It's Alive

Dastardly daisies

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3:00pm, August 19, 2013

FAKE OUT  Sitting atop the most flylike of the sexually deceptive daisies, a real fly (right) encounters a sizable dark lump of plant tissue (left) with a complex texture mimicking a female fly.

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This daisy isn’t just any old sex cheat. It can be sexually deceptive three ways and in 3-D. And now a plausible-sounding hypothesis for how such variety in trickery evolves has just been squashed flat.
 
Nicknamed the beetle daisy, South Africa’s Gorteria diffusa blooms in 14 distinct forms, shading from yellow to orange and often marked with black dots once thought to mimic little beetles. But bee flies, Megapalpus capensis, are the insects that the flower actually turns into mating-obsessed fools.
 
“When males are seeking females, they fly around and quickly land on black objects,” says ecologist Marinus de Jager of Stellenbosch University in South Africa. The back of another male fly or a flat dot on a daisy will do. Usually the fly recognizes the ‘oops’ and just flies away. But three forms of the beetle daisy sport raised black dots that inspire “turning and twisting behavior, as well as hopping on the spot and arching the abdomen downwards,” de Jager says. In other words, mating behavior.
 
Such wriggling does wonders for the plant by transferring more pollen onto the bee fly than a simple nectar-sipping visit would do. But mistakenly trying to copulate with a plant doesn’t help the fly. Biologists had never realized that any plants except orchids practiced pollination by sexual deception until the description in 2010 of this devious daisy.
 
The daisy’s variety of deceptive spots might reflect geographic differences in what turns on male bee flies, de Jager and adviser Allan G. Ellis once thought. A survey of male bee fly proclivities, though, doesn’t find much difference from one place to another, the researchers report in the June Evolution. Instead, maybe deception evolved several times through different mutations, de Jager and Ellis now speculate. The variety might arise when the insects get good at learning from dumb mistakes. Jumping the border between life’s kingdoms for sex could be the move of “young, naïve males,” de Jager says. 

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