The daily dance of flowers tracking the sun is more fascinating than most of us realise

Julien Christ/Unsplash

Gregory Moore, The University of MelbourneWhen I was a child, I was intrigued by the Queensland box (Lophostemon confertus) growing in our backyard. I noticed its leaves hung vertical after lunch in summer, and were more or less horizontal by the next morning.

This an example of heliotropism, which literally means moving in relation to the sun. We can see it most clearly as spring arrives and various species burst into flower — you might even get the feeling that some flowers are watching you as they move.

Many of us probably first got to know of heliotropism at home, kindergarten or primary school by watching the enormous yellow and black flowering heads of aptly name sunflowers, which moved as they grew.

These flowers track the course of the sun spectacularly on warm and sunny, spring or summer days. Sometimes they move through an arc of almost 180⁰ from morning to evening.

So with the return of sunny days and flowers in full bloom this season, let’s look at why this phenomenon is so interesting.

The mechanics of tracking the sun

A number flowering species display heliotropism, including alpine buttercups, arctic poppies, alfalfa, soybean and many of the daisy-type species. So why do they do it?

This is Heliotropium arborescens, named for its heliotropism. They were very popular in gardens a century or more ago, but have fallen from favour as they can be poisonous and weedy.
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Flowers are really in the advertising game and will do anything they can to attract a suitable pollinator, as effectively and as efficiently as they can. There are several possible reasons why tracking the sun might have evolved to achieve more successful pollination.

By tracking the sun, flowers absorb more solar radiation and so remain warmer. The warmer temperature suits or even rewards insect pollinators that are more active when they have a higher body temperature.

Optimum flower warmth may also boost pollen development and germination, leading to a higher fertilisation rate and more seeds.

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So, the flowers are clearly moving. But how?

For many heliotropic flowering species, there’s a special layer of cells called the pulvinus just under the flower heads. These cells pump water across their cell membranes in a controlled way, so that cells can be fully pumped up like a balloon or become empty and flaccid. Changes in these cells allow the flower head to move.

Fly traps have somewhat similar mechanics to heliotropism.
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When potassium from neighbouring plant cells is moved into the cells of the pulvinus, water follows and the cells inflate. When they move potassium out of the cells, they become flaccid.

These potassium pumps are involved in many other aspects of plant movement, too. This includes the opening and closing of stomata (tiny regulated leaf apertures), the rapid movement of mimosa leaves, or the closing of a fly trap.

But sunflowers dance differently

In 2016, scientists discovered that the pin-up example of heliotropism — the sunflower — had a different way of moving.

They found sunflower movement is due to significantly different growth rates on opposite sides of the flowering stem.

Sunflowers move differently to other heliotropic flowers.
Aaron Burden/Unsplash

On the east-facing side, the cells grow and elongate quickly during the day, which slowly pushes the flower to face west as the daylight hours go by — following the sun. At night the west-side cells grow and elongate more rapidly, which pushes the flower back toward the east over night.

Everything is then set for the whole process to begin again at dawn next day, which is repeated daily until the flower stops growing and movement ceases.

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While many people are aware of heliotropism in flowers, heliotropic movement of leaves is less commonly noticed or known. Plants with heliotropic flowers don’t necessarily have heliotropic leaves, and vice versa.

Heliotropism evolves in response to highly specific environmental conditions, and factors affecting flowers can be different from those impacting leaves.

The leaves of Queensland box, Lophostemon confertus, which track the sun.
Krzysztof Ziarnek, Kenraiz/Wikimedia Commons, CC BY-SA

For example, flowers are all about pollination and seed production. For leaves, it’s for maximising photosynthesis, avoiding over-heating on a hot day or even reducing water loss in harsh and arid conditions.

Some species, such as the Queensland box, arrange their leaves so they’re somewhat horizontal in the morning, capturing the full value of the available sunlight. But there are also instances where leaves align vertically to the sun in the middle of the day to minimise the risks of heat damage.

Plants are dynamic

It’s easy to think of plants as static organisms. But of course, they are forever changing, responding to their environments and growing. They are dynamic in their own way, and we tend to assume that when they do change, it will be at a very slow and steady pace.

Heliotropism shows us this is not necessarily the case. Plants changing daily can be a little unsettling in that we sense a change but may not be aware of what is causing our unease.

As for me, I still keep a watchful eye on those Queensland boxes!

