What Do We Lose If We Lose Wild Axolotls?
Axolotls could revolutionize medicine, but their wild cousins are critically endangered.
On a crisp November morning a little after dawn, grey mist unspools from the surface of the water of a maze of canals and island farms called Xochimilco. I’m just a dozen miles south of the center of Mexico City, a sprawling mega-metropolis, but right now, that’s easy to forget.
Herons line the trees along the banks of the canals. Mountains fade in at the horizon. This early, it’s cold enough that Alejandra Ramos and I are shivering as our boat hums through waterways. When we arrive at Antonio Mendez-Rosas’s farm, the vegetables still look like they’ve been dipped in sugar crystals.
These canals are the very last wild habitat left for what we’d like to find—a strange salamander called the axolotl, which Ramos, as part of a team from Mexico’s National Autonomous University, is working desperately to save from extinction.
The axolotl is famous and beloved, a celebrity among amphibians. Named after an Aztec god and the inspiration for a Pokemon, it can heal itself better than Wolverine from the X-Men, even regrowing lost limbs. The people of Mexico City recently chose it as their official emoji.
But there aren’t any here today. Mendez-Rosas, the farmer, says that fishermen used to cast a net and catch 40 at a time. Now, standing by the side of a canal and beckoning us closer, he points to the last place he saw an axolotl wriggling in the mud…more than a year ago. Their population density in these wetlands has nosedived from an estimated 2,340 salamanders per square mile in 1998 to less than 14 per square mile in 2014, the year of the last census. No one knows how many are left now.
On its surface, the axolotl’s plight is the same one faced by countless endangered species around the globe. In Xochimilco, as in many other places, humans have pressed heavily against an ecosystem, imperiling plucky, charismatic creatures. Here, our slimy protagonist is beset on all sides. First, its wetlands have shrunk as Mexico City’s population exploded from about 3 million in the 1950s to some 21 million today. Second, some farmers have introduced invasive carp and tilapia, which gobble up axolotl eggs and compete with adults for food. And third, pollution and sewage have reduced the water quality.
But like all good stories, the quest to save the axolotl is more than it seems. Set in crowded Mexico City, it is a microcosm of conservation in the 21 st century. It isn’t a binary choice between pristine wilderness and human despoilment—Xochimilco has been home to island farms like Mendez-Rosas’s for over a thousand years, with axolotls thriving alongside people. And unlike many fragile species, the axolotl won’t go extinct if it’s extirpated from Xochimilco. For well over a century, the salamanders have been raised in laboratories and kept as pets across the globe. They’ll continue to exist as curios and sources of biomedical inspiration.
The future of this salamander will be determined not by which plot of land we chose to preserve, but by how we answer a deeper question: What do we lose if Xochimilco loses its axolotls?
A Colonial Conquest
I first caught the axolotl bug this past summer, when a friend went on a few dates with a grad student who kept some in a genetics lab. Once I started looking, they turned up everywhere. I saw them preserved in jars in the herpetology collection at Harvard University and others alive in a developmental biology lab upstairs. I even met a pet axolotl owned by a toxicologist in Japan.
There’s a good chance that each of these animals can trace their ancestry to just one event, the start of the global axolotl diaspora. In the summer of 1863, while the Union and the Confederacy were busy slugging it out at Vicksburg, France invaded Mexico City to collect on unpaid debts. Hot on their heels, naturalists and biologists followed, as often happened with Enlightenment imperialists.
At the beginning of that century, Napoleon’s troops had dragged the Rosetta stone and other ancient wonders out of Egypt. In conquered Mexico, the French went searching for archeological discoveries to match the Rosetta stone. Perhaps they could find another mystical object with the power to unlock vast recesses of time, to illuminate hidden relationships. They did—only it was biological, not archeological. In 1864, 34 live axolotls were shipped to Paris, and six of those were given to biologist Auguste Duméril. He bred them and shared their progeny with international colleagues. Lab axolotls have been going strong ever since.
