Skin colour patterns in fishes, amphibians and reptiles are self-organised through interactions among three types of chromatophore cells. Surprisingly, multiple species of lizards exhibit a scale-by-scale colour pattern, some scales being black and other being green or yellow. Even more surprisingly, many scales switch from green/yellow to black and from black to green/yellow during the life of the animal. In a new Article in Current Biology, we investigate this phenomenon using multiple mathematical models and show that reaction-diffusion (RD), developed in 1952 by Alan Turing, is particularly efficient in predicting those patterns.
In this new publication, Ebrahim Jahanbakhsh and Michel Milinkovitch in the Laboratory of Artificial & Natural Evolution (LANE) show that five divergent species of lizards have independently evolved dynamics of scale-by-scale skin colour patterning. These dynamics emerge from the superposition of the bumpy skin geometry (because of the presence of scales) with the self-organised segregation of chromatophore cells. The researchers further demonstrate that Reaction-Diffusion, Cellular Automaton and Lenz-Ising models predict, in all species, the statistical features of the patterns despite their substantially-different motifs, whereas Reaction-Diffusion better predicts exact scale-by-scale colours. Finally, Jahanbakhsh and Milinkovitch show that residual scale-by-scale error is entirely explained by uncertainties in skin geometry and in colour measurements at the juvenile stage, making Reaction-Diffusion remarkably performant without the need to parametrise the profusion of variables at the nanoscopic and microscopic scales.
Please, check the original article for details:
Modelling Convergent Scale-by-Scale Skin Colour Patterning in Multiple Species of Lizards
Ebrahim Jahanbakhsh & Michel C. Milinkovitch*
Current Biology 32, 1-14, December 5, 2022