STEP 3: COEVOLUTION; EVOLVING TOGETHER

Nature favors individuals that are best adapted to their environment. If an individual’s adaptations increase their ability to obtain resources, they are more likely to survive long enough to reproduce, thereby passing on beneficial traits. Over generations, these traits build up to produce new species specially adapted to the biotic and abiotic conditions of their environment (see Lesson 1). This is why native plants are always the best plants for pollinator gardens.

WHAT IS COEVOLUTION? 

Coevolution is when two or more species that interact with each other on a regular basis evolve in response to each other’s adaptations. This is how plants and their pollinators have evolved. Let’s take a look at some examples of plant-pollinator coevolution.

PLANT ADAPTATIONS

Plants develop new adaptations over time through cross-pollination. The adaptation will either increase their ability to attract pollinators and/or control which ones can access the nectar inside, preserving the valuable pollen and nectar for their loyal pollinator partners.
 

Flower size can act as a control for which pollinator species can access the nectar/pollen. Think about how big a bumblebee is: it wouldn’t be able to land on small, thin-stemmed plants without damaging them. Size can also act as a signal to pollinators, to show them where the flowers are. Large, boldly colored flowers stand out from afar for passing pollinators, especially on a bold green background.

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The 13″ American locus flower stands out, signaling their pollinator species where to find them.
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Honey bee collecting pollen on forget-me-not. A bumblebee can be 3X the size of a honey bee.

Flower shapes come in a variety of designs to ensure they are successfully cross-pollinated. Not all pollinators have the right set of tools to access nectar and pollen from every flower species. By evolving complex flower heads, flowers can control which pollinators can gain access. For example: Long, tubular flowers hide nectar deep inside, so only pollinators with long tongues like hummingbirds and some butterfly, moth, and bee species can reach the nectar.

Fig trees are pollinated by the female fig wasp. When the fig flower is ready to be pollinated it emits a scent that attracts female fig wasps. The fig’s opening is so small that, as the wasp enters the flower, she loses her wings and parts of her antennae. She lays her eggs inside the flower and dies shortly thereafter. As her offspring emerge from the flower, they carry pollen from that flower to others and pollinate the next generation of fig trees.

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Because nature is constantly evolving, so is flower head design.
These are the commonly known shapes, but most flowers will be some sort of variation or combination of these shapes.
(See the “Plant Shapes and Pollinators” chart in Step 4: Research Pollinators in Your Area)
 
Flower color is a way for plants to signal their pollinator partners, by displaying distinct colors that stand out to their pollinators. Pollinators can’t see all the same colors as humans do, and don’t see them the same way as we do. Different pollinators also see different colors. Bees and wasps can’t see red, but they can see ultraviolet light. Butterflies and birds can see the color red, so red plants will primarily be pollinated by birds and butterflies.
 

FUN FACT
Bees and wasps see the color black as a threat because it mimics potential predators like bears and skunks. Their eyes cannot process the color red either, so it comes up as black to them too.

Ever been stung by one and thought you didn’t deserve it? It may have been because you were wearing black or red clothes.

Nectar guides are the plant’s way of showing pollinators exactly where their nectar reward can be found. They can be both visible and invisible to the human eye. Because some flowers have ultra violet nectar guides, this would indicate some of their pollinator partners are bees, wasps, or butterflies, because they have the ability to see U.V. light. Some plant species lose their nectar guides when the nectar is gone, stopping the pollinator from wasting time visiting an empty flower. How considerate.
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Visible nectar guides.
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UV nectar guides for bee, wasps, and butterflies.
Try this with bee-pollinated plants: Using a UV light, turn off the other lights in your room and shine the UV light above the flower. 
You should see a change in color at the flowers center where the nectar is located.
Flower fragrance/scent is another way to signal pollinators to their location. These flowers won’t be as colourful. They will usually be white, brown with hints of red or purple, or sometimes green. Scent can be detected up to 1 km away. Flowers that bloom at night will also emit strong scents because it’s easier for bats and moths to locate flowers by scent than by sight alone. Not all pollinators have a strong sense of smell either, so they would only signal certain pollinator species, increasing their chances of successful cross-pollination.
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ACTIVITY

Now that you know that bees see the world differently than we do,
this coloring exercise might still surprise you!

