The scorching temperatures and vast expanse of the Sahara Desert make for an inhospitable environment. Covering approximately 3.6 million square miles and with daytime temperatures well over 40 degrees Celsius, it is the largest and hottest desert in the world. It is alsoitalic text one of the most sparsely populated—with a mere 2.5 million people calling the desert home. Despite these extreme conditions making it practically uninhabitable to humans, the Sahara is far from barren, hosting a diverse array of unique flora and fauna, including desert-adapted species of reptiles, mammals, insects, and drought-resistant plants. Nonetheless, life in this unforgiving landscape comes with its challenges. As hyper-arid regions like the Sahara are experiencing increasing dryness and warmth, both animal and human habitants must face the daunting task of adaptation. How do they endure and thrive amidst these shifting sands and rising temperatures?

To answer these questions, desert scientists seek to understand adaptive evolution, a biological process wherein an organism undergoes genetic changes over generations, leading to the emergence of traits that improve their survival and reproductive success. Plants and animals that can survive in harsh climes present as unique systems to study the intricate interplay between genetic changes and survival strategies.

For her PhD work, Dr. Joana Laranjeira Rocha, a postdoctoral research scholar in the Department of Integrative Biology, chose to study adaptive evolution in different charismatic species of fox that call the Sahara home. Supervised by Dr. Rasmus Nielsen at UC Berkeley and Dr. Raquel Godinho at the University of Porto in Portugal, this transcontinental collaboration brought together the expertise of two distinguished institutions in the field of population genetics and uniquely positioned Rocha to unravel the mysteries of these resilient desert-dwelling species.

A diversity of adaptations among desert foxes offers a captivating view into the versatility of evolutionary processes. From the iconic fennec fox with its large ears (perfectly adapted for heat dissipation) to the swift Rueppell’s fox that navigates sand and stony deserts with ease, each Vulpes species of the Sahara has honed specific traits that optimize their chances of survival in the unforgiving desert landscape. By pinpointing specific genes likely under selection and evolutionary routes for adaptation, Rocha’s team was able to better understand the origins, mechanisms, and genetic architecture behind adaptation and evolution in deserts.

“The Vulpes system in itself is a very compelling and outstanding evolutionary case study,” explains Rocha. “It allows us to address adaptation to different environments overall, and also questions of how, within a genus, species can diversify so fast and adapt repeatedly to similar if not the very same extreme environments.”

Rocha’s research on desert foxes goes beyond the realm of scientific curiosity. As the Sahara and other desert regions are facing the impact of climate change and human activities, understanding how these adaptable creatures respond is becoming increasingly relevant for conservation efforts. “This research could ultimately draw attention to biodiversity and communities threatened by increasing desertification,” Rocha notes.

To answer fundamental scientific questions about extreme-environment adaptation and evolution in desert foxes, Rocha and her PhD advisors knew they would have to assemble an expert team of field biologists and desert ecologists. Capturing a fox in this vast and harsh landscape would be far from easy.

“I was surrounded by a team of people and never alone,” Rocha emphasizes. She would count on the expertise of researchers from the University of Porto: Monia Nakamura, a field biologist, and Dr. Nuno Santos, a wildlife veterinarian. Both Nakamura and Santos were new to the North-African desert, but were well-acquainted with the challenges and art of capturing and sampling wolves in Northwestern Iberia. To them, sampling foxes in the Sahara was a unique opportunity to put their skills to the test and continue developing their craft. To navigate the unfamiliar desert landscape, the team utilized the wisdom and knowledge of other desert ecologists, including Dr. Jose Carlos Brito at the University of Porto and Professor Abdeljebbar Qninba at the University of Rabat in Morocco. Most importantly, the team relied on local Saharawi guides Mohamed Lamine Samlali and Bhaya Habib to conduct field work under optimized safety conditions.

In the world of scientific exploration, it takes a collective effort of dedicated experts and collaboration among numerous institutions to undertake research of this magnitude. Through combined expertise and tireless commitment, these researchers have overcome immense challenges and ventured into the heart of the Sahara to study these remarkable desert-adapted animals. Their efforts have propelled us one significant step closer to unraveling the mysteries of how these creatures thrive in scorching climates, shedding new light on the intricacies of adaptation evolution.

Surviving the Sahara: Tales of trial and triumph

Rocha’s study centers on four distinct fox species with populations within and around North Africa. First is Rueppell's fox, renowned for its adaptability and sandy fur, and which thrives in arid environments. Next is the globally recognized red fox, distinguished by its red or orange fur and bushy tail; a particular focus on its North-African population offers intriguing insights into their more recent desert survival strategies. Third is the Fennec fox, notoriously known for its large ears that aid heat dissipation and ability to survive without water; they predominantly inhabit the heart of the Sahara Desert and other arid regions. Finally, there is the lesser-known Pale fox, aptly named for their pale coats, which has populations spanning into the Sahel, a transition region sandwiched to the north by the dry Sahara and to the south by humid savannahs.

