The South African daisy uses mimicry to lure flies
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An orange-hued daisy in South Africa has an unusual lure to attract pollinators: a little structure on its petals that resembles a female fly. Male flies descend on the petals in hopes of mating but end up ferrying the flowers’ pollen to other plants. The fake fly-like structure appears to have emerged within the relatively short evolutionary time span of 2 million years, according to scientists who have identified three sets of genes in the daisy that were repurposed to evolve the lure.
Following winter rains each year, South Africa’s Namaqualand desert bursts into glorious bloom for a few short months. The abundance of flowers creates tough competition for South African daisies (Gorteria diffusa), which lure pollinators such as bee flies (Megapalpus capensis) with their false-fly petals.
“The male fly comes in and lands very specifically onto the spot as if they want to mate with it,” says Beverley Glover at the University of Cambridge. In the process of “jiggling around looking confused”, the fly shakes pollen onto itself, which it carries from plant to plant, she says.
To find out which genes are responsible for the flower’s fakery, Glover and her team compared the genes expressed in fake-fly petals with those in regular petals. South African daisies have evolved slightly different-looking fake flies depending on the subpopulation of the species, but most include one to four dark black dots with a raised, hair-like texture that mimics a female fly. Some flowers lack the fake female fly altogether. The researchers also compared South African daisies with other species of daisies that have simple spots and dark rings that lack the detail of false flies.
They found three sets of genes involved in creating the deceptive lure, all of which were already performing other functions in the flower. “[These genes] have all been co-opted or recruited into making this amazing fly mimic,” says Glover. “We know that this particular daisy has evolved to make these spots within the last 1.5 to 2.5 million years.”
A set of genes that move iron around the plant has been co-opted to ferry blueish-black pigments to the petals. The genes that make root hairs, which help the plants absorb nutrients from the soil, also give the fake fly a hair-like texture. The group of genes that tell the plant when to produce flowers makes the fake flies appear on different petals.
The work “contributes to solving one of the major problems in mimicry research”, says Steve Johnson at the University of KwaZulu-Natal in South Africa who wasn’t involved in the work. Specifically, it helps untangle how plants can gradually evolve complex structures through stages of gene copying.
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