H. macrantha Flowers have both male and female reproductive organs. To avoid mating with themselves, individual flowers go through a male and then a female phase. They rely on hummingbirds to transfer pollen between flowers, rewarding them with sweet nectar (SN: 02/03/15). When a hummingbird visits a flower in the male phase, its beak triggers a catapult-like mechanism that projects all the pollen from a compartment enclosed by a petal in a single burst. Then the flower becomes female.
To see if the sprayed pollen outweighed the competition, evolutionary ecologist Bruce Anderson and his colleagues simulated a hummingbird visit by sticking a hummingbird skull into flowers. They marked the pollen with tiny fluorescent particles, then applied the fluorescent pollen to the part of the beak where pollen tends to accumulate. They then inserted the beak with its fluorescent pollen load into a new set of male and female flowers and tracked where the marked and unmarked pollen particles ended up landing.
Hummingbirds’ beaks shed twice as much fluorescent pollen when they were stuck in exploding males as when they were stuck in inert flowers that had already exploded. What’s more, the more fluorescent pollen an explosion removed, the more successful it was at depositing pollen from the flower onto the beak. High-speed video showed that the pollen grains from the exploding flowers acted like missiles to knock off existing pollen.
“It’s almost like there’s a division of labor for pollen. Some of it goes to mating, and some of it goes to fighting,” says Anderson, of Stellenbosch University in South Africa. More research is needed, he says, to determine whether pollen bursts result in more offspring for male flowers.
The animal world is full of males trying to get rid of their rivals’ sperm and replace it with their own (SN: 09/04/14). For example, many animal penises have elaborate shapes to retrieve sperm from females’ reproductive tracts. Even the hooded shape of the human penis may have evolved to extract sperm from other men, as evolutionary psychologist Rebecca Burch and her colleagues have shown. This is the first experimental evidence of a similar sperm-extraction strategy in plants.
“Plants are not just stationary objects,” says Burch, of the State University of New York at Oswego. “They actively communicate, compete, and sabotage the reproduction of other plants.”
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