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Gregory Moore, Doctor of Botany, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Flies like yellow, bees like blue: how flower colours cater to the taste of pollinating insects

Hoverfly (Eristalis tenax) feeding on marigold.
Fir0002/Flagstaffotos, CC BY-NC

Jair Garcia, RMIT University; Adrian Dyer, RMIT University, and Mani Shrestha, Bayreuth UniversityWe all know the birds and the bees are important for pollination, and we often notice them in gardens and parks. But what about flies?

Flies are the second most common type of pollinator, so perhaps we should all be taught about the bees, the flies and then the birds. While we know animals may see colour differently, little was known about how fly pollination shapes the types of flowers we can find in nature.

In our new study we address this gap in our knowledge by evaluating how important fly pollinators sense and use colour, and how fly pollinated flowers have evolved colour signals.

Specialed flower visiting flies: a hoverfly (Eristalis tenax) (left panel), and a bee-fly (Poecilanthrax apache) (right panel)
Michael Becker, Pdeley

The way we see influences what we choose

We know that different humans often have preferences for certain colours, and in a similar way bees prefer blue hues.

Our colleague Lea Hannah has observed that hoverflies (Eristalis tenax) are much better at distinguishing between different shades of yellow than between different blues. Other research has also reported hoverflies have innate responses to yellow colours.

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The mystery of the blue flower: nature’s rare colour owes its existence to bee vision

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Many flowering plants depend on attracting pollinators to reproduce, so the appearance of their flowers has evolved to cater to the preferences of the pollinators. We wanted to find out what this might mean for how different insects like bees or flies shape flower colours in a complex natural environment where both types of insect are present.

The Australian case study

Australia is a natural laboratory for understanding flower evolution due to its geological isolation. On the mainland Australian continent, flowers have predominately evolved colours to suit animal pollination.

Around Australia there are plant communities with different pollinators. For example, Macquarie Island has no bees, and flies are the only animal pollinator.

We assembled data from different locations, including a native habitat in mainland Australia where both bees and flies forage, to model how different insects influence flower colour signal evolution.

Measuring flower colours

Since we know different animals sense colour in different ways, we recorded the spectrum of different wavelengths of light reflected from the flowers with a spectrometer. We subsequently modelled these spectral signatures of plant flowers considering animal perception, allowing us to objectively quantify how signals have evolved. These analyses included mapping the evolutionary ancestry of the plants.

Generalisation or specialisation?

According to one school of thought, flower evolution is driven by competition between flowering plants. In this scenario, different species might have very different colours from one another, to increase their chances of being reliably identified and pollinated. This is a bit like how exclusive brands seek customers by having readily identifiable branding.

An alternative hypothesis to competition is facilitation. Plants may share preferred colour signals to attract a higher number of specific insects. This explanation is like how some competing businesses can do better by being physically close together to attract many customers.

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Our results demonstrate how flower colour signalling has dynamically evolved depending on the availability of insect pollinators, as happens in marketplaces.

In Victoria, flowers have converged to evolve colour signals preferred by their pollinators. The flowers of fly-pollinated orchids are typically yellowish-green, while closely related orchids pollinated by bees have more bluish and purple colours. The flowers appeared to share the preferred colours of their main pollinator, consistent with a facilitation hypothesis.

Typical flowers preferred by bees (Lobelia rhombifolia, left panel) and flies (Pterostylis melagramma, right panel) encountered in our study sites. Inserts show the spectral profile for each species as measured by a spectrometer.
Mani Shrestha

Our research showed flies can see differences between flowers of different species in response to the pollinator local “market”.

On Macquarie Island, where flies are the only pollinators, flower colours diverge from each other – but still stay within the range of the flies’ preferred colours. This is consistent with a competition strategy, where differences between plant species allow flies to more easily identify the colour of recently visited flowers.

When both fly and bee pollinators are present, flowers pollinated by flies appear to “filter out” bees to reduce the number of ineffective and opportunistic visitors. For example, in the Himalayas specialised plants require flies with long tongues to access floral rewards. This is similar to when a store wants to exclusively attract customers specifically interested in their product range.

Our findings on fly colour vision, along with novel precision agriculture techniques, can help using flies as alternative pollinators of crops. It also allows us to understand that if we want to see a full range of pollinating insects including beautiful hoverflies in our parks and gardens, we need to plant a range of flower types and colours.

Jair Garcia, Research fellow, RMIT University; Adrian Dyer, Associate Professor, RMIT University, and Mani Shrestha, Postdoc & International Fellow, Disturbance Ecology, Bayreuth University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Scientists are more likely to study bold and beautiful blooms, but ugly flowers matter too

Myricaria germanica is a rare and endangered species hit hard by climate change, but little research is undertaken to help save it.
Martino Adamo, Author provided

Kingsley Dixon, Curtin UniversityWe all love gardens with beautiful flowers and leafy plants, choosing colourful species to plant in and around our homes. Plant scientists, however, may have fallen for the same trick in what they choose to research.

