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Flowers of the Impatiens genus and their specialization in pollination techniques

Posted on 02-11-2017 by Toine Baken

The species of the genus Impatiens have evolved different, asymmetric shapes, driven by competition between one another in pollination by animals. 

In a study in the Botanical Journal of the Linnean Society, researchers (including 4  from Naturalis) have presented their results on specialization in pollination techniques in flowers of the genus Impatiens. For two months in 2014, they have studied 7 co-occurring species of the genus Impatiens (see video) in the Chiang Dao Wildlife Sanctuary in Chiang Mai, Thailand.

Around the world, there are more than 1000 species of this plant. Their flowers vary extensively in colour, shape and size. Often, variation in flower morphology among species that are closely related is prescribed to differences in pollination techniques.  The pollination ecology of flowers in this genus, however, had not yet been well studied in comparative context. With this goal, researchers closely monitored the flowers and checked whether they relied on pollinators (animals) for reproduction. They identified which animals were attracted to each flower and which animals acted as active pollinators for each flower. They also studied and compared the shapes of the flowers and their nectar characteristics and compared these traits to which animals and which parts of animals acted as pollinators. 

Impatiens

The studied flowers of the genus Impatiens.

They found that most flowers were visited by multiple animal species, however, for each flower only a few of these animals were effective pollinators. For each flower, a specific subset of animals was most effective for pollination and this subset differs per species. Whether an animal is an effective pollinator for a flower seems to be influenced by the flower shape and whether they produce nectar. For example: an autogamous flower is small and spurless and does not produce nectar, since they do not need pollinators for reproduction. Flowers that use bees as effective pollinator had short spurs and large floral chambers with a wide entrance. This way, the flower species of Impatiens have all adapted a specific morphology to avoid reproduction competition among one another.

Some pollinators, however, are shared by multiple flowers, such as bees. The results also showed that flowers that share an animal as pollinator have also adapted a certain floral shape that pollinates specific parts of that animal. Each of these flowers pollinate a different part of the animal through their specific and often asymmetric shape and as such they avoid competition among one another, even though the same pollinator is used. This is a good example of how competition in pollination between closely related species drives evolution in floral morphology and asymmetry.

Curious about what these flowers look like? Check the video below, made by the lead author and Naturalis researcher Saroj Ruchisansakun, or the original paper

Flowers of the Impatiens genus: shapes and pollination


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