Australasian Science: Australia's authority on science since 1938

Flower Evolution from the Birds to the Bees

 Credit: BirdImages/iStockphoto

Credit: BirdImages/iStockphoto

By Mani Shrestha, Adrian G. Dyer and Martin Burd

Walking around in the Australian bush we can see a dazzling array of different flower colours, but have you ever wondered how and why these evolved?

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Plants face a challenging courtship problem. They can’t walk, talk... or the other pleasant parts that might “go with a date”. So to enable sexual reproduction to enhance the genetic variability of their offspring, plants must often rely on other mechanisms to enable pollen transfer.

Some plants like grasses use wind to blow pollen onto the flower’s stigma, which captures pollen and starts the process of transmitting sperm in the pollen toward the egg of an ovule. But wind pollination is not very precise. Pollen can be blown onto the stigmas of flowers of the wrong species, or into the faces of animals – as the millions of us who suffer from hay fever can testify.

Enter the birds and the bees as important collaborators. Better than walk, these guys can fly very quickly between flowers to deliver pollen.

But, as Charles Darwin postulated, birds and bees will not evolve to do this unless there is a fitness benefit to them. A nutritional reward like nectar or the nitrogen-rich pollen itself is the reward that encourages birds and bees to fly between flowers searching for more rewards, and incidentally transferring the pollen while doing so.