Pigmentation in some Butterfly Wings created by Nanostructures
ScienceDaily (Jan. 22, 2008) - Nowhere in nature is there so much beautiful colour as on the wings of butterflies. Scientists, however, are still baffled about exactly how these colours are created. Marco Giraldo has been examining the structure of the surface of the wings of the cabbage white and other butterflies. Among the things he has discovered is why European cabbage whites are rebuffed more often than Japanese ones. Giraldo will be awarded a PhD by the University of Groningen on 25 January 2008.
The colours on butterfly wings are used as an advertisement. The patterns on the wings enable butterflies to recognize their own species at a distance and differentiate between males and females - rather handy when you're hunting for a partner. Just like a pointillist painting, the surface of the wing is constructed of a huge collection of coloured dots, called scales, each about 50 x 250 micrometers in size.
However, scientists don't yet know very much about how the colour on the wings is formed. What they do know is that the colours are created in two different ways: via pigments and via nanostructures on the scales, which ensure that light is distributed in ways that are sometimes spectacular. These so-called structure colours can clearly be seen on the morpho butterflies of the South American rainforests.
Marco Giraldo examined the structure and the pigments of the wings of the cabbage white and other Whites from the Pieridae family. The physicist chose the Whites because they have relatively simple pigmentation. By comparing the scales of various sorts under an electron microscope, he discovered how the colouration of Whites is caused. Giraldo is the first to clarify how the colour of these butterflies is influenced by the nanostructural characteristics.
Although the spatial structure of a scale depends on the type of butterfly, there are a number of general characteristics: A scale consists of two layers, linked by pillars. The undersurface is virtually smooth and without structure, but the upper surface is formed by a large number of elongated, parallel ridges, about one to two micrometers from each other. The colour is determined by the dispersal of light by the scale structures and by the absorption of light by any pigments present. The pigments of the cabbage white, for example, absorb ultraviolet light and the brimstone blue light. At the same time they also scatter white or yellow light respectively.
Giraldo also discovered that the wings of Whites are constructed in a surprisingly effective way. Both sides of the wings have two layers of overlapping scales that reflect light. The more scales there are, the more light is reflected. This light reflection is very important as butterflies want to be seen. Giraldo discovered that these two layers form an optimal construction: with more than two layers the reflection may be improved, but the wing would become disproportionately heavy.
Giraldo has also discovered why Japanese male cabbage whites are better at recognizing females than European cabbage whites, who still make mistakes in this area. This is because the wings of Japanese male and female cabbage whites differ subtly, unlike those of their European relatives: the scales on the wings of Japanese female cabbage whites lack specific pigment grains, those that ensure that UV light is absorbed. Males do have these pigment grains, as do both sexes of the European cabbage whites. This difference makes it easier for Japanese male cabbage whites, who unlike humans can see UV light, to differentiate between males and females.
New colour methods can be developed using the knowledge derived from Giraldo's research. It may be possible to apply the nanostructures observed in butterflies to create impressive optic effects in paint, varnish, cosmetics, packaging materials and clothes. Industry is thus following butterfly wing research with great interest.
Butterflies Use Polarized Light To Attract Mates
ScienceDaily (May 1, 2003) - Up to 20 layers of transparent scales on butterfly wings scatter white light to produce brilliant blue structural color. Alison Sweeney, Duke University, and collaborators at the Smithsonian Tropical Research Institute report in Nature that polarized light from iridescent female Heliconius butterflies functions as a mating signal. This may be the first example of mate recognition based on polarized light. Physical properties of wing scales may play an important role in speciation of Heliconius butterflies.
People in small planes flying low over tropical forest often comment about the tiny flashes of blue from iridescent butterfly wings that stand out against dark green jungle foliage. But the ecological significance of light scattering and shaping by butterflies has, for the most part, been overlooked.
Sweeney brings a new emphasis on the physical properties of butterfly wings to a group studying the genetics and ecology of speciation in Heliconius butterflies. She presented moving female butterfly wings to conspecific males with and without filters that eliminate polarized light. Males of an iridescent species approached females producing polarized signals significantly more often when signals were not depolarized. Males of another, non-iridescent species approached females, which do not produce polarized signals, at the same rate regardless of the presence or absence of the depolarizing filters.
Differences in light bending by genetically inherited patterns of butterfly scales may be important in sexual selection and speciation of Heliconius butterflies and may vary according to the specific light environment they occupy in tropical forests.
Ref. Alison Sweeney, Christopher Jiggins, Sonke Johnsen. Polarized light as a butterfly mating signal. Nature. 1 May, 2003.
The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is one of the world?s leading centers for research on the ecology, evolution and conservation of tropical organisms.
Secrets Behind Butterfly Wing Patterns Uncovered
ScienceDaily (Oct. 26, 2007) - The genes that make a fruit fly's eyes red also produce red wing patterns in the Heliconius butterfly found in South and Central America, finds a new study by a UC Irvine entomologist.
Bob Reed, assistant professor of ecology and evolutionary biology, discovered that genes involved in making insect eye pigments evolved over time to also make wing pigments in butterflies. This finding sheds light on the genetic causes of wing patterns and why, in the Heliconius, those patterns can vary widely from region to region.
"We found that evolution is achieved primarily through recycling old genes into new functions, as opposed to evolving entirely new genes from scratch," Reed said.
Within one species of the butterfly genus Heliconius, more than 20 distinct wing patterns can exist in different geographic regions. Over time, the Heliconius evolves to look like local unrelated butterfly species that are poisonous to birds, a phenomenon called mimicry.
"It is a very basic textbook example of natural selection," Reed said. "If you look like you're poisonous, you're not going to get eaten and you can produce offspring."
Reed's study also explains under which conditions certain genes will cause a stripe on a Heliconius wing to become yellow or red.
W. Owen McMillan of the University of Puerto Rico and Lisa M. Nagy of the University of Arizona also worked on this study, which was funded by the National Science Foundation and a University of Arizona IGERT genomics fellowship.
UC Irvine has two additional butterfly experts - Adriana Briscoe, who studies butterfly eyes and color vision, and Tony Long, who studies eyespot patterns on butterfly wings. All three scientists are members of the Department of Ecology and Evolutionary Biology in the School of Biological Sciences.
Results of the study appeared online in the Proceedings of the Royal Society B.
The Butterfly Conservatory: FAQ
1: What's the difference between a butterfly and a moth?
2: Do butterflies have any of our five senses?
3: How do butterflies communicate?
4: Do butterflies sleep?
5: How do butterflies reproduce?
6: How long do butterflies live?
7: Do butterflies migrate?
8: What makes butterfly wings colorful?
9: Are butterflies endangered? Are any extinct?
10: How small is the smallest butterfly, and how big is the biggest?
Adonis Blue (Male)
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