Almost immediately, Duméril’s axolotls earned their keep. Axolotls never metamorphose, a curiosity among amphibians and something Duméril likely knew at the time. Instead of losing their gills and crawling onto land like other salamanders, axolotls happily spend their entire lives underwater. They even breed in that form. But in 1865, something even weirder happened. Some of Duméril’s second generation of axolotls spontaneously transformed into air-breathing adults.
It’s possible the Aztecs already knew that axolotls could do this. The concordance is just too perfect: their namesake god Xolotl, twin brother of Quetzalcoatl, had the power to shapeshift. Either way, this hidden extra rung in axolotl development helped early 20 th century scientists discover thyroid hormones, which can reliably induce the change.
Today, it seems fair to ask whether the descendants of Duméril’s six salamanders, having lived past the sesquicentennial of their captivity, are even true axolotls anymore.
Digging in, I found a 2015 paper titled, charmingly, “A Tale of Two Axolotls.” One of the paper’s authors, Randall Voss, runs the Ambystoma Genetic Stock Center, a repository of lab axolotls hosted at University of Kentucky and funded in part by the National Institutes of Health. The Kentucky salamanders are different from wild ones in some key respects, he told me on the phone.
For one, this population is nicer. “It was clearly selected to like human beings,” Voss says. “If you walk into our facility, they’ll just instantly make eye contact, come to the edge of the tank, and start begging for food.” They grow and breed fast, too. But compared with Xochimilco’s axolotls, they are all genetic hybrids. Over time, for reasons that are not totally clear, the lab population of axolotls has been crossbred with other tiger salamanders, the larger taxonomic group to which axolotls belong. That has left many lab specimens with a host of foreign genes, including those that code for a milky white skin, unlike the darker shades of wild axolotls.
The axolotl wasn’t appreciated in modern, developed Mexico until the last few years, Zambrano says, well after development had put it in the crosshairs.
Even the wild axolotl had long been an urban animal, says Luis Zambrano, a biologist at the National Autonomous University in Mexico City and another of the “Two Axolotls” authors. It thrived alongside the Aztecs for centuries. But the axolotl wasn’t appreciated in modern, developed Mexico until the last few years, he says, well after development had put it in the crosshairs.
In 2002, the federal government tasked Zambrano with a simple mission: form a scientific opinion about the state of this species. But first he had to catch some. He set out traps full of minnows, stretched out gill nets—nothing. “It was a nightmare,” he says. “I said I would finish this work and never come back to Xochimilco.” Finally, he went to a local festival and met fishermen who knew how to catch axolotls the old way, with cast nets. If you want to get axolotls, they said, hire us. So he did, eventually finding a long-term fishing partner for his research.
Zambrano did return to Xochimilco, again and again, and in the intervening years, he has witnessed its axolotl population dwindle. Faced with a bleak state of affairs, his team has two plans to save the wild salamander. Plan A, the optimistic one, is to protect some of Xochimilco by preserving old-school, axolotl-friendly farming practices. Plan B is to establish another axolotl habitat—an off-world colony, if you will—in the hopes that Xochimilico will be restored…or as a failsafe if it isn’t.
A Future Like the Past
Even as the species hangs in the balance in Mexico City, the axolotl is still a star on the rise in the research world. After all, this salamander could well spark a revolution in medicine, giving us the power to regenerate tissue, heal any body part, maybe even regrow an entire arm or leg.
In the beginning of February, an international team took a major step toward tapping into that power, with the announcement in the scientific journal Nature that the full axolotl genome has been mapped for the first time. With 32 billon base pairs, it’s the longest genome previously sequenced, ten times longer than ours.
To understand how axolotls might someday transform medicine, I meet Jessica Whited in the lobby of a patient building on the bustling campus of Brigham and Women’s Hospital in Boston. Whited, a researcher in the hospital’s department of orthopedic surgery, whisks me upstairs in a whirlwind of energy. In her office, she pulls an undergraduate biology textbook off the shelf and flips to the index in the back.
“Regeneration,” she says, scanning. “In this entire textbook, there is one page. 768. This is why I wanted to work on it.” There’s another reason, too. Her grandfather had a peripheral artery disease, in which plaque chokes off blood flow in a person’s extremities. Half of amputations come from such diseases these days, Whited says, and the other half from trauma. Her grandfather required a series of amputations: a few toes at first, and then his leg below the knee. He died at 62.
