Why does life continue to evolve these geometric patterns?

A global catalog shows how creatures from the tree of life balance rigidity and flexibility in a remarkably consistent way.

By Anirban Mukhopadhyay edited by Sarah Lewin Frasier

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The mirror spider can quickly move a patchwork of tiny reflective plates beneath the outer surface of its abdomen, changing the pattern of mirror-like flashes. This unusual display comes from common staples: similar tile-like arrangements flexible plates and joints appear throughout the tree of life, from turtle shells to tropical fruit peels. Researchers have now compiled 100 examples of this pattern in animals, plants, microbes and viruses, which they describe In Nexus PNAS.

Study co-author Mason Dean, a biologist at the City University of Hong Kong, was the first to notice a regular mosaic pattern in micro-computed tomography scans of a ray skeleton. He was surprised to find that what looked like a pixelated grain was actually a mosaic of tiny hexagons and pentagons arranged edge to edge across the cartilage. Jana Ciecierska-Holmes, a zoologist at Humboldt University in Berlin, also a co-author, began looking for examples of tiles and was also surprised to spot complex, interlocking plates on the outer coating of millet seeds. They and their colleagues sought to determine how widespread these tiling designs were.

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The researchers focused on true tilings, in which geometric tiles are discrete structural pieces separated by smoother seams, rather than purely visual or hollow patterns such as animal colorings or honeycombs. To compare such systems in very different organisms, they created a framework describing what different natural tiles are made of, how they are shaped, how they connect, and what they do. The results reveal structural parallels between many organisms without any common ancestry.

Chitons evolved articulated shell plates, while sharks evolved tessellated cartilage — two tiled structures that arose independently in distant evolutionary lineages, the researchers found — and microscopic amoebae construct architecturally similar protective coverings from scavenged mineral tiles. Other variations cover the lenses of insect eyes and form corky patch patterns in the sole of the elephant foot. Across all kingdoms, the same basic arrangement helps animals see, move, and protect their bodies.

Recurrence reflects how geometry and growth push organisms toward the same solutions. Predominantly six-sided patterns, like those of sharks and rays, are a classic way to effectively cover curved surfaces, for example. Dean also notes that the borders of the tiles often align with regions where new cells are added during growth, allowing the tissues to function as they develop. Additionally, the combination of hard tiles and softer joints balances rigidity and flexibility, adds Stanislav Gorb, a zoologist at the University of Kiel, who was not involved in the study. “A structure that is too rigid is good at resisting forces but bad at generating movement.”

The authors hope their online catalog becomes a living resource to help people recognize these patterns in the organisms and structures they study. “Once you start paying attention to it, you see it everywhere,” Dean says. Ciecierska-Holmes agrees: “You kind of enter the world of tessellation. »