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 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. We 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, we 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 (23), 5069-5082.e13 (2022)