Recently, Whited’s team has investigated what exactly happens when a salamander regrows an amputated limb. After about the fifth amputation, even axolotl tissue eventually gives up and responds like a human amputee. That lets her compare axolotl stumps that can regenerate against those that can’t.
When these stumps didn’t sprout new limbs, it seemed to be because regeneration was blocked, not because it wasn’t sufficiently encouraged. Whited found that the genes in inactive stumps were expressing in overdrive, as if those genes were actively stopping the process. (Until this point, scientists had mostly looked for the opposite—genes that are silent in stumps but turn on when a limb needs to regrow.)
And at least one of these genes that stops axolotl tissue from regenerating is closely related to a gene in mammals that causes scarring. Regrowing a limb, it seems, could be an ancestral response that our own bodies just suppress.
Another bit of dogma has been that the magic of regeneration happens right at the stump. But that’s not true in axolotls, Whited discovered. When they lose a limb, cells in the heart, spinal chord, liver, and perhaps all over the body are called into action and start dividing. This happens in mice, too—if you injure a mouse’s leg, muscle stem cells in the other leg start dividing—and it may happen in humans as well.
“It’s possible that we’re not as bad off, from a medical standpoint, as we thought we were,” Whited says. This body-wide response is like the seed of regeneration. Axolotls form a mass of cells that acts as fertile soil for that seed, while mice and humans don’t. But in the future, maybe, we could engineer a more suitable stump, she says.
As we talk, Whited, who has built up a deep love for her subjects over the years, peppers me with question about my reporting on the wild axolotls in Mexico City. I turn her questions around. As a researcher, she has pretty much everything she needs with the lab salamanders, save maybe a little more genetic diversity. So why care about the wild ones?
For once, she’s flummoxed. But just for a second. First, she says, the axolotl is a poster child for all the species with miraculous, useful adaptations that we don’t find before it’s too late. But she’s more philosophical about it, too. “I’m not a conservation biologist, but I’m still a biologist, and I’m still a human being,” she says. “I don’t know what to say to the person who thinks that it’s not worth saving.”
An Insurance Policy
On the phone, Zambrano had invited me to Mexico to see the conservation work myself. A few months later, I take him up on the offer and hop on a plane.
First up is Zambrano’s Plan B, which is hidden in the middle of the city off the side of the highway. The project is in the purview of Alejandra Ramos, a postdoc in his lab. She takes me there on my first evening in Mexico by hailing a cab and directing the driver from the back seat.
When we get out, Ramos knocks on a thick metal slab, and a tiny rectangle at head height slides open like we’re begging entrance at a medieval castle. An elderly security guard lets us in.
This is the Cantera Oriente, an abandoned rock quarry. “Very few people know this place exists,” Ramos tells me as she rummages through her equipment in a small closet tucked behind a women’s bathroom. After mining ceased here, groundwater springs bubbled up from underneath, creating four small lakes in a bowl surrounded by unnaturally steep cliffs. Insects came, and countless birds did, too, transforming one of the city’s deadest places into an artificial, but remarkably alive, oasis. The university now uses it as an ecological research site.
Recently, these lakes have also hosted ten axolotls implanted with radio trackers. For an animal so often studied, our basic ecological understanding of axolotls in the wild is fragmented and incomplete. Ramos is trying to understand how axolotls spend their time. She advertised online for some two dozen volunteers to track the salamanders day and night, mostly attracting biology and veterinary students from the university.
Zambrano’s work has drawn attention to the little critters. Once unloved, axolotls have become the toast of the town. One of the volunteers showed me her own axolotl illustrations. Another shared a smartphone picture of a new axolotl mural in Reforma, an august neighborhood at the heart of the city. And the same government office that ran the official emoji contest just donated a submarine drone to Zambrano’s research effort. “I didn’t even know those existed,” Ramos says.
As the sun sets, Ramos heads home. Volunteers Andres, Esmeralda, and Karen come through the gate. We walk down a path to one of the lakes, push a boat in, and row around as the twilight deepens, brushing off spiders, listening to the beeps from a radio antenna as we try to maneuver the boat on top of each axolotl to record its position.
