Beauty is in the eye of the beholder—even for lizards

What is it about?

How important are colors that humans cannot see? In an article published in Proceedings of the National Academy of Sciences (USA), a research team—led by scientists from CIBIO/InBIO (University of Porto), the University of Valencia, and Uppsala University—reveals the evolutionary mysteries of ultraviolet colors in lizards. Wall lizards are one of the most widespread reptiles across Europe. These little reptiles have been studied for decades because of their outstanding diversity in colors. However, scientists weren’t seeing all of it. One team of researchers discovered very recently that wall lizards with white bellies actually represented two clearly different colors: a difference that was only seen under ultraviolet (UV) light. But how come this variation went unnoticed for so long? Under the visible light humans cannot appreciate differences in the UV but, crucially, many animals do. While we cannot tell them apart, UV signals play a key role in animal interactions, including fighting and social signaling. To understand how wall lizards evolved this hidden diversity, the team of researchers sequenced the genomes of lizards with differences in UV coloration. Their findings revealed that genetic mutations near a single gene involved in pigment cell development explained the difference. The scientists then studied lizard skin cells in detail, finding that these genetic mutations impacted only a single type of cell. Specifically, the skin cells that harbor colorful pigments become insufficiently developed, leading to animals carrying these mutations in their DNA having a different color to others of its species. But while the scientists initially discovered this difference in lizards that appear white-bellied to the naked human eye, how do the other colors fit into the story? For over a century, wall lizards have been famous among biologists for their striking orange, yellow and white bellies, and have helped researchers formulate hypothesis on how and why animals communicate. According to researchers, the new results show that the same genetic change that affects UV coloration in white lizards can also prevent the other colors from even forming in the first place, making them effectively invisible not only to us humans but to the lizards themselves.

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Photo by Adrien Stachowiak on Unsplash

Photo by Adrien Stachowiak on Unsplash

Why is it important?

These findings shed a unique light on animal communication, historically dominated by studies on bright colorful animals. By showing the importance of studying animal colors from the perspective of animals themselves researchers discovered genes and cells responsible for UV coloration. These findings suggest that many other important aspects of animals’ biology may have been overlooked by focusing on traits that we can detect, opening fresh perspectives for future research.