Stepping out of the dusty truck, I inhale a familiar scent. Argentina. Cool air carries a mix of damp earth and burning branches from the aged vineyards across the valley. The scent of desert plants nearby mingle with the sweet, far-off smoke, infusing the air with the essences of creosote, sage, and saltbush stored in the sandy soils under my feet. The silent valley hums with a deep history of a changing landscape, tales of orogeny and erosion witnessed by the resident organisms, recorded in their evolution.
Before me, amidst a sea of low shrubs, lies the salty white hardpan of a dried lakebed – a salar. Snows are still visible in the Andean mountains to the west, balancing on the edge of spring and the blistering summer to come. To the east, the isolated peak of Cerro Nevado emerges out of the desert. The horizon stretches onwards to the south, flat and unbroken, hinting at the distant wind-torn Patagonian steppe and the Fuegian reaches of South America – el fin del mundo.
A buzzard flaps its wings overhead. We are here – the site. At this place we seek to observe a miracle.
I have been charged with researching a rare mammal with a duplicated genome and extraordinary adaptations for desert life. My goal is to capture just one red vizcacha rat – Tympanoctomys barrerae – and return to Canada with frozen samples of the tissue for genomic study.
Recent studies indicate that vizcacha rats are tetraploid, meaning that their cell nuclei have four copies of each chromosome, rather than the usual two copies found in all other mammals. Diploid mammals (including humans) suffer disease or infertility with even a slight alteration from the standard double set of chromosomes. The mystery of how vizcacha rats survive and reproduce with tetraploid genomes—and whether it somehow aids their specialized desert lifestyle—is the motivating force of my journey.
I am with two collaborators – ecologists from the Aridlands Institute in Mendoza – who have graciously agreed to organize permits, vehicles, and supplies for this trip. We are in the Monte Desert of Mendoza Province, western Argentina, about 80 km southwest from the sleepy, tree-lined streets of San Rafael, and have already stopped twice this afternoon to look for signs of vizcacha rat activity – burrows plus fresh scat or urine.
It is not until this stop, our third one, that we finally glimpse these beautiful desert rodents.
From the truck, I grab my notebook and camera and set out perpendicular to the dirt road, traversing between mounds of low shrubs and sandy soil. I am in search of active burrows beneath the saltbush shrubs – called zampa by the locals – where vizcacha rats make their underground homes.
Stripping off the salty outer coating of the zampa leaves, vizcacha rats eat the juicy interior flesh as their main food source. Amazingly, they accomplish this feat with specialized bristles on the roof of their mouth – unique entirely to vizcacha rats – that they vibrate against their lower front teeth. The high salt content of zampa makes its consumption impossible for most organisms in the water-sparse desert, where maintaining a bodily balance of salt and water is especially critical. Complementary to these bristles, vizcacha rats also have highly efficient kidneys that conserve water by concentrating salt in their urine.
Standing near a bend in the salar, elevated about five meters from the hardpan, I imagine an earlier, wetter time. A time when the lake would have lapped at the sandy shore, shaping the landscape in cycles of waxing and waning water levels. The time-span of geologic change is normally an abstraction to me. But in this moment, the generations of transforming scenery are tangible. I see how the best-suited variants for each new environment are preserved and reproduced. I see the process of natural selection. Every living organism is at once a passing witness, participant in, and embodiment of this process; the miracle of adaptation and evolution is one of Nature’s tales of awe.
I bend down to pick a few zampa leaves, pressing one against my tongue to taste the visible salt crystals. Doing so makes me thirsty. I notice that my collaborators are walking back to the truck – it must be time to check a different site.
Turning around to join them, I halt mid-step. I am caught by something subtle. I crouch to peer down a half-moon opening, barely visible beneath a stunted, gnarly shrub. There are no cobwebs, and on the other side, there is a pile of neatly cleaned zampa leaves. I quickly count a dozen openings around the mound, apparently joined in a single burrow complex.
Jumping up, I shout to the truck,
“Guys, guys, this is it! We found them!!”
My colleagues and I identify similar burrow complexes around the entire salar. Incredibly, we realize, our preconceptions of what should be had been blinding us to what was.
At nightfall, we set up 40 live-traps on the mound and the surrounding area.
Returning the next morning, I meet a vizcacha rat for the first time.
There are three males in the wire live-traps, each found at a different mound.
I remove the first animal and place him in my hand. It is apparent the cool night has slowed his metabolism. I warm the three animals in the sun and take ear clips for later analysis. I release two of them back to their burrows.
The third animal we keep. Later, we will euthanize him and flash-freeze six organ types on liquid nitrogen.
In the tradition of respect for all living things, we pledge to protect and steward the body and tissue of our vizcacha rat for the most extensive possible study. The skin and skeleton will be preserved as museum specimens and made available for scientific study. From each tissue, we will extract RNA and generate more than 12 gigabytes of genomic data – information on the number and function of gene copies will be key to understanding how genome duplication works in mammals. Human chromosomal duplications are surprisingly common but poorly understood, leading either to miscarriage or developmental disorders such as Down Syndrome. How the vizcacha rat maintains a quadruple set of each chromosome is a story yet to be told – but one sure to contain insights relevant for human health.
Today, on this spring morning in Argentina, we have observed the miracle of one of Nature’s most creative and enduring solutions to life. This small, delicately furred mammal seems impossibly adapted to the unforgiving desert environment around the salar, be it the result of having a double genome or another reason we are yet to find out. Meeting the red vizcacha rat reinforces my resolve about what is possible for science to discover – an endeavor limited only by our imagination to ask new questions, and determination to seek out their answers.
Soundtrack by Small Colin. Photos by Nathan S. Upham and F. Cuevas.