POLLINATOR ADAPTATIONS

Pollinator species adapt to their pollinator plants through physical evolutionary changes over time, or more immediate behavioural changes, to maximize the pollinator’s ability to collect nectar and/or pollen, while achieving successful cross-pollination of their partner plant species.

Physical Adaptations

Proboscis length has evolved with different species. The proboscis in insect pollinators is a sucking mouth appendage that allows the pollinator insect to take up nectar. The length of their proboscis varies between species, depending on the flowers they feed on. Butterflies and moths have a long thin proboscis that allows them to access nectar from long, tubular, funnel, trumpet, spurred, and salverform-shaped flowers—while bees, flies, and beetles generally have a shorter proboscis, so they feed on more open, saucer, bell, cup, bowl and strap-shaped flowers. Bats and birds use their tongues to consume nectar, which also varies in length between species.
Pollinator hairs
Photos courtesy of © Stephanie Young

Body hairs or setae, found on the bodies of many pollinator species— butterflies, flies, moths and bees—are like “velcro.” As the pollinator reaches into the flower to find the nectar, pollen attaches to the hairs until it’s knocked off when entering another flower.

Bees have developed specialized hairs that form baskets on their hind legs to carry pollen back to the nest—colonial bees collect pollen to make “bee bread,” a staple food for their workers and young.

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Photo courtesy of © Stephanie Young
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Static electricity is one of the main reasons why bees are such great pollinators. The vibrations from their wings create a positive static electrical charge, which is stored in the hairs on their body, acting as a magnet for pollen. Flowers generate a small negative charge as they move in the wind; when pollinators visit the flower, its static energy is released. Because bee hairs are sensitive to static charges, they can tell if a flower has recently been visited and move on to the next flower without wasting time on empty ones. 

Behavioral Adaptations

Behavioral adaptations are more instant changes a species can make in order to survive its environment. For example: Monarch butterflies migrate south during winter in search of warmer climates and suitable food sources because they don’t hibernate through winter months.

Foraging is the collection of food resources. Some pollinators methodically forage pollen and nectar. Honeybees forage in a specific way, close to their colony, so they can easily transport the nectar and pollen they collect, without wasting too much time and energy traveling between places. Also, they collect nectar and pollen from one species of flower before moving onto a different species. This type of collection increases the chances of successful cross-pollination, because the pollen will only be transferred to a flower of the same species. 

Buzz pollination is another way bees have repurposed their abilities to their advantage. They vibrate their wings while they are inside the flower, dislodging large amounts of pollen that are attracted to their static hairs. This also dislodges pollen already on them, increasing pollination chances and the amount of pollen they collect.

Hovering is a flight adaptation in hummingbirds and hummingbird hawk moths that allows them to move between flowers faster than if they had to perch at each flower, like other nectar feeding birds have to do. The ability to hover gives them access to flowers not available to other pollinators.

SUMMARY

Plants evolve to attract pollinators and/or restrict nectar access to certain species, while pollinators adapt physically or behaviourally to increase the efficiency of their resource intake. Together these adaptations increase cross-pollination success, and resource provision intake. Everyone’s a winner! 

Now it’s your turn…

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ACTIVITY

MATCH PLANTS WITH POLLINATORS

AND GO DEEPER
The activity includes the following charts for next-level thinking to facilitate completion of the activity:
 Pollinator Syndrome Chart
Flower Chart

Copyright © New England Primate Conservancy 2021. You may freely use, copy and share these Learning Activities for educational purposes. 
​For questions or comments, e-mail us at [email protected]