UV coloration in flowers

Last updated April 09, 2024

Dandelion under both UV light coloration (left) and visible light coloration (right). Dandelion-SAD-2022.jpg — Dandelion under both UV light coloration (left) and visible light coloration (right).

UV coloration is a natural phenomenon that leads to unique interactions between organisms that have evolved the ability to perceive these wavelengths of light. It serves as one method to attract pollinators to the flower along with scent, shape, and nectar quality.^[1] Flowers are known for their range of visible colors that humans can see with their eyes and observe an array of different shades and patterns.^[2] The naked eye cannot see the ultraviolet coloration many flowers employ to bring attention to themselves.^[3] By either reflecting or absorbing UV light waves, flowers are able to communicate with pollinators.^[4] This allows plants that may require an animal pollinator to stand out from other flowers or distinguish where their flowers are in a muddied background of other plant parts.^[5] For the plant, it is important to share and receive pollen so they can reproduce, maintain their ecological role, and guide the evolutionary history of the population.

Background

Ultraviolet light is a form of electromagnetic radiation that ranges in wavelengths from 10 nm to 400 nm.^[6] This wavelength is shorter than visible light but longer than X-rays.^[6] As it sits on the lower edge of visible light, is what gives its name. The most effective wavelength of UV light is approximately 250 nm.^[6] It was discovered in 1801 by German scientist Johann Wilhelm Ritter when he noticed that paper soaked with silver chloride darkened faster than regular paper when hit by sunlight.^[6] Then in 1878, UV light was first observed to have the ability to kill bacteria which led to understanding how UV can damage cells and mutate DNA in 1960.^[6] At that point they began to refer to it as “ionizing radiation” for the harmful impacts the shorter wavelengths exhibited.^[6] Also it can be used in microscopy as a tag known by Green Fluorescent Protein (GFP) to track development and movement of structures within the cell when shined under UV emitting lightbulbs.^[6] Ultraviolet light has positive effects such as vitamin-D production in skin tissue and negative effects of sunburn damage and inflammation in the same part of the body.^[6]

Function by plants and pollinators

Ultraviolet coloration is used by 25 to 35 percent of angiosperms.^[7] It was adapted by flowers to orient pollinators leading to an example of co-evolution.^[8] UV light allows them to broadcast a guide to where their pollen is located.^[4] Due to unique life characteristics and morphology of flowers, pollinators are more effective at taking the pollen and spreading it to other flowers of the same species.^[3] Flowers have specifically adapted to consistently target a particular pollinator as their hue or intensity of coloration is in the peak wavelength for their pollinator to see and be attracted to.^[5] A flower’s size, shape, color, scent, and pattern all play a role in signaling with the senses of pollinators.^[2] Plants that rely on animal pollinators are most likely to use the UV coloration strategy compared to other plants to increase the odds of them being pollinated.^[7] Some examples of animal pollinators are bees, butterflies, beetles, flies, birds, bats, and a few small mammals.^[2] This wide range of species seek out the nectar produced by the plants as food source or in the famous case of honey bees the key ingredient for making honey. This is an example of mutualism where the pollinators receive a resource in exchange for aiding plants in their pollination and reproduction.^[1]

UV patterns can vary among like species and unlike species.^[1] UV reflection is independent of flower symmetry, but larger size does increase the frequency of reflection.^[2] The visible color of the flower impacts the UV color.^[9] Yellow flowers having the greatest measure of reflectance.^[5] It is more typical to observe UV coloration in purple, red and yellow flowers while white and green ones are less likely.^[2] Generally flowers that are white or green tend to be wind pollinated; where being a bright color isn't necessary.^[2] A common phenotype of UV coloration is the “bulls-eye” pattern where a flower reflects UV light at the ends of the petals and absorbs UV light in the center.^[4] This acts as a guide for pollinators to locate and find pollen.^[4] Other flowers add the contrast between their reproductive parts (anthers and pistils) and their petals.^[7] Flowers use chemical and physical structures within petal tissue to create UV coloration.^[2] For example, flavonoids are responsible for absorption of UV. As plants move into new environments they will continue to manipulate and shift their UV profile.^[4]

