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WOODS HOLE, Mass. -- Like invisibility in legends, transparency in nature is a powerful tool. Most transparent animals live in the ocean, where a close visual match with the water renders them almost invisible to predators.

On land, transparency is rare and difficult to achieve, but some butterflies and moths (Lepidoptera) do have transparent wings. And a  indicates transparency can serve not only to camouflage them, but in other cases to signal and warn predators, 91�������לDon91�������יt eat me! I91�������יm toxic.91�������ם

This flexible weapon for self-defense is one of many findings from a multiyear study spanning the physics, biology, ecology, and evolution of transparency in Lepidoptera conducted by several groups, including the lab of , director of the Marine Biological Laboratory (MBL).

91�������לThis is one of those interdisciplinary studies you dream about, where you want to understand [a biological structure] from its physics to its development and ecology,91�������ם says Patel of the international study, which began as a project in the MBL Embryology course and ended up being funded by the   Ph.D. candidate Aaron Pomerantz in Patel91�������יs lab is also on the team.

Mimicry for Self-Defense

The group91�������יs  adds a unique perspective on Lepidoptera self-defense. In some species, vivid wing coloration indicates the presence of chemical defenses that make the butterfly unpalatable or toxic, and predators learn to avoid them. Accordingly, palatable species can evolve to mimic the toxic ones, so predators leave them alone, too. In addition, multiple unpalatable species may converge in their warning colorations, thereby sharing in the benefits of the warning coloration process. Large 91�������לmimicry rings91�������ם can even form containing both toxic and nontoxic species, all displaying strikingly similar patterns and color combinations.

91�������לThe most amazing place to see this is the Amazon,91�������ם Patel says. 91�������לYou91�������יll find a group of species that are distantly related to each other, yet they91�������יve all converged on a similar wing pattern.91�������ם

Surprisingly, mimicry rings have also been found among clear-wing species in the Amazon. 91�������לSo we asked, 91�������טWait, why would a species be transparent and unpalatable at the same time?91�������י91�������ם Patel says. And, structurally, how would a clear-wing species accomplish that trick?

The team looked at the optical and structural properties of transparent butterfly wings within mimicry rings to see if they were convergent, and found in some rings, they were.

91�������לIn one transparency ring we studied (see top photo, middle row), the key unpalatable butterfly doesn91�������יt have an anti-glare coating on its transparent wing, so in sunlight, it91�������יs really easy to see,91�������ם Patel says. 91�������לIt may be signaling a warning pattern to predators when it91�������יs in bright sun, and it91�������יs camouflaged when in shadows. So it kind of cheats: it has the best of both worlds.91�������ם

Previously, the team reported on the developmental origins of transparency in a clear-wing species, Greta oto. They also  for its structural basis, optical properties, and biological relevance in relation to concealment, thermoregulation, and protection against UV. Those results showed a wide diversity of solutions to achieve transparency, suggesting that transparency has likely evolved multiple times independently.

Approaching transparency from multiple disciplines brought emergent knowledge and interesting new questions, Patel said. 91�������לNow that we91�������יve identified different Lepidoptera groups that have found different ways to achieve transparency, we can ask, how did they actually do this? Or, alternatively, if two very distant lineages have come up with the same solution for transparency, did they solve the problem in the same way?91�������ם

In addition to the MBL, collaborators in the initiative include scientists from the University of California, Berkeley; University of Chicago; California Institute of Technology; CNRS, France; Muséum National d91�������יHistoire Naturelle, France; Sorbonne Université, Paris, France; Université des Antilles, France; Ecole Pratique des Hautes Etudes, France; Ministère de la Culture, France; and Université de Montpellier, France.

Citations:

Pinna, C., et al. (2021). Mimicry can drive convergence in structural and light transmission features of transparent wings in Lepidoptera. 

Gomez D., et al (2021). Transparency in butterflies and moths: structural diversity, optical properties and ecological relevance. Ecological Monographs, e01475. 

Pomerantz AF, et al (2021). Developmental, cellular, and biochemical basis of transparency in the glasswing butterfly Greta oto. J Exp Biol 224, jeb237917. 

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The Marine Biological Laboratory (MBL) is dedicated to scientific discovery 91�������ד exploring fundamental biology, understanding marine biodiversity and the environment, and informing the human condition through research and education. Founded in Woods Hole, Massachusetts in 1888, the MBL is a private, nonprofit institution and an affiliate of the .