by Matthew Cobb
Hello everyone, Jerry has kindly (or foolishly) handed over the reins of the WEIT blog to me for the next 10 days or so. See if you can spot the difference!
Some of the most spectacular signs of evolutionary adaptation are the many examples of camouflage shown by animals. Although many examples of camouflage are shown by prey animals seeking to avoid being eaten, predators also use camouflage to avoid detection. My good friend Professor Innes Cuthill of Bristol University, UK, studies animal camouflage, and has just posted this excellent audio slideshow on the BBC website.
Innes describes various cases of how camouflage works in different animal species, and there are some great pictures to go with it. Sometimes, changing color is not actually to do with camouflage – this is the case in chameleons, and also in octopuses and squid, which can use rapidly changing patterns of skin color to communicate in ways we do not fully understand. And by ‘ways’ I mean both what they are communicating and how they change their color so quickly.
One of the most spectacular examples of cryptic camouflage can be seen in the octopus, in this video:
This is taken (without credit!) from a fantastic five-minute talk on underwater animals by David Gallo at Ted.com, which you can find here and which includes some great interactions between squid at around 2m 40s and some cuttlefish showing fantastic rapidly changing color patterns.
One example of camouflage given by Innes Cuthill is the zebra, which he suggests may have stripes because it disrupts their outline, making it more difficult for predators to decide where the zebra begins and ends. This may be true – but in reality we simply do not know what the adaptive advantage is. Indeed, it is possible that the stripes have nothing to do with what is really going on (they may be simply a side-effect of the true advantage), although that seems unlikely. A non-camouflage explanation is that zebra foals are born into a world of stripes, and that the stripes on their parents help to enable them to identify their fellow-zebras, and reinforce their herd identity.
The problem with all these explanations is that they are what the late Stephen Jay Gould called ‘Just So Stories’, after the children’s fables written by the British author Rudyard Kipling (‘How the elephant got his trunk’, and so on). They fit the facts, and they may be true, but they lack the decisive support that science alone can provide: experimental evidence.
In discussing this with Jerry last week, he pointed out that a simple test of the ‘disruption’ hypothesis to explain the zebra’s stripes would be to paint some all black or all white, and see what happens to the predation rate. I suspect that would not be possible, either ethically or practically, but some kind of experiments on zebras, lions, or both, will be required before we can be really sure why zebras have stripes. Post your explanations – and above all, think of a doable experiment that could test your hypothesis!