If you know anything about lizards, it’s probably that they can lose their tails. Some lizards eject their tails even when faced with the slightest danger. Others consider their tails a little more precious, but will let them go if a predator happens to grab hold of them. Once detached, these tails continue to twitch and wriggle, and the lizard hopes that this movement will distract the predator, allowing the now tailless lizard to make its escape.
But in the last month, as I’ve searched for lizards to observe and measure, I’ve been distracted not by wriggling tail remnants but by the intact tails of skinks. My current research focuses on brown anole lizards, and while these animals’ behaviours are fascinating, I’m the first to admit that they aren’t the most visually striking creatures. Sure, the males have beautiful red-and-yellow throat-fans, and the females are sometimes patterned with stripes and diamond-shapes, but they’re solidly built and coloured a respectable and unexciting brown. So as I search among brown leaves and on brown tree trunks for these brown lizards, I can’t help but be distracted by flashes of brilliant, electric blue as the skinks slither past.
In a world where “don’t get eaten today” tops most animals’ to-do lists, such obvious conspicuousness demands explanation. The usual causes of crazy colouration simply don’t apply to skinks. These blue tails are found only in young skinks that don’t yet need to bother about attracting mates with flashy colours. Also, skinks aren’t poisonous or venomous, so the colour can’t function to warn away potential predators. In fact, some biologists have proposed exactly the opposite — that these colourful tails attract the attention of predators.
For this to make sense, these young skinks must live in an especially dangerous world, in which being attacked by a predator is practically inevitable. Their tails would then allow skinks to make the best of a bad situation. After all, if you’re almost certainly going to find yourself in the talons or jaws of some larger, stronger beast, wouldn’t it be best if the part of you they grabbed was the one part you could readily get rid of? Having an electric blue tail now becomes an advantage, because it entices predators into attacking something expendable instead of something important. A tailless lizard is still alive and can still reproduce, and from the perspective of natural selection, that’s all that matters.
The loss of lizards’ tails occurs on small time scales — a lizard may have a tail today and lose it tomorrow, but its offspring will almost certainly be born with a tail. Over much longer periods of time, however, lizards are familiar with loss of another sort — the gradual loss of fingers and toes, of arms and legs. Lizards have lost digits and limbs more than 25 times, including over 10 evolutionary transitions to limblessness in different species of skinks and a single transition that led to the evolution of 3,000 species of snakes (which makes snakes a type of lizard). Though skinks are not very closely related to snakes, their propensity to evolve into a snake-like appearance lends credence to the name they are often called in Hindi: saanp ki mausi (snake’s aunt).
But what’s really remarkable about these shifts to limblessness in lizards is just how common they are. They’ve occurred in every continent — there are legless skinks in India and Africa and Europe, legless geckos in Australia, and snakes everywhere. These sinuous reptiles initially evolved to fill one of two ecological roles — either burrowing into the soil or swimming through the grass. Today, however, the most diverse group of legless reptiles, namely snakes, include ocean-dwellers, tree-climbers, and species that glide through the forest. For a group defined by absence, the limbless reptiles haven’t been held back at all.
That we’ve seen so many shifts to limblessness, in different habitats and in different types of lizards, indicates that there’s room for soil-burrowing or grass-swimming reptiles in all sorts of environments. I was reminded of this in the most un-scenic of locations — a parking lot. A colleague saw a slithering creature out of the corner of his eye, and tried to convince me it was something interesting. Given our location, I refused to believe that it was anything other than the commonest of snakes. But he proceeded to catch the animal in question, and I couldn’t have been more wrong. It was a glass lizard — limbless and superficially serpentine, but not too common and definitely not a snake. As I stood among the cars with this delicate animal sliding through my fingers, I hoped that it would not shed its beautiful tail and marvelled at how this gorgeous creature had made this unseemly parking lot its home. It convinced me that neither tails nor limbs have been necessary in the spread of lizards across the planet.
(Ambika Kamath studies organismic and evolutionary biology at Harvard University)