Rocha’s team gathered biological samples from various sources, including foxes captured in the wild, those held in captivity, and road-killed animals collected across regions in North Africa, the Middle East, and Europe. In North Africa, fox captures occurred in two distinct regions in Morocco: the Draa Valley in the Guelmim-Es Semara region and the Western Sahara in the Dakhla-Oued Ed-Dahab region. Additionally, researchers sampled captive foxes from public and private zoos in Morocco and biological parks in Portugal. This comprehensive collection of biological samples from diverse sources and geographic locations allowed for a thorough investigation into the genomics and physiology of Vulpes foxes.

The field work required the team to venture into the vast and unforgiving Sahara Desert, demanding not only courage but also an exceptional understanding of the environment. For Dr. Jose Carlos Brito, the Sahara Desert is a familiar landscape. For decades, he has ventured into this sea of sand, having spent long periods of time in a landscape where even the hardiest of humans struggle to survive to study animals that call the Sahara home.

“It’s critical that you set up the conditions for survival of the team. And this means water, fuel, and food. On many occasions, we spend 15 days, for instance, without access to any of these resources. So, this requires taking jerrycans and [getting] the supplies in villages before heading to these remote destinations,” Brito explains. These calculations are a matter of life and death—experience is what counts.

Over the course of these decade-long scientific expeditions, Brito collected dozens of road-killed fox samples that would then become an integral part of Rocha’s work. Rocha’s maiden field experience was a trip to the Sahara. It was a trial by sand—the first expedition only yielded one fox sample, a frustrating and disheartening experience. Foxes are elusive creatures and their nocturnal schedules meant that her team had to work through the night to collect samples.

"The expeditions were typically one month at a time," Rocha explains. "We began by setting camera traps strategically, learning from previous attempts. It was about finding the right balance between knowledge of the foxes' habits and being at the right place at the right time."

The team’s tenacity and persistence led to a pivotal moment during their second expedition when camera traps captured the foxes in action. "It was amazing to see that the animals were there," Rocha recalls. Subsequent nights became a blur of vigilance, with alarms from non-lethal traps alerting the team to rush for emergency-style captures and sampling. Sleep became a rare commodity, as they worked tirelessly through the night, ensuring the integrity of collected samples.

But as much as the team understands the power of the desert, they also dwell on its beauty.

“It is impossible to be indifferent to a desert,” says Brito. “In my case, I love it. You have this wide-open space, where the horizon has no limits. You can see the stars at night. It’s a unique and special environment to work in.”

Genes on the evolutionary fast track

It’s hard to understand when and why foxes first came to the desert without some context on how their genetic cousins operate outside of these environments. Comparative studies of closely related species living in diverse habitats can offer valuable insights into the evolutionary processes that led to the emergence of fox species with desert adaptations. By examining how these similar species behave and survive in different ecosystems, researchers can unravel the genetic and physiological changes that facilitated the Saharan fox species’ transition to thriving within the challenging desert environment.

Delving deeper into this evolutionary narrative, Rocha’s team employed advanced computational models to trace the demographic histories of both Rueppell’s fox and the red fox. This is a bit like how services like 23andMe trace ancestry; they analyzed specific genetic markers in DNA and compared them to a reference database of global populations to estimate geographical origins and genetic heritage. The team’s analysis unveils an intriguing evolutionary split, demonstrating that the Rueppell’s fox took a distinct evolutionary path that landed them in Northern Africa approximately 576,000 years ago.

In stark contrast, the red fox embarked on a journey starting from Eurasia and spread its presence to diverse regions worldwide, with a branch ultimately making its way to North Africa more recently, about 78,000 years ago. The saga of the North African red fox is tightly interwoven with the fluctuating paleoclimatic history of the Sahara known as the “Green Sahara,” a transient period when abundant precipitation and favorable conditions lead to verdant grasslands covering the Sahara. The historical context underscores the emergence of all North African fox species as an extraordinary case—a natural experiment unfolding over different timescales, offering a vivid illustration of how these foxes adapt to changing conditions within the desert.

To comprehensively understand desert adaptation, the researchers compared their findings to foxes in temperate and Arctic regions. By comparing their genetic makeup, behaviors, and ecological interactions to those of their desert-dwelling counterparts, the team was able to unearth valuable insights into potential adaptations essential for survival in vastly distinct climates. Genomic analysis revealed a distinct selection of genes linked to critical functions such as renal water balance, pigmentation, and response to ultraviolet radiation, all pivotal for navigating the demanding conditions of the extreme desert environment.

