What Causes Tigers to Have a Certain Pattern of Stripes

What causes zebras or tigers to have a certain pattern of stripes? Scientists have taken a closer look at these natural patterns and have assembled a range of models into a single equation to determine what variables control stripe formation in living things.

"We wanted a very simple model in hopes that it would be a big picture enough to include all of these different explanations," said Tom Hiscock, one of the researchers, in a news release. "We now get to ask what is common among molecular, cellular, and mechanical hypotheses for how living things orient the directions of stripes, which can then tell you what kinds of experiments will (or won't) distinguish between them."

Stripes are surprisingly simple to model mathematically. These patterns emerge when interacting substances create waves of high and low concentrations of, for example, a pigment, chemical, or type of cell. However, Turing's model, which explains stripes, doesn't explain how they orient themselves in one particular direction.

In this latest study, the researchers looked at why tiger stripes are horizontal. They found that it actually takes only a small change to the model to switch whether the stripes are vertical or horizontal. What researchers don't know is how this translates to living things.

The researchers eventually created a master model that predicts three main perturbations that can affect how stirpes orient. One is a change in the "production gradient," would be a substance that amplifies stripe pattern density. The second is a change in "parameter gradient," which is a substance that changes one of the parameters involved in forming the stripe. The last is a physical change in the direction of the molecular, cellular, or mechanical origin of the stripe.

The findings are based in theory, but could be used to determine whether the math holds true in living systems.

The findings are published in the journal Cell Systems.

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