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The Busy Business Of How Bees Interact With Flowers And Their Pollen

November 20, 2014

Photo Credit: http://mrg.bz/G2SfcE

The transferring of male and female sex cells is what makes the world go round, yet unlike animals most plants have an inability to control this process directly. Approximately 75% of the flowering plants on the planet rely on animals to move their pollen from flower to flower and few animals are better at this task than the bee (Mitchell et al. 2009). Honeybees and bumblebees are foraging pollinators who can travel many miles, 1 mile for bumblebees and 6 miles for honeybees, in search of flowers to obtain pollen and make that delicious substance we all know and love, honey. But what happens before the bee makes it back to the hive? What kind of say does the plant have in all this honey talk? It turns out the flowers actions are louder than the bee’s buzz.

To Bee A Generalist Or Not To Bee?

Looking at a collection of studies researchers found it all came down to the cost of the interaction, who benefits, how much, and if it’s worth the meeting. Plant species with a wide array of pollinators show little specialization, they are generalists whose pollen is adaptable and can be spread with relative ease. Other plant species lean more towards the specialization side, a lavender species with deep corolla tubes or varying sizes of styles. These specialist plants have adapted certain traits making it easier for the most efficient pollinators to do their job and the benefits help both parties. The plant rewards the pollinator with its organically expensive pollen whereas the plant gets to have its genes dispersed to different areas without having to move a root.

 

Honeybee with lavender. Photo Credit: http://mrg.bz/DpGNnX

What About Bee Tongues?

In a study looking at the attractiveness of garden plants the researchers wanted to find out which factors were important to specific pollinators (Garbuzov and Ratnieks 2014). They used native and non-native plants along with exotic species to see if there was a difference in visitation frequency. It turned out it didn’t matter where the plants came from, one of the things that did was the corolla tube length. The corolla tube is the tunnel traveling down the middle part of the flower face, the place where the stigma (female pollen receiver) and anthers (male pollen producer) are jetting out. The reason the tube length mattered was due to the length of bee tongues, bees being the most common visitor to the garden plants, accounting for 84% of the overall visitation. Of these bees one-third were honeybees who happen to have an average tongue length of 6.6 mm whereas the rest of the bees were bumblebees, average tongue length of 7.8 mm. The average corolla tube length was 7.2 mm, meaning the honeybees were selected against since their tongues couldn’t reach far enough into the tube to efficiently retrieve the pollen, the bumblebees could and these species of flowers had higher levels of bumblebee visits. This plays a role in the evolution of both the bees and the plant. Since the bumblebees have the ability to reach deeper tubes they will be the only ones to pollinate the deep corolla tubed plants. This will show a selection preference for deeper tubed plants and longer tongued bumblebees. Eventually there will be the optimum tongue length and corolla tube depth which will be seen more often, effectively preventing the honeybees from pollinating a specific group of flowers, those with deeper corolla tubes.

Other species with longer corolla tubes weren’t so picky, they had long tubes yet the openings were wider so the shorter tongued honeybees could crawl into the tube and reach the pollen. The study leaned towards pollinators, especially bees, being quite adaptive in their choice of flowers to pollinate, not really worrying about much else besides pollen availability and the ease with which they could obtain it (Chittka and Raine 2006). Yet, when discussing the corolla tube there is a wide range of anatomy, both from the plants body as well as the pollinators, useful in understanding the act of pollination.

 

Honeybee surrounded by anthers (yellow tips). Photo Credit: http://mrg.bz/U72Eq0

So What’s Wrong With My Style?

Honeybees are the main pollinators of flowering plants around the world mostly due to the construction of their bodies and the way they live. They have hairy bodies which are great to trap the pollen grains, the male sex cells produced from the anther, which remain attached from flower to flower with some coming in contact with the stigma. The stigma is situated on top of the style, a tube, which runs down to the ovary of the flower. It turns out how long the style stretches determines a lot about the plant, whether it will be a pollen recipient and how much pollen each plant receives. When looking at plants in the Solanaceae family, (Solanum carolinense) a study found flowers containing a long style were primarily pollen recipients whereas flowers with short styles acted as pollen donors (Quesada-Aguilar et al 2008). If a flower had long styles the pollen was more likely to come in contact with the bee body more often and remained attached better than short styles. Natural studies of flowers determined a style length of 9 mm was the most likely to fruit whereas styles of greater than 15 mm received very little pollen while 9-13 mm received the most. This shows an interaction between the pollinators and the plants themselves. This 9-13 mm range is the optimum pollen receiving zone due to the types of pollinators and how they have influenced the S. carolinense over generations. Flowers within this style range produce more offspring when compared with those with less than 9 mm and greater than 13 mm styles. Eventually the S. carolinense plants living in a given community will be mostly those with the 9-13 mm style range, due to the interaction of the pollinators. This will be beneficial to the S. carolinense by allowing more of their population to fruit which will in turn be beneficial to the bee population for pollination.

 

Bee with S. carolinense. Photo Credit: Lachlan Cranswick

The Big Picture

The process of pollination is an elegant venture, simple when viewed from a human’s point of view but quite complex when viewed through the many hairy lenses of a bee. Ranging from the generalist plants whose method is whatever pollinator will do the job to the specialist plants who have designed a unique lock and key method for efficiently obtaining their precious pollen, the interaction is amazing. The two are intricately dependent on one another for survival and the interaction between the two will drive each others evolution. Without the plants there will be no bees and without the two of them our world will be a very different place. Next time you use honey in a beverage be sure to raise your glass to complexity of nature and simplicity of the busy bees and the plants they work alongside!

 

 

 

References

1. Chittka L, Raine NE (2006) Recognition of flowers by pollinators. Curr Opin Plant Biol 9:428-435

2. Garbuzov M, Ratnieks FLW (2014) Quantifying variation among garden plants in attractiveness to bees and other flower-visiting insects. Funct Ecol 28:364-374

3. Mitchell RJ, Irwin RE, Flanagan RJ, Karron JD (2009) Ecology and evolution of plant-pollinator interactions. Ann Bot-London 103:1355-1363

4. Quesada-Aguilar A, Kalisz S, Ashman TL (2008) Flower morphology and pollinator dynamics in Solanum carolinense (Solanaceae): Implications for the evolution of andromonoecy. Am J Bot 95(8): 974-984

Photo Credit:

5. Cranswick L (2002) Bee and S. Carolinense [Internet]. New York; [cited 2014 Nov 20]. Available from http://lachlan.bluehaze.com.au/usa2002/june2002/28jun2002c/mvc-010f.jpg

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One Comment leave one →
  1. November 22, 2014 8:20 am

    Excellent post! Always love to learn about the science behind what we see everyday.

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