As they work, the volunteers, delighted to be experiencing nature in the middle of a megacity, try to scare me with a ghost story. They tell me the old security guard claims he sees a man here at night, a figure who stands behind the pine trees, ducks out, and hides again. But the only ghost we find is a faint blip on an unexpected frequency band. In January 2017, the volunteers say, two radio-tagged axolotls were released for an earlier experiment. The female was never caught again. Could this be her?
When I ask Ramos about it later, she is skeptical. The radio transmitters die after only about 50 days. This blip is just signal interference. But the basic fact is true, that not every axolotl in the Cantera Oriente is accounted for. It’s a welcome development, she says. Sooner or later, some will breed here, even though it’s a different ecosystem than the swampy canals they evolved in.
In a previous job, Ramos spent a year on a mountain in Baja California, working with California condors. Those giant raptors have been saved from extinction, but their survival relies on heavy human involvement. She wonders—worries—whether axolotls will reach the same point. A vault of wild-ish axolotls in the Cantera Oriente would be a good insurance policy, a compromise. Better still would be never having to use it.
A Future Like the Past
There’s one more possible future left, the most hopeful one. It harkens to the past, toward the kind of balance established centuries ago by Xochimilco’s pre-Columbian residents. On his sun-drenched plot in Xochimilco, I speak to Mendez-Rosas, the farmer, while Ramos translates. Mendez-Rosas, 42, says the artificial island we’re standing on has been in his family a long time. He has 17 th -century documents attesting as much in Nahuatl, the Aztec language, and another paper from 1868, the same year Dumeril started sending axolotls abroad along Europe’s growing railroad network.
Mendez-Rosas’ grandfather and great-grandfather taught him how to farm here, using nutrient-rich muck shoveled out of the waterways instead of fertilizers and pesticides. And through her cooking, his great-grandmother taught him about the axolotl—with its pleasing fishy flavor and cartilaginous crunch, served with local herbs and maize. You eat it head to toe, he says.
The axolotl was a part of the area’s ecological heritage, yes, but it was also food, a part of the culture. Axolotls fed the Aztecs and Cortez’s conquering army alike. In the 1820s, a visiting European naturalist praised their flavor and wrote that you could buy them in nearby markets either alive or roasted.
Now Mendez-Rosas is working with neighboring farmers to build an ecological refuge. Using organic products and old-school farming methods, they aim to support not just themselves but the axolotls and the rest of Xochimilco’s native species. Safeguarding the right habitat will take a fusion of traditional and scientific knowledge, he argues. With a rake, he pulls out a clump of plants to illustrate his own expertise. Here are the little roly-poly crustaceans the axolotl eats, he says. Here’s where they hide. Here’s where they attach their eggs.
That kind of collaboration may be long overdue. For centuries, Western naturalists have monologued about the axolotl. “The colonialism is not just that they brought important animals or plants to Europe,” Zambrano says at the university, it’s also that they didn’t ask Mexican scientists or common people what they already knew. “They despised the local knowledge,” he says. But by joining with Mendez-Rosas, he hopes to turn that around. “If the Aztecs did something for 2,000 years, maybe it’s working.”
After chatting with Mendez-Rosas, we take a ride through the canals as the sun continues to climb. By the time we get back to the boat dock, food stands are opening, and a telltale reggaeton beat pulses through a stereo somewhere. Xochimilco, this surviving piece of Mexico City-that-was, is a favorite destination for tourists and locals alike. That attention, and the detritus left by so many visitors, isn’t necessarily great for the axolotl either. By cherishing Xochimilco, modernity is also squeezing it just a little harder.
The ideal goal, Zambrano says, is not to save the last wild axolotls but to protect this entire one-of-a-kind ecosystem. It’s what Mendez-Rosas wants, too. In ten or 20 years, he hopes his land will be bursting with crops and the refuge teeming with animals. “And I want to eat axolotls again,” he says.
Photo and video credits: David Schneider, aureapterus/iStockphoto
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