How did the tiger get its stripes? is answered in the Vietnamese folk tale. Hoping to acquire wisdom the tiger ends up with stripes instead.

How did the zebrafish get its stripes?  is answered by researchers at the University of Bath.

Zoom into the zebrafish’s alternating pattern and the stripes of colour resolve into individual pigment cells like a pointillist painting. credit: Adapted by Kit Yates from Wikimedia and inset by Jennifer Owen

Zebrafish are freshwater fish belonging to the minnow family. They are native to South Asia but are popular fish for aquariums.

The stripes of an adult ‘wild type’ zebrafish are formed from pigment-containing cells called chromatophores. There are three different types of chromatophore in the fish, and as the animal develops, these pigment cells shift around on the animal’s surface, interacting with one other and self-organising into the stripy pattern for which the fish are named. Occasionally, mutations appear, changing how the cells interact with each other during pattern development resulting in spotty, leopard-skin or maze-like labyrinthine markings.

Biologists have studied the biological interactions needed for the self-organisation of a zebrafish’s pigment cells. Now mathematicians at Bath have developed a mathematical model that incorporated the three cell types and all their known interactions  to explain how these patterns form.

Dr Kit Yates, the mathematician from Bath who led the study, said:

“It’s fascinating to think that these different pigment cells, all acting without coordinated centralised control, can reliably produce the striped patterns we see in zebrafish.

“Our modelling highlights the local rules that these cells use to interact with each other in order to generate these patterns robustly.”

Now as well as being fascinating in itself the mathematical modelling has wider implications which will benefit other areas of research.

 Professor Robert Kelsh, co-author of the study said:

“These stripes are an example of a key developmental process. If we can understand what’s going on in the pattern development of a fish embryo, we may be able to gain deeper insight into the complex choreography of cells within embryos more generally.”

Pattern formation is an important general feature of organ development. A better understanding of pigment pattern formation might give us insights into diseases caused by disruption to cell arrangements within organs.

The model has proven successful, predicting the pattern development of both wild type and mutant fish.

Jennifer Owen, the scientist responsible for building and running the model, said:

“One of the benefits of our model is that, due to its complexity, it can help to predict the developmental defects of some less understood mutants. For example, our model can help to predict the cell-cell interactions that are defective in mutants such as leopard, which displays spots.”

And just to clear up the question that started this article:

Reporter: Fiona Grahame