How do animals adapt to live in the Sahara?

The Takeaway: Living in the Sahara Desert is tough for animals of all kinds. But a combination of genetic changes and natural selection have meant that some have adapted and even thrived.

In the summer of 1815, the Connecticut-based U.S. brig Commerce sailed out of Gibraltar on its way to the Canary Islands and eventually the West Indies. Drifting for days in dense fog, the boat sailed too close to land and was pummeled by waves onto the rocky shore of Cape Bojador, which is on the central coast of what is today the disputed territory of Western Sahara. Broken apart on rocks, the stunned crew waded on to shore only to find an unwanted welcome party—wandering, hostile Bedouins.

To their surprise and horror, the crew of the Commerce was captured by the Bedouins and immediately sold into slavery, an act which began a months-long ordeal where the men wandered the Sahara with their owners, charged with feeding camels and gathering sticks for firewood, rarely fed, and only occasionally given camel milk to drink. The captain, James Riley, later wrote a vivid account of the ordeal, describing weeks of forced marching across desert sands and rocky plains, sleeping on the open ground at night, going days without seeing so much as a twig or a mosquito—except one day, when they came across the tracks and dung of wild animals, heard howling in the inky blackness of night, and then gained a furtive glimpse of a solitary four-legged animal loping across the sands.

What animal was this? And how could it survive in such a hostile environment? In his journal, which became a best seller, Riley identified the animal as a leopard, though scholars today suggest it was more likely a wildcat, cheetah, or a fox.

Today, more than two centuries later, scholars are learning more about these tenacious desert dwellers, and the sorts of genetic adaptations they have acquired to allow them to live in such extreme terrain.

How can some animals thrive in the Sahara?

Genome sequencing has revealed how some animals thrive in places where most other living things can’t. Writing in Nature Ecology & Evolution, an international team of researchers sequenced the genomes of several species of foxes to understand just how they can live in a place that may go a year or more without rain. Sequencing was done on samples from North African, Eurasian red, North African Rueppell’s, fennec, and pale foxes, all of which lived in the Sahara at one time or another.

While “the Sahara” has been in existence for at least 2.6 million years, its boundaries shift, and a more recent phenomenon, desertification, has further challenged desert dwellers as they seek to find a niche habitat to thrive in. Part of the ability of these animals to live in this extreme environment is due to the genetic adaptations they possess.

Researchers in Nature found that Rueppell's fox diverged from the red fox about 576,000 years ago. The Rueppell's fox adapted to live along the edge of the Sahara while the red fox drifted east into Eurasia and then, about 78,000 years ago, back to North Africa. Additionally, the team found that the Rueppell's fox genome mixed with red foxes in North Africa.

So how do these animals manage to survive in a region that might see a rain shower or two each year? Genetic signatures of the Rueppell’s fox and fennec fox showed specific genes involved in water homeostasis—homeostasis being the way that animals balance the water they take in with what they perspire, poop, pee, breathe out, or lose through their skin; that analysis found that these two animals are better at retaining water when dehydrated.

"We propose that genetic variation shared among core desert species is an important component of recent or ongoing adaptation to rapidly changing climates in foxes living at the edge of deserts," the researchers write. "Our findings may thus help address questions concerning the persistence and adaptive capacity of biodiversity currently challenged by desertification."

Genetic adaptations of desert animals

The ability of foxes to balance water intake in dry climates is just one example of genetic adaptations that are present in desert dwellers. Others involve fat metabolism and insulin signaling. These adaptations are further notable since deserts are not static environments—while the trend in the Sahara and along its margins is toward increased desertification, deserts around the world range in age from just a few thousand years old to millions of years old, and some deserts alternate between periods of extreme aridity and periods of increased rainfall and humidity.

“The major mechanisms shared across mammals relate to phenotypes that have been associated with adaptation to starvation and dehydration, as well as water retention at the kidney,” noted one study that summarized recent genomic insights into desert dwellers. These mechanisms include genes that affect:

• Energy expenditures
• Cold and diet thermogenesis
• Fat metabolism
• Adaptive tolerance to heat and cold
• Dehydration and water retention
• Food scarcity and starvation
• Insulin signaling and response
• Adipocytokine signaling

“Taken together, these studies not only show that adaptive changes in fat metabolism, insulin response, and arachidonic acid metabolism may be pivotal for mammalian survival in different deserts of the world, but also that water and food deprivation, perhaps more than temperature, are likely the main drivers of convergent evolution in deserts,” the report said.

Genetic adaptations of Saharan desert dwellers

Animals that live in the Sahara and other deserts have adapted genetically to the dry environments. Some of those include:

• Water conservation tools, such as efficient kidneys that concentrate urine and extract water from food that is eaten
• Thermoregulation adaptations, such the ability to sleep through the hot parts of the day and large ears that help animals shed heat
• Camouflage and coloration patterns that provide protection from predators and help them blend in with their environments
• Specialized diets, including digestive systems that can more efficiently extract water from plants that are eaten
• Resistance to dehydration, including cellular and molecular adaptations that prevent damage from dehydration

Novel desert survival tactic: Growing faster by shedding unneeded DNA

Foxes aren’t the only dwellers whose genomes have adapted to allow them to live in deserts. In deserts of North America, the New Mexico spadefoot toad (Spea multiplicata) genome was found to contain a number of unique genetic adaptations. Sequencing the animal’s genome for the first time, a team of American researchers found that these desert dwellers possess rapid growth and development attributes, prolonged dormancy, phenotypic plasticity, and adaptive interspecies hybridization.

In particular, they found, larval development time is positively correlated with genome size.

“The small genome size and rapid development of Sp. multiplicata exemplify this relationship,” researchers wrote. “The genomic factors that contribute to variation in genome size remain an issue of active inquiry. We found that, despite their smaller genome, spadefoots are similar to other sequenced anurans in terms of number and type of genes. Thus, Spea’s smaller genome appears to derive from diminished repetitive and intronic DNA, which is consistent with the prevailing hypothesis that genome size has undergone gradual change—as opposed to abrupt change—throughout much of amphibian evolutionary history.”