A male fly approaches a flower, lands on what it thinks is a female fly, and moves. He is trying to mate but fails. She tries again, and his seductive partner doesn’t respond. There’s nothing to do. Finally, he gives up and leaves without achieving his goal. It is the flower that he has got what he wanted: the pollen.
A South African daisy, widespread gorteria, it is the only one known to have such a complicated structure that its petals resemble a female fly. The mechanism behind this convincing three-dimensional hoax, complete with furry protrusions and white reflections, has intrigued scientists for decades.
Now, the researchers have identified three sets of genes involved in the construction of the false fly on the daisy’s petals. The big surprise is that the three sets already have other functions in the plant: one moves the iron, one makes the root hairs grow, and the other controls when the flowers form.
The study found that the three sets of genes have come together in the daisy’s petals in a new way to build fake flies. ‘Iron move’ genes add iron to the normally reddish-purple pigments of the petal, changing the color to a more fly-like blue-green. Root hair genes cause the hairs to expand on the petal to give texture. And the third set of genes causes the false flies to appear in seemingly random positions on the petals.
With existing genes
“This daisy did not develop a new ‘make a fly’ gene. Instead, he did something even smarter: he brought together existing genes, which already do other things in different parts of the plant, to create a complicated blotch on the petals that fools the male flies,” says Beverley Glover, a professor in the Department of Science. from the University of Cambridge and lead author of the study published in ‘Current Biology’.
The South African daisy produces a convincing false fly on its petals
The researchers say the daisy’s petals give it an evolutionary advantage, attracting more male flies to pollinate it. The plants grow in a harsh desert environment in South Africa, with only a short rainy season in which they produce flowers, are pollinated and set seeds before they die. This creates intense competition to attract pollinators, and the false fly-studded petals make the South African daisy stand out from the crowd.
Compared to most living organisms, the plant group, including the sexually deceptive daisy, is very young in evolutionary terms, between 1.5 and 2 million years old. The first daisies in this family tree did not have the false fly spots, which means they must have appeared on the daisy petals very quickly.
“We would expect something as complex as a fake fly to take a long time to evolve, involving many genes and many mutations. But actually, by bringing together three sets of existing genes, it’s happened much faster,” explains Roman Kellenberger, a postdoctoral researcher in the Department of Plant Sciences at the University of Cambridge and first author of the study.
Researcher shows a flower with a fake female fly
To get their results, the researchers compared which genes were turned on in the petals with and without false flies on the same type of daisy plant. They also compared them to petals from a different type of daisy that produces a simple spotting pattern, to determine which genes were specifically involved in making the daisy’s spots so deceptive.
This is the only example of a flower producing multiple false flies atop its petals. Other members of the daisy family make much simpler spots, for example spots in a ring around all the petals, which are not very convincing to royal flies. By comparing the different daisies in the family tree, the researchers were able to determine the order in which the false flies emerged: first color, then random positioning, then texture.
“It’s almost like growing a whole new organ in a very short period of time. Male flies don’t stay long on single-spotted flowers, but they’re so convinced by these false flies that they spend more time trying to mate and rub more pollen on the flower, which helps pollinate it,” says Kellenberger.