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Colour blind

Question: Chameleons can change colour according to their surroundings. Can a blind chameleon do the same?

Answer: Contrary to popular belief, chameleons do not usually adjust their colour specifically to blend into their surroundings. Most colour changes are thought to be involved in identification of species types and in social displays.

Chameleons are quite difficult to detect in the wild under any circumstances. This, coupled with the fact that they can change colour, has probably led to the myth that chameleons can change colour to match their surroundings.

The normal colour of many chameleons is a cryptic green-brown. The long periods they spend without moving make them difficult to see—except at night, when they become very pale. A further trick is the chameleon’s walk, which mimics leaves moving in the wind. They move very slowly and each time a foot is lifted off the branch their body sways gently as if rocked by air currents.

Blind chameleons could still change colour as long as their mechanisms for colour change remained intact. But they would not be able to see their surroundings, and so would be unable to adjust their own colour to match them. Any colour changes would most likely correspond to stress coloration as the animal discovered it could not feed.

Stuart Humphries

Department of Environmental and Evolutionary Biology

University of Glasgow

Little suckers

Question: Snails regularly seal themselves into their shells. What is the nature of the sealant, and how do they remove what seems to be a very tough adhesive from the point of contact between the shell and the surface to which it is stuck?

Answer: The snail seals itself into its shell with a mucus similar to the one it leaves in trails when moving around.

To unseal itself it simply produces fresh mucus. A similar effect is seen when using a fresh coat of nail varnish to remove an old coat.

Anne-Marie Chatterton

Shoreham, West Sussex

Dirty old bugs

Question: Do bacteria age? What is the longest-lived single bacterium?

Answer: I doubt if any bacteria have ever died of old age. If a bacterium has enough nutrients to live, it will probably divide into two daughter cells. If not, it will probably form a spore casing that can be revived later on, as in the case of Bacillus or Clostridium.

Bacteria reproduce by binary fission, meaning one cell divides into two. Would you consider both of the cells new? If so, you could say that a bacterium can live forever by dividing itself into infinity.

Fred Asher

by e-mail, no address supplied

Answer: Most bacteria reproduce by binary fission and are therefore potentially immortal. This conundrum was first applied to metazoan organisms in a 1938 essay by Julian Huxley—nematode worms, using the same methods, delivered the elixir vitae.

Nick Wells

Greenford, Middlesex