Our research, published today in Nature Plants, found there’s a clear bias among scientists toward visually striking plants. This means they’re more likely chosen for scientific study and conservation efforts, regardless of their ecological or evolutionary significance.

To our surprise, colour played a major role skewing researcher bias. White, red and pink flowers were more likely to feature in research literature than those with dull, or green and brown flowers. Blue plants — the rarest colour in nature — received most research attention.

But does this bias matter? Plants worldwide are facing mass extinction due to environmental threats such as climate change. Now, more than ever, the human-induced tide of extinction means scientists need to be more fair-handed in ensuring all species have a fighting chance at survival.

Hidden plants in carpets of wildflowers

I was part of an international team that sifted through 280 research papers from 1975 to 2020, and analysed 113 plant species found in the southwestern Alps in Europe.

The Alps is a global biodiversity hotspot and the subject of almost 200 years of intensive plant science. But climate change is now creating hotter conditions, threatening many of its rarest species.

Edelweiss is a charismatic plant of the Alps that heralds spring.
Shutterstock

Carpeted in snow for much of the year, the brief yet explosive flowering of Europe’s alpine flora following the thaw is a joy to behold. Who was not bewitched when Julie Andrews danced in an alpine meadow in its full spring wildflower livery in The Sound of Music? Or when she sung “edelweiss”, one of the charismatic plants of the Alps that heralds spring?

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Hidden in these carpets of bright blue gentians and Delphiniums, vibrant daisies and orchids, are tiny or dull plants. This includes small sedges (Carex species), lady’s mantle (Alchemilla species) or the snake lily (Fritillaria) with its sanguine drooping flowers on thin stems.

Many of these “uncharismatic plants” are also rare or important ecological species, yet garner little attention from scientists and the public.

Bellflowers (Campanula) are conspicuous and prominent in the Alps.
Martino Adamo, Author provided

The plants scientists prefer

The study asked if scientists were impartial to good-looking plants. We tested whether there was a relationship between research focus on plant species and characteristics, such as the colour, shape and prominence of species.

Along with a bias towards colourful flowers, we found accessible and conspicuous flowers were among those most studied (outside of plants required for human food or medicine).

Bold and beautiful flowers in alpine meadows win scientific attention.
Martino Adamo, Author provided

This includes tall, prominent Delphinium and larkspurs, both well-known garden delights with well-displayed, vibrant flowers that often verge on fluorescent. Stem height also contributed to how readily a plant was researched, as it determines a plant’s ability to stand out among others. This includes tall bellflowers (Campanula species) and orchids.

But interestingly, a plant’s rarity didn’t significantly influence research attention. Charismatic orchids, for example, figured prominently despite rarer, less obvious species growing nearby, such as tiny sedges (Cypreaceae) and grass species.

The consequences of plant favouritism

This bias may steer conservation efforts away from plants that, while less visually pleasing, are more important to the health of the overall ecosystem or in need of urgent conservation.

In this time of urgent conservation, controlling our bias in plant science is critical. While the world list of threatened species (the IUCN RED List) should be the basis for guiding global plant conservation, the practice is often far from science based.

Mat rushes are home for rare native sun moths.
Shutterstock

We often don’t know how important a species is until it’s thoroughly researched, and losing an unnoticed species could mean the loss of a keystone plant.

In Australia, for example, milkweeds (Asclepiadaceae) are an important food source for butterflies and caterpillars, while grassy mat rushes (dull-flowered Lomandra species) are now known to be the home for rare native sun moths. From habitats to food, these plants provide foundational ecological services, yet many milkweed and mat rush species are rare, and largely neglected in conservation research.

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Likewise, we can count on one hand the number of scientists who work on creepy fungal-like organisms called “slime molds”, compared to the platoons of scientists who work on the most glamorous of plants: the orchids.

Yet, slime molds, with their extraordinary ability to live without cell walls and to float their nuclei in a pulsating jelly of cytoplasm, could hold keys to all sorts of remarkable scientific discoveries.

Slime molds could hold the key to many scientific discoveries, but the organisms are understudied.
Shutterstock

We need to love our boring plants

Our study shows the need to take aesthetic biases more explicitly into consideration in science and in the choice of species studied, for the best conservation and ecological outcomes.

While our study didn’t venture into Australia, the principle holds true: we should be more vigilant in all parts of the conservation process, from the science to listing species for protection under the law. (Attractiveness bias may affect public interest here, too.)

