This deceptive South African daisy builds a fake fly to trick male flies into pollinating it

Male flies in South Africa are being taken for a ride by a species of South African daisy, Gorteria diffusa, which have evolved to produce a complicated structure resembling a female fly on their petals.

The fake flies give the daisies an evolutionary advantage by attracting more male flies for pollination; they land on what they think is a female fly, try to mate, deposit pollen while they’re rooting about, and eventually give up and take off.

These fraudulent flowers are the only daisy known to make such a convincingly phony fly – with three dimensional hairy bumps and white highlights to complete the look. But until now, the mechanism behind how they do it has eluded scientists, until now.

There are three sets of genes involved, according to a new study in Current Biology. All three sets already have other functions in the plant: one moves iron around, one makes root hairs grow, and one controls when flowers are made.

A male fly approaches a flower, lands on top of what he thinks is a female fly, and jiggles around. He’s trying to mate, but it isn’t quite working. He has another go. Eventually he gives up and buzzes off, unsuccessful. The plant, meanwhile, has got what it wanted: pollen. Credit: R. Kellenberger/University of Cambridge

“This daisy didn’t evolve a new ‘make a fly’ gene. Instead, it did something even cleverer – it brought together existing genes, which already do other things in different parts of the plant, to make a complicated spot on the petals that deceives male flies,” explains senior author Beverley Glover, Professor in the Department of Plant Sciences and Director of the Botanic Garden at the University of Cambridge in the UK.

The iron homeostasis genes add more iron to the petal – turning its normally reddish-purple pigments into a more fly-like blue-green hue. The root hair gene (GdEXPA7) result in enlarged papillate petal epidermal cells, giving it a bumpy fly texture. And the third set of genes make the fake flies appear in apparently random positions on the petals.

A microscope image of the fake fly region on the petal.
A microscope image of the fake fly region on the petal. Credit: University of Cambridge

This is a mechanism called “gene co-option” and it’s important in the evolution of novel biological forms. The researchers were even able to work out the order that the fake flies came into being on the plant’s petals: colour first, then random positioning, then texture.

The group of plants including this deceptive daisy is very young in evolutionary terms at only 1.5 to 2 million years old, and because the earliest daisies of this family didn’t have the fake fly spots, it means they must have appeared on the daisy petals very rapidly.

Read more: Fake sex pheromones deceive male wasps.

“We’d expect that something as complex as a fake fly would take a long time to evolve, involving lots of genes and lots of mutations. But actually, by bringing together three existing sets of genes it has happened much more quickly,” says Dr Roman Kellenberger, a postdoctoral researcher at Cambridge and first author of the study.

16 different types of gorteria daisy flowers with differing shades of petals and fake fly spots
Different types of Gorteria have different spot variations. Credit: A. Ellis

To figure all of this out, the team compared which genes were switched on in petals with and without fake flies in the same type of daisy, and compared these genes to ones in petals from a different type of daisy that produces a simple spot pattern.

“It’s almost like evolving a whole new organ in a very short timeframe. Male flies don’t stay long on flowers with simple spots, but they’re so convinced by these fake flies that they spend extra time trying to mate, and rub off more pollen onto the flower – helping to pollinate it,” says Kellenberger.

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