This plant uses explosives to remove rival pollens from pollinators

Because plants lack muscular or skeleton structures, their locomotion is limited to one place. Therefore, plants, especially flowering plants, rely on natural forces like wind or pollinating agents like bees and birds.

As flowers produce way more significant numbers of pollen grains than ovules, pollen grains of rival plants compete with one another for space on pollinators. As the pollinator arriving at the flower may already be covered with the pollen grains of rival plants, it influences whose pollen will make it to the next flower.

According to the study published in The American Naturalist, a few plants may have developed mechanisms that eradicate rival pollens and deposit their fresh grains on the pollinating agent. For instance, Hypenea macrantha, a deeply red flower endemic to Brazil, has a catapult-like mechanism that effectively removes pollen from rival flowers.

Until now, researchers thought that this catapult mainly aided in getting a lot of pollen onto the bird’s beak. However, a recent study by researchers at Stellenbosch University captured slow-motion video footage, showing how the catapult-like mechanism effectively removes pollen of rival flowers from the bill of a hummingbird skull and securely places its own pollen on the same spot.

Researchers experimented with depositing pollen grains on the beak of a hummingbird and counting them. Later, the beak was inserted into a Hypenea macrantha flower, which used explosive pollen placement to deposit its own pollens. After this flinging, researchers counted the pollen grains and found a larger number of Hypenea macrantha grains on the beak.

“Flowers visited by hummingbirds deposit their pollen on the hummingbird bills, but there is very little place for the pollen to be deposited. Flowers have evolved a catapult mechanism where pollen is shot at the bill of the hummingbird. The force of the ballistic grains dislodges previously deposited grains from rival plants allowing the flower to place its own grains onto a cleaner bill, thus increasing its chances of reproductive success.: said Prof. Bruce Anderson.

Such mechanisms were considered absent in the plant kingdom, until now. This is the first study to furnish evidence for the idea of male-male pollen grain competition in plants. This competition might have contributed to the evolution of this trait.

“Until recently, no one has ever thought of looking for these kinds of structures in plants. For one thing, the flowers of one individual never interact directly with the flowers of another individual when mating occurs. This makes it hard for flowers to manipulate the male gametes of other flowers as animals can do. This mechanism may actually displace pollen from previous flowers, enhancing male reproductive success by increasing competition for space on the pollinators’ bodies,” Prof. Anderson explains.

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Journal Reference

1. Anderson, B., Sabino-Oliveira, A. C., Matallana-Puerto, C. A., Arvelos, C. A., Novaes, C. S., Calaça, C., Schulze-Albuquerque, I., Santos Pereira, J. P., Borges, J. O., Consorte, P. M., Medina-Benavides, S., Andrade, O., Monteiro, T. R., Marcelo, V. G., D. Silva, V. H., & Oliveira, P. E. (2024). Pollen Wars: Explosive Pollination Removes Pollen Deposited from Previously Visited Flowers. The American Naturalist. DOI: 10.1086/732797