According to foreign media reports, many animals have evolved camouflage "tactics" in self-defense, but some butterflies and moths have even gone further. They have evolved transparent wings that make them almost invisible to predators. A team led by scientists at the Marine Biology Laboratory (MBL) studied the development of such a species, the glass-winged butterfly Greta oto, to uncover the secrets of this natural "stealth technology." Their work was published in the Journal of Experimental Biology.
Although the transparent structure of animals has been confirmed, they appear more often in aquatic organisms. "It's an interesting biological question because there aren't as many transparent organisms on land," noted study lead author Aaron Pomerantz, a doctoral student in integrative biology at the University of California, Berkeley. "So we ask the question: What is the actual developmental basis for how they create transparent wings?"
Butterfly wings are known for their colorful patterns created by tiny, overlapping, chitinous scales that reflect or absorb light of various wavelengths to produce color. Pomerantz said that despite in-depth research into scale coloring, investigations into the developmental origins of the transparency of terrestrial butterflies have not been done before. "Transparency is a bit like the opposite side of color," he said. ”
Pomerantz and his co-authors, including his doctoral supervisor and MBL director Nipam Patel, were inspired by the work of students in MBL's embryology program. "I decided to bring some of my collection of transparent butterfly and moth species to the course and as a challenge for students to see how transparent these wings are," Patel said. Patel said: "A group of students solved this problem by imaging the wings with various microscopes. They realized that almost every way you could think of making the wings transparent, some butterflies or moths came up with a way. That's why let's look at transparent developments in more detail. ”
Building on this work, the researchers used confocal and scanning electron microscopy to construct a developmental timescale of how transparency occurs in Greta oto, from pupal stage to adulthood. They found that the wings of the glass-winged butterfly developed differently from opaque species, later developing into transparent areas with lower densities of precursor scale cells. At very early stages, the growth and morphology of the scales are different, with thin, mane-like scales developing in transparent areas and flat, rounded scales in opaque areas.
"What Greta oto does is make fewer scales and make them into these very different, bristle-like shapes," Patel explains. "But getting the scales out is only part of creating the transparency problem." Aaron also made a series of observations of the nanostructures on the wings that protect against glare in bright sunlight. "When light hits small arrays of these nanostructures, it doesn't reflect, it passes directly through. So it provides better transparency," he said.
"As humans, we think we're smart because we figured out how to apply an anti-glare coating to glass, but butterflies basically figured out that way tens of millions of years ago," Patel said. ”
Unusual wing scales and nanostructures are just part of the story. A second layer of waxy hydrocarbon nanotubes is located on the surface of the wings, providing further anti-reflective properties. The researchers examined the reflectivity of the wings before and after removing the waxy layer with n-hexane.
"We measured the amount of light reflected from the wings," Pomerantz said. "These experiments show that the upper layers are very important to help reduce glare. Biochemical analysis showed that the waxy layer consists mainly of long-chain n-alkanes, similar to the waxy layer found in other insect species. They are mainly thought to be things that help prevent insects from drying out or drying out. But in this case, it seems that they are also used for these anti-glare properties. "
Future research directions may include a more in-depth study of how these transparent structures have evolved. Pomerantz notes, "If we can learn more about how nature creates new types of nanostructures, this will be very enlightening for human applications." ”