Evolution

As plants have evolved and adapted their UV coloration, pollinators have also fine-tuned their individual adaptations to maximize their ability to target flowers for food.^[8] The dynamic relationship between the pollinators and the pollinated has led to novel mutations and in some cases novel species.^[1] Pollinators are drivers of speciation as they are the crux of survival for plants that rely on them for reproductive success.^[1] This example of directional selection leads to convergent evolution of flower size, structure, and coloring patterns.^[1] For example, if a bee favors a flowers with larger petals then those individual will be more successful at reproduction leading to more and more individuals within a population to have large flowers. Pollinators demonstrate local environmental adaptations in their visual sensory response systems to the amount of light.^[5] It is shown that red and white flowers pollinated by bees are of higher spectral purity as compared to bird-pollinated ones and are therefore easier to detect for bees.^[8] Bees have trichromatic vision with maxima of peak sensitivities in UV (344 nm), blue (436 nm) and green (544 nm).^[10] Also, bees have preferential treatment towards flowers that use small guides and combine both UV reflectance and absorption has been documented many times in many locations.^[5] The interactions are very precise and slight changes in the intensity or size of UV reflectance and/or absorbance affects pollinator behavior along with rate of visitors.^[7] Therefore, decreased UV coloration on the petals leads to few exchanges of pollen with pollinators causing a reduction in an individual's evolutionary fitness.^[4]

Other examples of UV being used

While angiosperms take advantage of ultraviolet patterns to be seen, primitive gymnosperms have pollen that reflects UV light.^[10] This brings up questions on the evolutionary origins of this phenomenon. It is believed that reflecting UV light is actually a protective measure plants utilize to prevent DNA damage from the UV in sunlight.^[10] This is understandable as UV wavelengths can mutate and even destroy organic structures like DNA and skin tissue which is why humans experience sunburn.^[6] The pollen grains reflect UV-beta to shield their chromosomes stored in the pollen from UV-alpha which is important for making sure of reproductive success.^[10] The technique of UV coloration has evolved in other species as well for various reasons. Similarly, carnivorous plants reflect and absorb UV to attract prey to it.^[10] They mimic the strategy used by traditional flowers for pollination to exploit pollinators to land in the trap so the carnivorous flower head can digest them as a source of key nutrients to grow and survive. Butterflies, a common insect pollinator, use UV coloration in their wing patterns to achieve an extra level of modelling their fitness to potential mates.^[3]

Related Research Articles

The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high frequency these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications.

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, than the absorbed radiation. A perceptible example of fluorescence occurs when the absorbed radiation is in the ultraviolet region of the electromagnetic spectrum, while the emitted light is in the visible region; this gives the fluorescent substance a distinct color that can only be seen when the substance has been exposed to UV light. Fluorescent materials cease to glow nearly immediately when the radiation source stops, unlike phosphorescent materials, which continue to emit light for some time after.

Ultraviolet (UV) light is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs; Cherenkov radiation; and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights.

The visible spectrum is the band of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light. The optical spectrum is sometimes considered to be the same as the visible spectrum, but some authors define the term more broadly, to include the ultraviolet and infrared parts of the electromagnetic spectrum as well, known collectively as optical radiation.

Ultraviolet (UV) spectroscopy or ultraviolet–visible (UV–VIS) spectrophotometry refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible regions of the electromagnetic spectrum. Being relatively inexpensive and easily implemented, this methodology is widely used in diverse applied and fundamental applications. The only requirement is that the sample absorb in the UV-Vis region, i.e. be a chromophore. Absorption spectroscopy is complementary to fluorescence spectroscopy. Parameters of interest, besides the wavelength of measurement, are absorbance (A) or transmittance (%T) or reflectance (%R), and its change with time.

A pollinator is an animal that moves pollen from the male anther of a flower to the female stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains.

Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the corolla. Petals are usually accompanied by another set of modified leaves called sepals, that collectively form the calyx and lie just beneath the corolla. The calyx and the corolla together make up the perianth, the non-reproductive portion of a flower. When the petals and sepals of a flower are difficult to distinguish, they are collectively called tepals. Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa. Conversely, genera such as Rosa and Phaseolus have well-distinguished sepals and petals. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in petaloid monocots, orders of monocots with brightly colored tepals. Since they include Liliales, an alternative name is lilioid monocots.

<span class="mw-page-title-main">Spectrophotometry</span> Branch of spectroscopy

Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spectrophotometers, that can measure the intensity of a light beam at different wavelengths. Although spectrophotometry is most commonly applied to ultraviolet, visible, and infrared radiation, modern spectrophotometers can interrogate wide swaths of the electromagnetic spectrum, including x-ray, ultraviolet, visible, infrared, and/or microwave wavelengths.

