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  June 23, 2003

Neurobiologist Unraveling Mysteries OF Fireflies' Flash

They perform in unison, but have never rehearsed.

For three weeks each June in the Great Smoky Mountains National Park, groups of hundreds of fireflies flash their tiny lights on and off simultaneously in the evening darkness. Just how and why their behavior is so perfectly synchronized is a mystery UConn biologist Andrew Moiseff is trying to explain.

Image: Andrew Moiseff in his lab.

Andrew Moiseff, professor of physiology and neurobiology, in his lab. Moiseff uses his expertise in electronics and circuitry to simulate fireflies' flashes for analysis under lab conditions.

Photo by Dollie Harvey

Every year, Moiseff, a professor of physiology and neurobiology, heads to Elkmont, Tenn., within the protected confines of the national park, to study the fireflies and record the performance of these miniature beacons of light.

"You have one shot per season," he says.

The rest of the year, Moiseff, who specializes in signal processing - the biological methods by which creatures decipher sensory stimuli - uses his expertise with electronics and circuitry to analyze the flashes under lab conditions.

Moiseff first studied fireflies as an undergraduate at SUNY-Stony Brook in the early 1970s. He joined the UConn faculty in 1983. But it was not until the 1990s that he and a colleague, Jonathan Copeland of Georgia Southern University, began investigating reports of synchronous fireflies in the Great Smokies.

During the breeding season in June, groups of hundreds of male fireflies of the species Photinus carolinus fly above the ground for about two hours each evening looking for mates. As they fly, they emit tiny bright flashes in unison. They wink their lights in bursts of four to eight at a rate of two flashes per second, then pause for up to 10 seconds, stopping simultaneously.

The fireflies synchronize their performance with such precision that Moiseff speculates some form of counting may be involved - a trigger that is activated, perhaps, as the effect of the flash builds up over time. It's a hypothesis he has yet to test.

During the interval, the females of the species - which are far fewer in number - respond from the ground below with flashes that are dim but still clearly visible.

Image: Firefly

Male Photinus carolinus.

Photo by Andrew Moiseff

Naturally occurring synchrony is rare, and synchronous fireflies - first recorded in Southeast Asia - were once thought to be solely an Asian phenomenon. Although the synchrony is obvious within minutes to a casual observer of the Elkmont fireflies, the first task faced by Moiseff and Copeland as scientists was to verify that the flashes were indeed synchronous.

In some species - certain species of frogs, for example - what appears to be synchrony is incidental: as the frogs compete with each other by calling faster and faster, the separate sounds blur into one another and seem to be temporarily synchronized.

To document that the Elkmont fireflies were truly synchronized, the researchers used special equipment - infrared video and electronic photo multiplier tubes with extremely sensitive light sensors. At 33 milliseconds per frame, regular video, says Moiseff, is too slow to make accurate time measurements.

He says studying synchronous flashing in fireflies can contribute to the understanding of how the insect nervous system processes complex communication signals. "Synchronous flashing is an excellent model system to study how communication takes place," he says.

"In order to study how the brain processes sensory information, you need to know what information is being transmitted so that you can use this knowledge in an experimental context," he notes. "The firefly has a simple code - flashes of light that can be adjusted to infinite precision - so you can make a normal or abnormal flash. If the behavior is different for different types of flash, the brain has to be processing them differently."

Moiseff's lab is full of gadgets, including an array of computers, some specially programmed to simulate firefly flashes.

Under lab conditions, using a green light-emitting diode as an artificial male, Moiseff found that a male firefly in a petri dish will synchronize with the simulated flash, suggesting that the synchrony is triggered only by light, not by behavior.

Next, he established that the bugs can't synchronize unless they can see each other. Isolating a male firefly in a 50-gallon garbage can quickly proved that the male firefly does not flash in isolation. Under natural conditions, if two fireflies are separated by mounds and bushes that block their line of sight, they don't flash together, but a third flying above the obstacle, that can be seen by both, may serve as a 'bridge,' allowing all three to synchronize.

Moiseff says there are a number of different theories as to why this species of firefly flashes in unison. Some suggest that synchrony is a form of cooperation; others depict it as a form of competition.

Moiseff doesn't commit to either theory, but says synchrony may be connected to the density of the Photinus carolinus population. The males are not stationary when they flash, he points out, yet the females need to detect a certain rhythm of flashing to identify a potential mate of the same species. In the Smoky Mountains, there are so many male fireflies on the wing at the same time that if they all flashed randomly, it would be hard for the females to detect the rhythm.

This year, Moiseff plans to study the flashing of female fireflies. He recently constructed a small microcomputer system with a tiny green diode that is programmed to flash like an artificial female firefly in a series of pairs he calls "doublet" flashes. With the device - which consists of a tiny keyboard and a couple of penlight cells assembled in an orange case - he says he can "systematically change what the make-believe female does," by increasing the duration of the flashes or the length of time between the doublets. He will use it this summer to explore the patterns and significance of the female fireflies' response.