Turing Patterns in Animal Coats: Turing Patterns in Animal Coats Junping Shi Alan Turing (1912-1954): Alan Turing (1912-1954) One of greatest scientists in 20th century
Designer of Turing machine (a theoretical computer) in 1930’s
Breaking of U-boat Enigma, saving battle of the Atlantic
Initiate nonlinear theory of biological growth
http://www.turing.org.uk/ James Murray (author of books: Mathematical Biology): James Murray (author of books: Mathematical Biology) Emeritus Professor
University of Washington, Seattle
Oxford University, Oxford
http://www.amath.washington.edu/people/faculty/murray/ Murray’s theory: Murray’s theory Murray suggests that a single mechanism could be responsible for generating all of the common patterns observed. This mechanism is based on a reaction-diffusion system of the morphogen prepatterns, and the subsequent differentiation of the cells to produce melanin simply reflects the spatial patterns of morphogen concentration.
Melanin: pigment that affects skin, eye, and hair color in humans and other mammals.
Morphogen: Any of various chemicals in embryonic tissue that influence the movement and organization of cells during morphogenesis by forming a concentration gradient. Murray’s Theory (Cont.): Murray’s Theory (Cont.) The development of color pattern on the skin of mammal occurs
towards the end of embryogenesis, but it may reflect an underlying
pre-pattren that is laid down much earlier. (For zebra, the pre-pattern is
formed around 21-35 days, and the whole gestation peirod is about 360
days.) To create the color patterns, certain genetically determined cells,
called melanoblasts, migrate over the surface of the embryo and
become specialised pigment cell, called melanocytes. Hair color comes
from the melanocytes generating melanin, within the hair follicle, which
then pass into the hair. From experiments, it is generally agreed that
whether or not a melanocyte produces melanin depends on the
presence of a chemical, which we do not know.
Slide6: Reaction-diffusion systems Domain: rectangle
head and tail (no flux),
body side (periodic) Slide7: The full reaction-diffusion system: Solution of the system: Slide9: “Theorem 1”: Snakes always have striped (ring) patterns, but not spotted patterns.
Turing-Murray Theory: snake is the example of b/a is large. Snake pictures (stripe patterns): Snake pictures (stripe patterns) Slide11: “Theorem 2”: There is no animal with striped body and spotted tail, but there is animal with spotted body and
Turing-Murray theory: The body is always wider than the tail. The same reaction-diffusion mechanism should be responsible for the patterns on both body and tail. Then if the body is striped, and the parameters are similar for tail and body, then the tail must also be striped since the narrower geometry is easier to produce strips.
Examples: zebra, tiger (striped body and tail), leopard (spotted body and tail), genet, cheetah (spotted body and striped tail) Spotted body and striped tail or legs: Spotted body and striped tail or legs Cheetah (upper), Okapi (lower) Tiger (upper), Leopard (lower) Spotted body and striped tail: Spotted body and striped tail Genet (left), Giraffe (right) Tail patterns of big cats: Tail patterns of big cats Domain: tapering cylinder, with the width becoming narrower at the end.
We still use no-flux boundary condition at the head and tail parts, and periodic boundary condition on the side.
Predicted patterns: spots on the wider part, and strips on the tail part; all spots; or all strips. Slide15: (a) (b) (c) Numerical simulations
(d) Cheetah tail markings
(e) Jaguar tail markings
(f) Genet tail markings
(g) Leopard tail markings Leopard: the spots almost reach the tip of tail, the pre-natal leopard tail is sharply tapered and relatively short; There are same number of “rings” on the pre-natal and post-natal tails; the sharply tapered shape allow the existence of spots on top part of tail; larger spots are further down the tail,
and the spots near the body are relatively small.
Genet: uniformly striped pattern; the genet embryo tail has a remarkably uniform diameter which is relatively thin. Natural Patterns of cos(kx): Natural Patterns of cos(kx) cos(x): Valais goat
(single color: f(x)=1, a lot of examples) Slide17: Cos(2x): Galloway belted Cow Slide18: cos(2x): Giant Panda Effect of scale on pattern: Effect of scale on pattern very small domain: lambda is small, there is no spatial pattern, and the constant is stable. (small animals are uniform in color: squirrel, sheep, small dogs) medium size domain: lambda is not too large nor too small, and there are many spatial patterns. (zebra, big cats, giraffe) large domain: lambda is large, and there are patterns but the structure of the pattern is very fine. (elephant, bear) small black cat
elephant Other related researches: Other related researches Patterns of sea shells Patterns of tropical fishes