flashing simultaneously like synchronized Christmas lights. Scenes like this really happen every summer in the Great Smoky Mountains, home to the firefly species. Individual males fly around flashing a species-specific pattern, trying to draw response flashes from females. But what makesunique is that they flash in unison with their peers, rhythmically lighting up the entire fields.

For years, scientists have been left to guess as to the specific reason the bugs synchronize their illumination. But now, thanks to research described in the journal Science, researchers have shown that female P. carolinus respond at a much higher rate to synchronized flash patterns compared to those that are asynchronous, indicating that the synchrony plays an important role in helping females locate their potential mate.

Study authors Andrew Moiseff, a professor of physiology and neurobiology at the University of Connecticut, and Jonathan Copeland, a professor of biology at Georgia Southern University, have been studying synchrony in male P. carolinus since the early 1990s. But this is the first time they've designed an experiment that directly probes the effect's underlying behavioral purpose. "We've looked at it, and we've described it—all of those sorts of things," Moiseff says, "but we really wanted to understand more about whether or not it served a function."

Several theories suggest that synchrony evolved to facilitate male-female interaction. But none of these have been thoroughly tested, Moiseff says, so he and Copeland tested the responses of six females in a "virtual environment" containing eight light-emitting diodes (LEDs) that simulated the flash patterns of eight separate males.

The researchers used a computer program to vary the degree of synchrony between the LED flashes and measured the responses of individual females to four different stimuli ranging from unison synchrony to completely asynchronous. They found that, on average, females responded to 82 percent of the stimuli that resembled males lighting up in unison, and responded to a similarly high percentage of a "near-unison" pattern. By contrast, they responded very little to completely asynchronous flashes.

While the result indicates that males flash in unison to influence female behavior, just how females process this information was still unclear. The researchers tackled this question by observing females' response when seven of the eight diodes were hidden. When a female detected and focused on the P. carolinus flash pattern from a single virtual male, she would respond accordingly with a flash of her own. But when all eight—including the one to which she had previously responded—were flashing asynchronously, her responses decreased. "That suggested that for some reason she was not attending to a single diode. She was somehow looking at all of the diodes (at the same time), and attending to a much greater visual field," Moiseff says.

This makes sense, according to the researchers, if one considers that the male firefly will be flying as he flashes—potentially covering a large space. "If a female processed only flashes from a restricted spacial area," it says in the paper, "she might miss some of the male's flashes as he changed location," and fail to recognize his species-specific pattern.

Still, while this strategy would seem to help a female locate a single flying male, it would also seem to be a hindrance when multiple males are flashing in her field of vision. Moiseff and Copeland propose that synchrony "may be the behavioral solution to this problem," since it would maintain the clarity of the specific pattern the female recognizes.

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