Thursday, December 1, 2016

Spots versus Stripes

Spots versus Stripes

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zebras Spots versus Stripes

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For years the fashion industry has been obsessed by spots and stripes. With inspiration for these patterns taken no doubt from nature; fashionable black and white stripes from the zebra for example, and spots from the coat of the leopard.

In fact, there are examples of spots and stripes covering many creatures, some of which retain their spotty or stripy pattern throughout their life; some that impressively change their pattern from stripes to spots as they grow into adulthood, like the impressive zebra shark (also known as the leopard shark); and some who are covered in both, such as the Brazilian tapir.

The development of these patterns in nature is not happening by accident. Alan Turing, famous for cracking the Enigma code that helped to end the Second World War, recently has had substance added to his 1950s theory around pattern formation, going some way to explaining how spots and stripes appear in nature.

His paper provided the foundations for research demonstrating that patterns are formed by the different rates of diffusion between an interacting of a pair of chemicals; one of which activates cell growth and the other of which inhibits the process. It is thought that this start-stop activity created by the inhibitor diffusing faster than the activator is behind the development of all repeated patterns in nature. This extends from the spots on the back of a ladybird to the number of spikes on a hedgehog, the arrangement of the floret on a cauliflower and even the number and spacing of hair follicles.

Computer calculations that took place in the early 70s demonstrated that this system creates two perfect types of pattern – spots and stripes, and any variations of these patterns are created by random defects. So why does a leopard never change its spots, a tiger never change its stripes, whereas a zebra shark’s pattern changes during its life?

This can be explained by genetics. The gene is responsible for the distribution of the different coloured pigments during development and these are affected by the morphogenesis process described above, creating the patterns and colours on the organism’s coat. These dictate whether the pattern appears to be uniform or more random. In instances where the pattern changes from childhood to adulthood, such as in the case of the zebra shark, the pigment pattern develops in the living creature.

The pattern differences can be seen across animals and species. Even within a species there can be wild variations. In cats, for example, coats range from stripes, to solid colours to blotches. Researchers have identified the specific gene responsible for the colourations and have demonstrated how the mutations of this gene can cause the pattern to change from splotches to stripes and vice versa. One mutation of the gene is also responsible for supressing pattern formation, which explains why some cats are just one colour. This explains how the differences have developed through the evolution of the species.

This is all very well, but what would be the purpose of this development of spots versus stripes and vice versa? The obvious answer that explains the variations in some creatures is that they have evolved to look like and therefore blend in to their environment, making them invisible to predators; or that they have evolved a pattern that resembles the poisonous markings of another creature, allowing them to be carefully avoided despite their benign nature. In the case of the domestic cat markings, it is thought that the mutation of the genes responsible for causing the pattern variations has actually happened in order for the cat to develop immunity and that their markings have simply changed as a side effect of this process.

Modern science continues to look into the mystery of spots versus stripes, gradually coming closer to a conclusive answer for why the leopard has its spots. Next time you visit the zebra shark in the aquarium or the animals at London Zoo, don’t take it for granted that their coats look different – marvel at the intricate differences and consider how and why they have formed over many years.

Rita Rova has a keen interest in the study of animals and writes for LoveMyVouchers.co.uk; the UK voucher code site that lists the current offers for visiting London Zoo, the Sea Life Centre and many more animal attractions at a discount.

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