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The 'why' of a leopard's spots

Researchers have followed up on Rudyard Kipling's classic tale to investigate why some leopards got their spots — and why others are spotless.

In one of his "Just-So Stories," Kipling suggested that the leopard scrounged up his distinctive rosettes because he had to stalk his prey undetected in a "great forest, 'sclusively full of trees and bushes and stripy, speckly, patchy-blatchy shadows." Biologists think Kipling wasn't far wrong: The leopard-spot camouflage helps the cats move stealthily through the shadowed forest. But why aren't all big cats spotted?

Researchers at the University of Bristol have developed a mathematical model that links the patterning of the leopard and 34 other species of wild cats to their different habitats. A paper about their research is being published in the Proceedings of the Royal Society B.

The model suggests that cats living in the trees within dense habitats, with high activity at low light levels, are the most likely to have complex color patterns in their fur. The cats that spent their time in well-lit and uniform environments, such as plains and grasslands, were more likely to have small spots or plain coats. The analysis supports the view that different patterns of camouflage reflect adaptation to different environments -- and it also suggests that those patterns can change relatively quickly.

The findings would explain why black leopards (also known as black panthers) are common, while black cheetahs don't exist. As explained in a news release about the research, leopards live in a wide range of habitats ... and some of those habitats offer lighting conditions and behavioral patterns that would favor black leopards over spotted cats. Cheetahs, however, live in a more limited range of habitats.

The research does raise a few questions, however: The mathematical model generally associates spots with closed environment. But cheetahs are spotted even though they favor open environments, and the bay cat and the flat-headed cat have plain coats despite their preference for closed environments. Why doesn't the model hold true in those cases? (It could be that the cheetah is so fast it doesn't need to rely on camouflage.) And why is the tiger the only species among the 35 studied to have vertically elongated stripes?

One thing's for sure: The researchers aren't stopping with leopards. Like Kipling, they're gearing up to address other questions of coloration. For example, why do zebras have stripes? Some researchers have suggested that the zebra stripes aren't meant to serve as camouflage, but rather as a cooling system or an insect repellent. Mathematical modeling could provide further evidence for or against such hypotheses.

"The method we have developed offers insights into cat patterning at many levels of explanation, and we are now applying it to other groups of animals," the University of Bristol's Will Allen said in the news release.

More about animals and camouflage:

In addition to Allen, the authors of "Why the Leopard Got Its Spots: Relating Pattern Deveopment to Ecology in Felids" include Innes Cuthill, Nicholas Scott-Samuel and Roland Baddeley.

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