So next time you go for a bushwalk, think about the plants you may have trodden on because they weren’t worth a second glance. They may be important to native insects, improve soil health or critical for a healthy bushland.

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Kingsley Dixon, John Curtin Distinguished Professor, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The mystery of the blue flower: nature’s rare colour owes its existence to bee vision

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Adrian Dyer, RMIT University

At a dinner party, or in the schoolyard, the question of favourite colour frequently results in an answer of “blue”. Why is it that humans are so fond of blue? And why does it seem to be so rare in the world of plants and animals?

We studied these questions and concluded blue pigment is rare at least in part because it’s often difficult for plants to produce. They may only have evolved to do so when it brings them a real benefit: specifically, attracting bees or other pollinating insects.

We also discovered that the scarcity of blue flowers is partly due to the limits of our own eyes. From a bee’s perspective, attractive bluish flowers are much more common.

A history of fascination

The ancient mask of the pharaoh Tutankhamun is decorated with lapis lazuli and turquoise.
Roland Unger / Wikimedia, CC BY-SA

The ancient Egyptians were fascinated with blue flowers such as the blue lotus, and went to great trouble to decorate objects in blue. They used an entrancing synthetic pigment (now known as Egyptian blue) to colour vases and jewellery, and semi-precious blue gemstones such as lapis lazuli and turquoise to decorate important artefacts including the Mask of Tutankhamun.

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Blue dye for fabric is now common, but its roots lie in ancient Peru, where an indigoid dye was used to colour cotton fabric about 6000 years ago. Indigo blue dyes reached Europe from India in the 16th century, and the dyes and the plants that produced them became important commodities. Their influence on human fashion and culture are still felt today, perhaps most obviously in blue jeans and shirts.

Renaissance painters in Europe used ground lapis lazuli to produce dazzling works that captivated audiences.

The Virgin in Prayer by the Italian painter Sassoferrato, circa 1650, highlights the vivid blue colour made with ground lapis lazuli.

Today many blues are created with modern synthetic pigments or optical effects. The famous blue/gold dress photograph that went viral in 2015 not only shows that blue can still fascinate — it also highlights that colour is just as much a product of our perception as it is of certain wavelengths of light.

Why do humans like blue so much?

Colour preferences in humans are often influenced by important environmental factors in our lives. An ecological explanation for humans’ common preference for blue is that it is the colour of clear sky and bodies of clean water, which are signs of good conditions. Besides the sky and water, blue is relatively rare in nature.

What about blue flowers?

We used a new online plant database to survey the the relative frequencies of blue flowers compared to other colours.

Among flowers which are pollinated without the intervention of bees or other insects (known as abiotic pollination), none were blue.

But when we looked at flowers that need to attract bees and other insects to move their pollen around, we started to see some blue.

This shows blue flowers evolved for enabling efficient pollination. Even then, blue flowers remain relatively rare, which suggests it is difficult for plants to produce such colours and may be a valuable marker of plant-pollinator fitness in an environment.

Global flower colour frequency for human visual perception (A) shows when considering animal pollinated species less than 10% are blue (B), and for wind pollinated flowers almost none are observed to be blue (C).
Dyer et al., Author provided

We perceive colour due to how our eyes and brain work. Our visual system typically has three types of cone photoreceptors that each capture light of different wavelengths (red, green and blue) from the visible spectrum. Our brains then compare information from these receptors to create a perception of colour.

For the flowers pollinated by insects, especially bees, it is interesting to consider that they have different colour vision to humans.

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Inside the colourful world of animal vision

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Bees have photoreceptors that are sensitive to ultraviolet, blue and green wavelengths, and they also show a preference for “bluish” colours. The reason why bees have a preference for bluish flowers remains an open field of research.

Various blue flowers from our study.

Why understanding blue flowers is important

About one-third of our food depends on insect pollination. However, world populations of bees and other insects are in decline, potentially due to climate change, habitat fragmentation, agricultural practices and other human-caused factors.

The capacity of flowering plants to produce blue colours is linked to land use intensity including human-induced factors like artificial fertilisation, grazing, and mowing that reduce the frequency of blue flowers. In contrast, more stressful environments appear to have relatively more blue floral colours to provide resilience.

For example, despite the apparent rarity of blue flower colours in nature, we observed that in harsh conditions such as in the mountains of the Himalaya, blue flowers were more common than expected. This shows that in tough environments plants may have to invest a lot to attract the few available and essential bee pollinators. Blue flowers thus appear to exist to best advertise to bee pollinators when competition for pollination services is high.

