dispersed widely by strong ocean currents,” said Fine, a professor in the Department of Biology at VCU who helped analyze the recorded fish sounds using computer software. “However, we found that there were differences in the sounds produced in the same species living in the reefs of Madagascar and Indonesia.”

They found a differentiation of agonistic calls produced by the clownfish, Amphiprion akallopisos, from populations in Madagascar and Indonesia – a distance of approximately 4,000 miles.

The research team identified three different sound types in the Madagascar fish and two in the Indonesian group. Results from the sound analyses showed that the Madagascar fish produced “chirps,” and both groups produced two types of pops — “short pops” and “long pops.”

“Our findings provide evidence of differentiation of local populations,” he said. According to Fine, sounds are important in maintaining separation between species, and they tend to change in related animals undergoing speciation. Generally, the pattern generators and anatomy that control sound production are believed to result from genetic instructions.

“In this case, the different sounds that are produced may reflect genetic changes that have occurred because the two fish populations have probably been separated for long periods,” he said.

Fishes make sounds for different reasons, but the two most common types of sounds are made for courtship and agonistic behaviors, said Fine. The differences observed in the agonistic callings of these populations is a complexity not previously recorded in fish acoustic communication.

The team collected fish from the two geographic locations and observed them in a community tank. A sea anemone and clownfish pair were placed in the center of the tank, and after 15 minutes, a second pair of clownfish was introduced to the tank. Sounds were recorded when the fish defended its sea anemone. The sea anemone, which is a home to these fish, possesses stinging cells that protect the clownfish, but can kill other fishes.

Sounds were recorded using a device called a hydrophone. They measured the differences in the number of pulses, pulse duration and dominant frequency in the sounds produced.

“Typically an animal needs to have a territory in order to mate. The sea anemone is a valuable resource to the fish. If another pair wants to invade it, the existing pair does not want to share,” Fine said. “Therefore, sounds were produced by the pair of clownfish when other fishes entered the sea anemone.”

Fine collaborated with Eric Parmentier, Ph.D, assistant professor, and Pierre Vandewalle, Ph.D., professor, both at the University of Liege in Belgium; and Jean-Paul Lagardère, Ph.D., a researcher with the Research Center on the Marine and Freshwater Ecosystem in L’Houmeau, France.