NEWSDAY (New York, New York) 11 December 05 Losing it in a tight squeeze (Kathy Wollard)
How and why do lizards detach their tails? asks F. Samuel, of Kerala, India.
When approached by a mugger, some people toss their wallets onto the sidewalk -- and then turn tail and run as fast as they can.
If the wallet is shiny fuchsia with lime-green polka dots, so much the better. A distracted mugger is less likely to give pursuit. And if the wallet is empty? Best of all.
Many lizards have evolved a similar survival skill, but it's the tail that gets tossed. Often, a lizard's tail is its most striking part -- bright blue, neon green, fire-engine red, zebra-striped. The left-behind tail, wriggling colorfully on the ground, often is distracting enough to a predator to allow the lizard a narrow escape.
Tail-dropping is such a useful survival tactic that most lizards (at least 13 of 20 lizard families) can do it. This odd talent is called caudal autotomy (meaning "tail, cutting off of".
But tail self-amputation isn't as traumatic as major surgery. In fact, tail-dropping often is a choice -- albeit an adrenaline-fueled choice, usually made while a lizard is speeding away from something out to eat it.
Scientists say that it's easier for a lizard to drop its tail while on the run, rather than when the tail is gripped by a predator. In most tail-dropping lizards, tail bones are perforated ("tear here". A sharp squeeze of the muscles around the perforation breaks the bone. Muscles and connective tissues separate; the tail falls. Muscular rings neatly close off torn blood vessels. Firing nerves in the severed tail allow it to continue twitching.
Lizards who evolved to drop their tails also have the ability to grow them back. (That is, if they live long enough after their scary experience -- several months to a year.) However, the replacement is far from an exact copy of the tail they were born with. Instead of connected bones -- the vertebrae of the original tail -- the new tail is made of simple cartilage, like a human nose.
Besides being less sturdy, the tail is a cheap copy in other ways, too -- shorter, with muddier colors and smeary (sometimes backward) patterns.
In fact, tail-dropping is a last resort for lizards. Some use their tails as a counterbalance when running on their hind legs, or as an extra "hand" to climb trees. Some tails secrete an adhesive, to keep lizards from falling off slick surfaces. With no tail, a lizard has less skin surface to absorb sunlight and stay warm. And lizards that swim find that, sans tail, they can't.
Like a camel's hump, tails are a storage depot for fat and protein, a source of calories when food is scarce. And the period of healing and tail regrowth saps extra energy, forcing functions like growth and reproduction to shut down.
To add to the post-traumatic stress, tailless male lizards can't defend their territories as well, and they find their status has dropped along with their tails. And a lizard without a tail -- or with a not-so-nice copy -- apparently isn't as attractive to the opposite sex.
On the bright side, it's better than being eaten.
Losing it in a tight squeeze