Pseudocopulation describes behaviors similar to copulation that serve a reproductive function for one or both participants but do not involve actual sexual union between the individuals. It is most generally applied to a pollinator attempting to copulate with a flower. Some flowers mimic a potential female mate visually, but the key stimuli are often chemical and tactile. This form of mimicry in plants is called Pouyannian mimicry.

Nectar guides are markings or patterns seen in flowers of some angiosperm species, that guide pollinators to their rewards. Rewards commonly take the form of nectar, pollen, or both, but various plants produce oil, resins, scents, or waxes. Such patterns also are known as "pollen guides" and "honey guides", though some authorities argue for the abandonment of such terms in favour of floral guides. Pollinator visitation can select for various floral traits, including nectar guides through a process called pollinator-mediated selection.

A flower, also known as a bloom or blossom, is the reproductive structure found in flowering plants. Flowers consist of a combination of vegetative organs – sepals that enclose and protect the developing flower, petals that attract pollinators, and reproductive organs that produce gametophytes, which in flowering plants produce gametes. The male gametophytes, which produce sperm, are enclosed within pollen grains produced in the anthers. The female gametophytes are contained within the ovules produced in the carpels.

Ornithophily or bird pollination is the pollination of flowering plants by birds. This sometimes coevolutionary association is derived from insect pollination (entomophily) and is particularly well developed in some parts of the world, especially in the tropics, Southern Africa, and on some island chains. The association involves several distinctive plant adaptations forming a "pollination syndrome". The plants typically have colourful, often red, flowers with long tubular structures holding ample nectar and orientations of the stamen and stigma that ensure contact with the pollinator. Birds involved in ornithophily tend to be specialist nectarivores with brushy tongues and long bills, that are either capable of hovering flight or light enough to perch on the flower structures.

Ultraviolet photography is a photographic process of recording images by using radiation from the ultraviolet (UV) spectrum only. Images taken with ultraviolet radiation serve a number of scientific, medical or artistic purposes. Images may reveal deterioration of art works or structures not apparent under light. Diagnostic medical images may be used to detect certain skin disorders or as evidence of injury. Some animals, particularly insects, use ultraviolet wavelengths for vision; ultraviolet photography can help investigate the markings of plants that attract insects, while invisible to the unaided human eye. Ultraviolet photography of archaeological sites may reveal artifacts or traffic patterns not otherwise visible.

In zoology, a palynivore /pəˈlɪnəvɔːɹ/, meaning "pollen eater" is an herbivorous animal which selectively eats the nutrient-rich pollen produced by angiosperms and gymnosperms. Most true palynivores are insects or mites. The category in its strictest application includes most bees, and a few kinds of wasps, as pollen is often the only solid food consumed by all life stages in these insects. However, the category can be extended to include more diverse species. For example, palynivorous mites and thrips typically feed on the liquid content of the pollen grains without actually consuming the exine, or the solid portion of the grain. Additionally, the list is expanded greatly if one takes into consideration species where either the larval or adult stage feeds on pollen, but not both. There are other wasps which are in this category, as well as many beetles, flies, butterflies, and moths. One such example of a bee species that only consumes pollen in its larval stage is the Apis mellifera carnica. There is a vast array of insects that will feed opportunistically on pollen, as will various birds, orb-weaving spiders and other nectarivores.

Biological pigments, also known simply as pigments or biochromes, are substances produced by living organisms that have a color resulting from selective color absorption. Biological pigments include plant pigments and flower pigments. Many biological structures, such as skin, eyes, feathers, fur and hair contain pigments such as melanin in specialized cells called chromatophores. In some species, pigments accrue over very long periods during an individual's lifespan.

<span class="mw-page-title-main">Pollination syndrome</span> Flower traits that attract pollinators

Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic or biotic, such as birds, bees, flies, and so forth through a process called pollinator-mediated selection. These traits include flower shape, size, colour, odour, reward type and amount, nectar composition, timing of flowering, etc. For example, tubular red flowers with copious nectar often attract birds; foul smelling flowers attract carrion flies or beetles, etc.

Flower constancy or pollinator constancy is the tendency of individual pollinators to exclusively visit certain flower species or morphs within a species, bypassing other available flower species that could potentially contain more nectar. This type of foraging behavior puts selective pressures on floral traits in a process called pollinator-mediated selection. Flower constancy is different from other types of insect specialization such as innate preferences for certain colors or flower types, or the tendency of pollinators to visit the most rewarding and abundant flowers.