One example, renal water balance, which is the ability to effectively manage water levels in the body through the kidneys, is a crucial adaptation for survival in desert environments. In arid desert conditions, water is a scarce and precious resource. Animals living in these regions must efficiently regulate and conserve water to withstand prolonged periods without it. Renal water balance allows animals to reabsorb and retain water within their bodies. Animals with effective renal water balance can concentrate their urine, extracting the maximum amount of water from the waste products before excretion. This is essential for preventing dehydration, maintaining proper bodily functions, and ensuring overall health. Rocha further identified the WFS1 gene in the Rueppell's fox, which is associated with urine-concentrating ability during water deprivation in mice. WFS1 is thought to influence the secretion of vasopressin, a hormone critical for water reabsorption at the kidneys. While the precise mechanism between the two is still being fully elucidated, it is plausible that WFS1 plays a role in the regulation of water balance in foxes. This may explain the higher urine-concentrating ability observed in Rueppell's fox, enabling it to retain water more effectively. Similarly, the KIRREL1 gene, known to influence kidney function, was found in the fennec fox and likely contributes to its superior urine-concentrating ability compared to the red fox. The ability to optimize renal water balance allows for desert-adapted animals to survive with lower water intake, making them well-suited to the challenges of limited water sources and high temperatures in the desert. This adaptation is a key component of their ability to thrive and persist in such extreme and water-scarce environments.

Rocha also included physiological analyses into her study, which require examining the functions and activities of biological systems, tissues, and cells within an organism, thus integrating the study of the foxes’ biological responses alongside genetic analysis. Such multidimensional approaches would help paint a more comprehensive picture of how these animals survive and adapt to their environment. The findings were intriguing, revealing that both the Rueppell's fox and the fennec fox showed lower levels of the thyroid hormone thyroxine compared to the red fox. Thyroxine plays a role in regulating metabolism and water balance and lower thyroxine levels reflect lower metabolism and lower urinary water loss, both of which are advantageous qualities for living in the desert. Honed over generations, this underscores the role of evolution in helping species thrive in the demanding and ever-changing environments of desert ecosystems.

Unraveling the tale of The Little Prince’s fox

When Rocha was growing up in Portugal, one of her favorite stories was The Little Prince by Antoine de Saint-Exupery. In this novella, a young prince travels from planet to planet, meeting various inhabitants, including a wise and insightful fox with whom he develops a strong bond.

“It’s a story about friendship and connection, and how people that pass by each other, give a little piece of each other to the other person,” emphasizes Rocha. “The story of the relationship of The Little Prince and the fox illustrates the kind of scientist that I want to be. I want to have this kind of relationship not just with the foxes of the desert I was trying to capture, but with the foxes of my life—students, collaborators, colleagues, and advisors.”

One of Dr. Rocha’s “human foxes” on this collaboration was none other than her sister, Margarida Laranjeira Rocha, a 2D animator, who drew the illustrations for her paper. “Illustration is great when it comes to science,” explains Margarida Rocha. “Science is something that is developed by the human mind, and illustration is done by the human hand—it all comes together in a ‘man thinks, man creates, man discovers’ kind of way.”

The harmonious fusion of science and art in this sister-sister duo brought vibrancy to the visual representations of the foxes’ adaptations. Beyond the aesthetic allure, the creative partnership holds significance, highlighting the interplay between a scientific lens and a creative one. “It’s magical and interesting—we each have different relationships with the world that surrounds us, and that is really great,” Margarida L. Rocha elaborates.

This unique collaboration not only enriches the visual representation of the foxes' adaptations but also stands as a testament to the versatility of the human mind, where the worlds of art and science can seamlessly converge to enhance our understanding of the natural world. More than that, this collaboration resonates with the spirit of the Sahara, where resilience, adaptation, and evolution are etched into the very fabric of life. Just as the Little Prince and fox forged a bond that transcended their differences, this collaboration bridges the realms of art and science, shedding light on the world of desert adaptations and the intricate tapestry of evolution itself.

Surviving the crucible: Life finds a way

The Sahara, with its boundless horizons, might appear inhospitable to life, but a mesmerizing world of survival strategies and genetic marvels lies beneath its surface and within its intricate ecosystem. Here, animals and humans alike are locked in an unending battle against an environment that ceaselessly tests their mettle. The most improbable of protagonists navigate the harshest of environments. And through their own scientific adventures, researchers have unveiled the secrets of nature’s tenacity in the face of adversity.

Once misconceived as barren, the Sahara pulsates with an astonishing diversity of life. Amidst the harshest conditions, its inhabitants, including the resilient desert foxes, display remarkable prosperity—offering profound lessons in adaptation. Their ability to endure and even thrive in this severe environment provides us with inspiration and a blueprint for our own journey on an increasingly warming planet. Meanwhile, other species of flora and fauna can teach us about water management, climate-resilient agriculture, responsible land use, and habitat restoration. As the world grapples with the consequences of climate change, the Sahara's adaptable inhabitants serve as harbingers of hope.