It’s well-known that certain types of microbes can survive extreme environmental conditions. It turns out that some animals can, too. In their current paper in the Journal of Experimental Biology, Philipp Comanns and colleagues from Aachen University in Germany describe some of the amazing techniques for adapting to extreme dryness observed in the Thorny Devil or Moloch horridus.
The scientists researched in detail how the lizard, which lives in the deserts of Western Australia, obtains life-sustaining water from its environment. The Thorny Devil has hygroscopic grooves between its spines, which it uses to take up water from morning dew or damp sand. Some desert microbes also use hygroscopy as a means to obtain liquid water with the help of salts that absorb water vapor from the atmosphere (the reason salts can become wet in humid air). But the evolutionary trait used by these lizards is far more ingenious. The tiny grooves between overlapping scales create, in essence, a network of drinking straws. Thus, the entire skin can be used for taking up water, which is moved through capillary forces toward the mouth. Once it gets there, the Moloch rhythmically opens and closes its mouth to ingest the water, while otherwise standing still. So well-adapted is the lizard to its dry environment that this is the only way it can take in water—it can’t drink from a puddle directly.
Thus, the alien-appearing Thorny Devil may teach us about possible adaptation techniques on desert planets, which may make up a significant fraction of all the planets discovered outside our Solar System (the count stands currently at about 3,400, with another 5,000 awaiting confirmation). Many of these exoplanets may have lacked water from the start, while others may have lost their water early in their history. The total number of desert planets may therefore be rather large, with a small fraction of those possibly hosting more complex life.
Mars might serve as an analog for these kinds of worlds. Today, Mars is so extremely dry that we would not expect any complex life on or near its surface, although microbial life may very well be an option. But if the Red Planet had been larger to start with (about Earth-size), it might have retained its protective geomagnetic field, as well as a thicker atmosphere and more water—and who knows, perhaps creatures as odd as Moloch horridus!