Thomisus onustus is a crab spider belonging to the genus Thomisus. These spiders are found across Europe, North Africa, and parts of the Middle East and Asia. T. onustus reside in flowers in lowland vegetation. Females are distinguished by their larger size and ability to change color between white, yellow, and pink as a means of matching flower color. This cryptic mimicry allows them to both evade predators and enhance insect prey capture abilities. Males are smaller, more slender, and drab in coloration, usually green or brown. T. onustus is also distinguished from other relatives by its distinct life cycle patterns in which spiderlings emerge in either late summer or early spring. Furthermore, T. onustus have developed a mutualistic relationship with host plants where spiders feed on and/or deter harmful florivores while benefiting from the plant's supply of pollen and nectar, which T. onustus spiders are able to use as food sources, especially during periods of low insect prey abundance.

Sexual selection is described as natural selection arising through preference by one sex for certain characteristics in individuals of the other sex. Sexual selection is a common concept in animal evolution but, with plants, it is oftentimes overlooked because many plants are hermaphrodites. Flowering plants show many characteristics that are often sexually selected for. For example, flower symmetry, nectar production, floral structure, and inflorescences are just a few of the many secondary sex characteristics acted upon by sexual selection. Sexual dimorphisms and reproductive organs can also be affected by sexual selection in flowering plants.

Thomisus spectabilis, also known as the white crab spider or Australian crab spider, is a small spider found in Australia and far east Asia.

References

1 2 3 4 5 6 Rodrigues, Daniele (2018). "Do we truly understand pollination syndromes in Petunia as much as we suppose?". AoB Plants. 10 (5): ply057. doi:10.1093/aobpla/ply057. PMC 6202611 . PMID 30386543 . Retrieved 2022-12-02.
1 2 3 4 5 6 7 Guldberg, Larry D.; Atsatt, Peter R. (1975). "Frequency of Reflection and Absorption of Ultraviolet Light in Flowering Plants". The American Midland Naturalist. 93 (1): 35–43. doi:10.2307/2424103. ISSN 0003-0031. JSTOR 2424103.
1 2 3 Eugene Jones, C.; Buchmann, Stephen L. (1974-05-01). "Ultraviolet floral patterns as functional orientation cues in hymenopterous pollination systems". Animal Behaviour. 22 (2): 481–485. doi:10.1016/S0003-3472(74)80047-3. ISSN 0003-3472.
1 2 3 4 5 6 Koski, Matthew H.; Ashman, Tia-Lynn (August 2014). Campbell, Diane (ed.). "Dissecting pollinator responses to a ubiquitous ultraviolet floral pattern in the wild". Functional Ecology. 28 (4): 868–877. Bibcode:2014FuEco..28..868K. doi: 10.1111/1365-2435.12242 .
1 2 3 4 5 Finnell, Lindsay M.; Koski, Matthew H. (November 2021). "A test of Sensory Drive in plant–pollinator interactions: heterogeneity in the signalling environment shapes pollinator preference for a floral visual signal". New Phytologist. 232 (3): 1436–1448. doi: 10.1111/nph.17631 . ISSN 0028-646X. PMID 34287921. S2CID 236157784.
1 2 3 4 5 6 7 8 9 Gantz, G.M.; Sumner, W.G. (March 1957). "Stable Ultraviolet Light Absorbers". Textile Research Journal. 27 (3): 244–251. doi:10.1177/004051755702700310. ISSN 0040-5175. S2CID 138533333.
1 2 3 4 Klomberg, Yannick (2019). "The role of ultraviolet reflectance and pattern in the pollination system of Hypoxis camerooniana". academic.oup.com. Retrieved 2022-12-02.
1 2 3 Papiorek, S.; Junker, R. R.; Alves-dos-Santos, I.; Melo, G. A. R.; Amaral-Neto, L. P.; Sazima, M.; Wolowski, M.; Freitas, L.; Lunau, K. (January 2016). Dafni, A. (ed.). "Bees, birds and yellow flowers: pollinator-dependent convergent evolution of UV patterns". Plant Biology. 18 (1): 46–55. Bibcode:2016PlBio..18...46P. doi: 10.1111/plb.12322 . PMID 25703147.
↑ Miller, Renee; Owens, Simon J.; Rørslett, Bjørn (2011-03-01). "Plants and colour: Flowers and pollination". Optics & Laser Technology. Colour and Design II: Colour in plants and animals - Inspiration for Design. 43 (2): 282–294. Bibcode:2011OptLT..43..282M. doi:10.1016/j.optlastec.2008.12.018. ISSN 0030-3992.
1 2 3 4 5 Mori, Shinnosuke; Fukui, Hiroshi; Oishi, Masanori; Sakuma, Masayuki; Kawakami, Mari; Tsukioka, Junko; Goto, Katsumi; Hirai, Nobuhiro (2018-06-01). "Biocommunication between Plants and Pollinating Insects through Fluorescence of Pollen and Anthers". Journal of Chemical Ecology. 44 (6): 591–600. Bibcode:2018JCEco..44..591M. doi:10.1007/s10886-018-0958-9. ISSN 1573-1561. PMID 29717395. S2CID 254656409.

