BY ALPER ÖZKAN (MSN/PhD)
d_ozkan@ug.bilkent.edu.tr
Life on the Edge
Arctic and Antarctic environments are similar to deserts, in a way: both are mostly inhospitable but have transient periods of habitability that are exploited by a wide range of fast-growing plants and animals, and if you’re really hell-bent on staying year round, both can be tolerated with the right set of adaptations. Temperature modulation is key to survival in both biomes, and Allen’s rule is more important than ever: where desert animals tend toward large ears
and small bodies to easily dissipate heat, cold-adapted beasts are bulky and have small extremities that conserve the same (compare, say, an Arctic fox to a fennec). But there are some animals that have taken these rules of thumb and cranked them up to eleven, sacrificing their ability to live anywhere else and becoming the rightful kings of the tundra and the desert. Let’s take a look at some.
A desert is no place for a crustacean to be—even terrestrial crabs and woodlice are dependent on atmospheric moisture to keep their lungs functional, which restricts their distribution to shores and other humid environments. The woodlouse Hemilepistus reaumuri, however, is perfectly at home on the sands, thanks to a combination of physiology and behavior. In addition to the water-retention mechanisms common to desert-dwelling animals, it also walks with a raised gait to minimize its contact with the burning desert (this is also seen in other desert arthropods, which run on stilt-like legs to avoid both the ground and the hot air above it), and digs burrows reaching half a meter in depth to recharge itself on subterranean moisture. These woodlice also care for their young, allowing their vulnerable hatchlings to survive in the unforgiving desert—a similar development of parental care under duress is also found in some intertidal beetles, which actively regulate their burrows to save their offspring from a watery death.
While desert animals must focus heavily on preventing water loss, things are no different for tundra-dwellers: evaporation and freezing both take a heavy toll on precious water reserves. In addition, water expands during freezing and tends to destroy cell membranes in the process, so it is usually best not to freeze at all—organic antifreezes are consequently very common in nature, and due to their tiny size, insects and other invertebrates can readily supercool to very low temperatures (down to -40 °C for mites and other very small arthropods) without freezing. While ideal for living in the cold, these adaptations also have their drawbacks. Icefish, for example, have their blood loaded with antifreeze but almost entirely lack hemoglobin, relying on the enhanced oxygen-carrying capacity of cold water to survive—thereby restricting themselves to colder waters. Worse yet, the glacial annelid Mesenchytraeus is entirely incapable of leaving its frigid home, as it melts under the sun—temperatures above a few degrees Celsius are fatal to it. Snow fleas, cold-adapted flightless scorpionflies, are also unable to tolerate higher temperatures, but come with a twist: one group of snow fleas did, in fact, evolve to live in warmer climates, eventually becoming…fleas.
The interplay of heat and water, however, only reaches its apex in the desert cicadas. These animals begin their noisy chorus during the hottest hours of the day, avoiding their predators by surviving where none dare tread. The secret to their endurance is in their choice of food. As with all homopterans, these insects feed on plant juices, which can be drained and excreted at staggering rates. Equipped with an abundant source of water, the cicada is free to pump it outside its body, where its evaporation will cool the animal. Other insects, rather than taking water from plants, have managed to make their own. There is, for example, a desert beetle that can gather water from the atmosphere through a series of microscopic bumps and channels on its back, and this has become a prime example of the potential of nanotechnology (which was used to replicate the beetle’s wing structure and create a water-harvesting device). But what impresses me more is another, related desert beetle, which has no bumps on its wings and must obtain water by digging ditches that are directly perpendicular to the fog, thus causing it to condense on their edges.
That’s right, there’s a moisture-farming beetle. I await the day one of these things leaves its run-down farm, goes on a galaxy-spanning adventure and fulfills its destiny to bring balance to the Force.e.