Distinct patterns on the skin of ocellated lizards are determined by a cellular automaton, a simple rule-based model that is normally associated with computer science, according to a study in Nature this week. An analysis of changing colour dynamics in lizards, from new-born to adult, reveals that these markings are produced in a different way from those seen on other animals, such as zebras and leopards.
At birth, the ocellated lizard (Timon lepidus) has brown skin speckled with white dots, but by the time the lizard reaches adulthood this pattern has transformed into a green and black labyrinthine pattern. To understand how these colour patterns develop, Michel Milinkovitch and colleagues used a high-resolution robotic system to scan three male individuals at multiple time points from the age of two weeks to three to four years. Unlike many animals, in which colour patterns are determined by interactions within individual cells, the authors find that in the ocellated lizard the colour of one scale is determined by that of its neighbours. They describe this process as a living cellular automaton. In the world of computing, a cellular automaton consists of connected units whose individual behaviour depends on the states of its neighbouring units.
The authors observe about 1,500 dorsal scales change colour during a period of four years. These colours change throughout life, although the rate of colour change slows with age. The authors suggest that the labyrinthine pattern of green and black scales seen in adults could potentially serve as camouflage and might be involved in sexual selection.