Why the leopard got its spots
20 October 2010
Why do leopards have rosette shaped markings but tigers have stripes? Rudyard Kipling suggested that it was because the leopard moved to an environment "full of trees and bushes and stripy, speckly, patchy-blatchy shadows" but is there any truth in this just-so story?
A cheetah in the grass.
A BBSRC-funded PhD student at the University of Bristol has been studying the mathematics of animal camouflage. Will Allen is interested in factors that drive the evolution of patterned markings in animals such as leopards, cheetahs and tigers. He has used mathematics to examine pattern development in a number of species of wild cat that live in a variety of environments.
This research helps us to understand how such animals are able to fool the visual systems of humans and other animals and so avoid being noticed when they are hunting or being hunted. Better knowledge of how patterns are viewed by human or animal eyes can, for example, be applied to designing object recognition models in computer vision.
Mr Allen and his colleagues captured detailed differences in the visual appearance of 35 species of wild cats by linking them to a mathematical model of pattern development.
They found that cats living in dense habitats, in the trees, and active at low light levels, are the most likely to be patterned, especially with particularly irregular or complex patterns. This suggests that detailed aspects of patterning evolve for camouflage. Analysis of the evolutionary history of the patterns shows they can evolve and disappear relatively quickly.
The research also explains why, for example, black leopards are common but black cheetahs unknown. Unlike cheetahs, leopards live in a wide range of habitats and have varied behavioural patterns. Having several environmental niches that different individuals of the species can exploit allows atypical colours and patterns to become stable within a population.
Although a clear link between environment and patterning was established, the study also highlighted some anomalies. For example, cheetahs have evolved or retained spotted patterns despite a strong preference for open habitats, while a number of cats, such as the bay cat and the flat-headed cat, have plain coats despite a preference for closed environments. Why this should be remains unclear.
The study also highlighted just how few species of cats have vertical stripes. Of the 35 species examined, only tigers always had vertically elongated patterns and these patterns were not associated with a grassland habitat, as might be expected. However, tigers seem to be very well camouflaged so this raises the question why vertical stripes are not more common in cats and other mammals.
Will Allen of Bristol's School of Experimental Psychology, who led the research, said: "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 research is published today in Proceedings of the Royal Society B.
Notes to editors
Why the leopard got its spots: relating pattern development to ecology in felids by William L. Allen, Innes C. Cuthill, Nicholas E. Scott-Samuel and Roland Baddeley in Proceedings of the Royal Society B.
For copies of the paper, please contact Daisy Barton, Royal Society press office firstname.lastname@example.org.
BBSRC is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £470M in a wide range of research that makes a significant contribution to the quality of life in the UK and beyond and supports a number of important industrial stakeholders, including the agriculture, food, chemical, healthcare and pharmaceutical sectors.
BBSRC provides institute strategic research grants to the following:
- The Babraham Institute
- Institute for Animal Health
- Institute of Biological, Environmental and Rural Sciences (Aberystwyth University)
- Institute of Food Research
- John Innes Centre
- The Genome Analysis Centre
- The Roslin Institute (University of Edinburgh)
- Rothamsted Research
The Institutes conduct long-term, mission-oriented research using specialist facilities. They have strong interactions with industry, Government departments and other end-users of their research.