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[:0-1] 1 2 3 4 5 6 Rodrigues, Daniele (2018). "Do we truly understand pollination syndromes in Petunia as much as we suppose?". AoB Plants. 10 (5): ply057. doi:10.1093/aobpla/ply057. PMC 6202611 . PMID 30386543 . Retrieved 2022-12-02.

[:1-2] 1 2 3 4 5 6 7 Guldberg, Larry D.; Atsatt, Peter R. (1975). "Frequency of Reflection and Absorption of Ultraviolet Light in Flowering Plants". The American Midland Naturalist. 93 (1): 35–43. doi:10.2307/2424103. ISSN 0003-0031. JSTOR 2424103.

[:2-3] 1 2 3 Eugene Jones, C.; Buchmann, Stephen L. (1974-05-01). "Ultraviolet floral patterns as functional orientation cues in hymenopterous pollination systems". Animal Behaviour. 22 (2): 481–485. doi:10.1016/S0003-3472(74)80047-3. ISSN 0003-3472.

[:3-4] 1 2 3 4 5 6 Koski, Matthew H.; Ashman, Tia-Lynn (August 2014). Campbell, Diane (ed.). "Dissecting pollinator responses to a ubiquitous ultraviolet floral pattern in the wild". Functional Ecology. 28 (4): 868–877. Bibcode:2014FuEco..28..868K. doi: 10.1111/1365-2435.12242 .

[:4-5] 1 2 3 4 5 Finnell, Lindsay M.; Koski, Matthew H. (November 2021). "A test of Sensory Drive in plant–pollinator interactions: heterogeneity in the signalling environment shapes pollinator preference for a floral visual signal". New Phytologist. 232 (3): 1436–1448. doi: 10.1111/nph.17631 . ISSN 0028-646X. PMID 34287921. S2CID 236157784.

[:8-6] 1 2 3 4 5 6 7 8 9 Gantz, G.M.; Sumner, W.G. (March 1957). "Stable Ultraviolet Light Absorbers". Textile Research Journal. 27 (3): 244–251. doi:10.1177/004051755702700310. ISSN 0040-5175. S2CID 138533333.

[:5-7] 1 2 3 4 Klomberg, Yannick (2019). "The role of ultraviolet reflectance and pattern in the pollination system of Hypoxis camerooniana". academic.oup.com. Retrieved 2022-12-02.

[:6-8] 1 2 3 Papiorek, S.; Junker, R. R.; Alves-dos-Santos, I.; Melo, G. A. R.; Amaral-Neto, L. P.; Sazima, M.; Wolowski, M.; Freitas, L.; Lunau, K. (January 2016). Dafni, A. (ed.). "Bees, birds and yellow flowers: pollinator-dependent convergent evolution of UV patterns". Plant Biology. 18 (1): 46–55. Bibcode:2016PlBio..18...46P. doi: 10.1111/plb.12322 . PMID 25703147.

[9] Miller, Renee; Owens, Simon J.; Rørslett, Bjørn (2011-03-01). "Plants and colour: Flowers and pollination". Optics & Laser Technology. Colour and Design II: Colour in plants and animals - Inspiration for Design. 43 (2): 282–294. Bibcode:2011OptLT..43..282M. doi:10.1016/j.optlastec.2008.12.018. ISSN 0030-3992.

[:7-10] 1 2 3 4 5 Mori, Shinnosuke; Fukui, Hiroshi; Oishi, Masanori; Sakuma, Masayuki; Kawakami, Mari; Tsukioka, Junko; Goto, Katsumi; Hirai, Nobuhiro (2018-06-01). "Biocommunication between Plants and Pollinating Insects through Fluorescence of Pollen and Anthers". Journal of Chemical Ecology. 44 (6): 591–600. Bibcode:2018JCEco..44..591M. doi:10.1007/s10886-018-0958-9. ISSN 1573-1561. PMID 29717395. S2CID 254656409.

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