Knowing more about blue flowers helps protect bees

Urban environments are also important habitats for pollinating insects including bees. Having bee friendly gardens with flowers, including blue flowers that both we and bees really appreciate, is a convenient, pleasurable and potentially important contribution to enabling a sustainable future. Basically, plant and maintain a good variety of flowers, and the pollinating insects will come.

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Adrian Dyer, Associate Professor, RMIT University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Tiny treetop flowers foster incredible beetle biodiversity

Hundreds of beetle species seem to be specialists that feed only from small white flowers on trees.
Susan Kirmse, CC BY-ND

Caroline S. Chaboo, University of Nebraska-Lincoln

The Research Brief is a short take on interesting academic work.

The big idea

Biologists have long known that rainforest treetops support a huge number of beetle species, but why these canopies are so rich in beetle diversity has remained a mystery. New research by my colleague Susan Kirmse and me shows that flowering trees play a critical role in maintaining this diversity, and that beetles may be among the most diverse pollinators in the animal kingdom.

We carried out a one-year study in a remote part of the Amazon rainforest in Venezuela. We used a specially built crane to collect a total of 6,698 adult beetles representing 859 species. These were gathered from 45 individual trees of 23 different tree species.

We were surprised to discover that the majority of these beetles – 647, or 75.3% of species found – were living on flowering trees. In fact, 527 beetle species in 41 families were associated exclusively with flowers. Interestingly, the majority of these species – almost 60% – were exclusively found on trees that produce lots of small white flowers.

Overall, this discovery shows that flowering trees are likely among the most important drivers for maintaining the high diversity of beetles in rainforests. But this relationship goes both ways. Our study also suggests that beetles may be among the most underappreciated pollinators in tropical forests.

Using a specialized crane, the team was able to collect beetles from the very top of the forest canopy.
Susan Kirmse, CC BY-ND

Why it matters

Tropical rainforests are the very heart of Earth’s biodiversity. They harbor about 65% to 75% of all terrestrial species, including the most tree species and the most insects.

After finding such a tight relationship between beetles and flowering trees, we wondered: How many beetle species could be involved in pollination in the Amazon? Our study found an average of 26.35 unique beetle species for every species of tree. With an estimated 16,000 Amazonian tree species, this suggests that there might be more species of flower-visiting beetles than any other insects on Earth, potentially surpassing by far the 20,000 species of bees and the 19,000 species of butterflies.

Our study shows that flowering tree species play an important role as diversity hotspots in tropical rainforest canopies. For policymakers and biologists hoping to preserve or restore rainforests, promoting the cultivation of trees and other plants – especially those with lots of small white flowers that beetles love – could help to maintain species-rich communities. Flowers are a very important resource, providing food and shelter for thousands of insects in addition to beetles. Thus, preserving plant diversity or selecting many different indigenous tree species for reforestation can enhance the diversity of insects.

Beetles like the Griburius auricapillus are just some of the hundreds of species that can be found in treetops.
Susan Kirmse, CC BY-ND

What still isn’t known

Our research was the first to describe this tight relationship between beetles and rainforest trees, especially with trees that produce thousands of small, simple flowers. But how this association came to be is still unclear.

Many of the beetle species were found only on trees with this particular type of flower. The trees get an obvious benefit: pollination. But what specifically these trees offer to the beetles requires further study. The simpler flowers are easier for beetles to access, but is the appeal food, like petals, pollen or nectar? Or maybe a home to find mates or lay eggs for the young to grow?

[You’re smart and curious about the world. So are The Conversation’s authors and editors. You can get our highlights each weekend.]

What’s next

To fight the worldwide rapid declines in insect diversity, researchers and conservationists must understand the ecological connections between insects and their food plants. Long-term studies, particularly in research plots like the one we used in Venezuela, allow researchers to collect layers of information that help unravel the complexity of diversity.

Yet such sites rely on political interest and stability. Political instability in Venezuela is preventing our fieldwork from continuing at the Venezuela plot.

While we can’t return to our study site in Venezuela, it is clear that researchers must work together to understand the mysteries of life on Earth. But biologists are racing the clock as large rainforests are destroyed forever.

Caroline S. Chaboo, Adjunct Professor in Insect Systematics, University of Nebraska-Lincoln

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Flowering Time?

Waterplants Blooming

Rainforests: More Flowers Brought on by Climate Change

The link below is to an article that reports on a change to rainforests as a consequence of climate change – more flowers.

For more visit:
http://news.mongabay.com/2013/0709-climate-rainforest-shifts.html