Courtesy of Marcus Stensmyr
The next time you swat a fruit fly in your kitchen, take heart from the fact that people have apparently been struggling with these fly infestations for around 10,000 years.
A study published Thursday Thursday Drosophila melanogaster first shacked up with humans when the insects flew into the elaborately painted caves of ancient people living in southern Africa.
Thursday in the journal Current Biology.
Scientists say the flies would have been following the alluring smell of stored marula fruit, which were collected and stored by cave-dwelling people in Africa. This tasty yellow fruit was to staple in the region in those days.
Humble fruit fly now lives with humans all over the planet and one of the world's most studied creatures. Nobody Prize in Physiology or Medicine has been awarded for research on Drosophila. By Thomas Hunt Morgan of Columbia University, whose research is in the mainstream of genetics.
It has interesting genetics, "explains Thomas Kaufman, a biologist at Indiana University in Bloomington. "We're beautiful." They're beautiful little animals, and we love them. "Seriously."
But with all that love and study, the origins of this fly, and have been a mystery.
"I've been wondering about this for the past 20 years," says Marcus Stensmyr, a biologist at Lund University in Sweden who uses these flies to study the olfactory system. "It's really kind of a life-long ambition, if you wish, to find where they come from."
Scientists have known that, like people, they seem to have started out in Africa – somewhere.
"You find them in your kitchen." You find them in my kitchen – you find them in everyone's kitchen, "says Stensmyr. "But if you go out into the forest, you simply do not find them."
Recently, researchers collected from Africa and looked at their genes. Zambia and Zimbabwe, found that the greatest genetic diversity was found in Zambia and Zimbabwe, suggesting that this species had its start in the southern central region of the continent.
But it was not enough to turn up much of anything.
"After a number of failed excursions down to Africa," says Stensmyr, "we thought, 'OK, so maybe they are associated with some specific fruit in their original home.' "
Stensmyr and his colleagues studied a long list of possible fruits D. melanogaster is known to prefer. The flies favor citrus fruits – like oranges, for example.
Courtesy of Marcus Stensmyr
"We came to a candidate fruit – that was marula fruit," says Stensmyr. The yellow fruit is about the size of a large plum. "It has a sweet and nice taste."
The researchers traveled to the woodlands of the Matobo National Park in Zimbabwe. They found fruiting marula trees and put out traps. Bingo – they caught D. melanogaster.
"We found tons of flies," Stensmyr recalls.
Further study showed that wild D. melanogaster strongly prefer marula fruit over oranges.
What's more, it's commonly used in labs. This strain was established in 1916 from a fly population in Canton, Ohio.
"They actually have retained the preference for marula," says Stensmyr. "They would go for the marula as well."
The researchers isolated one particular chemical in this fruit – ethyl isovalerate – that apparent particularly important. This is not the case, but it is not the same.
This is an intriguing clue for how these insects may have started to make their home with people. Near the animal flies, there are caves where the San tribes once lived. These people left behind are beautiful paintings – as well as the pits of marula fruit that they had eaten. From one cave alone, excavators turned up 24 million marula stones.
"They really, really loved marula," says Stensmyr, who points out that the stones found date from about 12,000 years ago to about 8,000 years ago. "During the times when these caves were inhabited, the San people must have brought enormous quantities of marula into the caves."
That means marula was likely to be stored in the forest. The strong smell of this marula would have attracted the flies.
To test whether or not wild flies would actually enter a cave, the research team put into the fermented marula along the far wall of the Nswatugi cave. Sure enough, over a period of a few days D. melanogaster flies.
It study, has completely delighted other scientists who study fruit flies.
"I'm keen," says Kaufman. "That was inspired." It's really a neat paper. "
"I thought it was fantastic," agrees Celeste Berg, a developmental geneticist at the University of Washington, Seattle, who has used flies in her research for 30 years. "I thought their data was really quite striking."
Berg says she wonders exactly how the flies would have spread from these caves to the rest of the world.
"I think it's exciting to learn about the origins of fruit flies and even if you're not an ecologist or a geneticist, I think it's just natural to be interested in the history of the organism you study," says Berg. "I had not heard that they prefered citrus." I did not even think that they preferred citrus. of. "
Debbie Andrew, a developmental biologist at the Johns Hopkins School of Medicine who has worked with the fruit.
"They built a good story," says Andrew. I like the story. "
She says, "I do not know;
Based on this paper, says Andrew, the old saying, "should fancy like an arrow, and fruit flies like a banana," should really be changed.
"Time flies like an arrow," she says, "and fruit flies like an orange, or a marula fruit, or perhaps an orange spiked with ethyl isovalerate."