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Firefly Flashes
Introduction
In the animal world, males show off their studliness to potential mates in courtship displays. For instance, peacocks fan out their feathers for the ladies, songbirds serenade females with their best tunes, and humans cruise around town in sports cars. In this Science Update, you'll hear how male fireflies brag about what they've got.
Podcast
Firefly Flashes
Transcript
A firefly's flashy pickup line. I'm Bob Hirshon and this is Science Update.
In a sort of insect version of a single's bar, male fireflies send out their best flashes in hopes of attracting a mate. Now, scientists have translated exactly what they're trying to say to their female love interests.
Tufts University biologist Sara Lewis and a colleague, Chris Cratsley, found that a firefly's flash advertises its ability to produce good offspring. Lewis says they made this discovery while studying a species called Photinus ignites.
Lewis:
And they're the fireflies that are most common flashing in the early evening. And they generally flash pretty close to the ground.
The researchers measured minute differences in the length of the fireflies' flashes. They found that males with the longest flashes had the best resources for fertilizing a female's eggs.
The researchers then tested whether females actually chose males based on the length of their flash.
Lewis:
Females consistently preferred artificial flashes that were slightly longer in duration than the shorter flashes that he presented to females.
So, female fireflies can tell which suitors have the best reproductive assets by gauging the male's ability to brag about them. For the American Association for the Advancement of Science, I'm Bob Hirshon.
Making Sense of the Research
Humans are relatively unusual animals, in that human females (at least in Western cultures) tend to decorate themselves more elaborately than males do. In most animals, the males have all the fancy accessories: a lion's mane, a deer's antlers, a peacock's feathers.
Why are all these guys so image-conscious? The answer has to do with the economics of mating. Simply put, sperm are "cheap" to make, while eggs are "expensive." Males produce sperm by the millions, but females generally produce limited quantities of eggs. What's more, the eggs require more care once they're fertilized, both inside and outside the body. And in many animal species, the females do most of the work caring for the young after they're born.
The least a female can ask in return is that the male will be a good provider for her offspring. The providing can take many forms. Maybe the male will go out and hunt down food for the female and her young. Maybe the male "provides" good genes to her offspring that will make them more fit for survival. Maybe the male can offer other essential goods and services. (For example, female penguins have been known to trade mating opportunities for stones, which they use to build their nests.)
In the case of the firefly, the male's "gift" to the female comes in the form of proteins that are packaged along with his sperm that help nourish the female's eggs. (Hey, it's not a five-bedroom beach house, but when you're a firefly, you take what you can get.) To advertise that he's got the goods, the male firefly flashes to the female, who flashes back flirtatiously until the mating gets underway.
The researchers first demonstrated that females preferred males whose flashes lasted longer. The difference is barely noticeable to humans, but apparently it's a big deal to female fireflies. They demonstrated this by creating computerized, artificial flashes that mimicked the male firefly's flashes. By using artificial flashes, the researchers were able to strictly control the length of the flash in each experimental trial.
Next, the researchers studied fireflies in the field during mating season, and brought them back to the lab. They separated the long-flashing males from the shorter-flashing males, and mated each to different females (who weren't given a choice of mate). They found that the longer-flashing males were, in fact, passing on a richer protein package to their female mates.
What the study hasn't answered is why the male fireflies are so honest about their assets. It makes sense that the males with better reproductive proteins would want to advertise that with longer flashes, but wouldn't the less-endowed males eventually get wise and try to sustain their flash just a little bit longer? It's certainly possible that the ability to flash longer is somehow tied, biologically, to the ability to make reproductive proteins, but what that relationship is remains to be discovered.
Now try and answer these questions:
- What does a longer flash signify in firefly mating?
- What is the benefit for females in mating with males who flash longer?
- What other traits might be desirable in male fireflies? What would the female want to pass on to her offspring?
- Suppose male fireflies with smaller protein packages started to flash for longer durations. What would happen to this system?
Going Further
The Mating Game, by Discovery.com, looks at courtship rituals across the animal kingdom.
Pulse of the Planet, another radio show, has done many stories on animal mating behavior, including features on:
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