To be seen or to be understood: the evolutionary dilemma of iridescent colors

In nature, color is never merely an aesthetic matter, but a biological adaptation. From the iridescent wings of a butterfly to the understated green of a leaf, from the vibrant colors of a flower to the brown tones of a viper, hues fulfill essential functions linked to the survival of both the individual and the species. Through color, organisms can communicate, warn, seduce, or camouflage themselves, especially in contexts related to reproduction or predation.

However, if we look closely at the living world, a curious paradox emerges. Despite the enormous chromatic diversity present in many species, iridescent colors—those that change hue depending on the angle of light and the viewer's perspective—are relatively rare. Yet, they have evolved in very different groups of organisms, from insects to birds, octopuses, tropical fish, flowers, and even some fruits. Why does nature resort to these striking and brilliant visual effects in some species, while seemingly avoiding them in many others? A work published in Science Advances The sociobiologist Casper J. van der Kooi and his collaborators at the University of Würzburg, Germany, offer an elegant answer based on a visual compromise between the visibility they provide and the reliability of the signal they transmit.

They act as a visual beacon

Most of the colors we see in nature are dull and inconspicuous. We often don't realize this because our attention is focused on the bright colors, but these are clearly in the minority. Furthermore, dull colors are remarkably stable: a yellow flower, a red feather, or the skin of an amphibian maintains the same color from almost any viewing angle. This consistency is key for this property to function as a reliable signal: a pollinator, a potential mate, or a breeding partner must be able to recognize the message quickly and unambiguously.

Iridescent colors, on the other hand, behave differently. They depend on the angle of incidence of the light, the viewing distance, and the movement of the organism, generating intense but ever-changing flashes. This makes them spectacular, but also potentially confusing.

In their study, these researchers analyzed how some insects perceive these colors and demonstrated that their variability is not an accidental flaw, but rather the result of an evolutionary compromise. Using artificial flowers observed by bumblebees, insects in the Apidae family, like honeybees, they found that bumblebees are able to detect shiny surfaces from a much greater distance than matte ones. Specular reflections act like a visual beacon, comparable to a flashing beam that stands out against the relatively homogeneous background of the landscape.

This ability can be crucial in environments where finding a flower or a mate is difficult and time is limited. However, the same brightness that facilitates long-distance detection comes at a price. When bumblebees approach the flower, the intense reflections interfere with their perception of the surface's natural color. At close range, the color signal becomes less reliable. What was a powerful attractant from afar can become an ambiguous stimulus up close.

Rare in nature

This functional paradox helps explain why iridescent colors are rare in nature, yet have evolved independently in many different lineages. Dynamic visual effects, such as brightness or iridescence, have been described in flowers, insects, birds, fish, and even some fruits. Their origin lies not so much in special pigments as in the physical structure of surfaces. At the microscopic scale, they depend on thin layers and periodic reliefs formed by nanostructures that manipulate light and generate intense reflections.

This structural coloration possesses a key property: it can greatly amplify visibility without altering the base color. In the case of flowers, it allows them to attract pollinators from afar without changing the chromatic signal they use to recognize a specific species. The price to pay is the loss of signal reliability at close range, a cost that is only worthwhile in certain ecological contexts. Therefore, natural selection favors shiny surfaces only when the benefit of being seen outweighs the risk of being misinterpreted.

The authors propose that this balance explains both the rarity and the scattered distribution of bright and iridescent colors. It is not a universal solution, but rather a specialized strategy, particularly useful in open and well-lit environments. In darker or denser environments, on the other hand, the consistency of matte colors proves much more effective.

Beyond evolutionary biology, these results have relevant implications for technology and design. Understanding how nature uses shiny surfaces to make itself more detectable can inspire new materials, visual signals, or lighting systems based on dynamic effects. In fact, biomimetics It is already exploring how these structures can contribute to the development of new smart displays, sensors, and coatings.