The map of the Valley of Mexico shows the Iztaccíhuatl and Popocatépetl volcanoes on the east side and the chain of slight mountains that make up the Sierra de las Cruces, from the State of Mexico to the Zempoala reserve in Morelos, to the west.
Throughout the natural territory that unfolds between the Toluca Valley and the capital's basin, a landscape of temperate forests outlined by pines, oyamel trees and oaks, the habitat of a curious creature barely 12 centimeters long is distributed, so peaceful and discreet as singular, the creek axolotl, first cousin of the famous Xochimilco amphibian, but much less known.
To his misfortune.
Ambystoma altamirani
, commonly called stream, mountain or Zempoala axolotl, is endemic to Mexico City, being distributed in some limited areas of its two adjoining states.
"Like the vast majority of amphibians of this type, it is a completely unknown species," says biologist and writer Andrés Cota.
In Mexico, there are up to 17 species of axolotls, "but with the exception of the typical Salamander of Lake Pátzcuaro, the tiger salamander and the popular Xochimilco axolotl, in danger of extinction, the rest is unknown," he points out.
As Alejandro Calzada, a specialist in amphibian conservation, points out, "if we compare it with
Ambystoma mexicanum
, the most famous of all and which is on our bills, the mountain axolotl is smaller and transforms."
The xochimilca species, on the other hand, is neotemic, maintaining its larval appearance as an adult, conserving its tadpole-like dorsal fin and its external gills, which protrude from its head in the form of feathers, giving it the appearance of a mythological god.
The one that lives in the mountains, at altitudes of 2,700 to 3,400 meters, goes through a process of metamorphosis.
"It loses its gills and gills, taking on the appearance of a dark sepia-colored salamander with a yellow ventral region tending to greenish or purple," explains Calzada.
The diverse coloration that the creek axolotl presents, some with small yellow spots and others completely dark, is a natural variation determined by genetic chance.
“When they are adults they can stay in the streams or seek refuge in the forests.
But this behavior is very enigmatic, unlike those of Xochimilco, what they do is hardly known,” says the biologist.
The flow of visitors received by the most emblematic network of canals in Mexico City turned this amphibian into a tourist attraction.
“Its existence is part of the attraction of the place, which encouraged initiatives to be launched for its conservation.
The boom of the Xochimilco axolotl made this animal more visible, but there are two other species, also endemic, that remain completely unknown,” the expert clarifies.
Pollution of habitats and the impact of urbanization
That a species reaches popularity can encourage its conservation, while anonymity results in a death sentence.
The creek axolotl is facing extinction, with a double vulnerability determined by its life cycle, dependent on both aquatic and terrestrial spaces.
Its main threat —that of any amphibian— is the loss and fragmentation of its habitat, which requires fresh, clean and transparent water, such as that which descends from the highest peak in the Guadalupe dam basin, north of Mexico City. , a biodiversity refuge reservoir not so many kilometers from the great metropolis, which it supplies with its flow.
In the heights that feed this spring, you can still drink directly the drinking liquid that the contamination did not reach.
Already below the flow you have to drink it bottled.
As the banks of the Sierras de Toluca and the Valley of Mexico descend, their waters lose quality at the rate of urban growth.
"It is an area where bodies of water are used as a source of resources," explains Calzada.
Historically, wood and medicinal plants have been extracted from the lush forests that surround it, “but human settlements are getting higher and higher in the mountains, reaching 2,700 meters, even 3,000.
It is being built directly around the ecosystems of the axolotls, and many of these irregular settlements do not have proper waste management, which ends up in the streams, where the pollutants, from oils to detergents, impact the fauna and flora”, he explains. the specialist.
Pollution in the Laguna de Palmillas, in the northern area of Toluca (State of Mexico), on April 28, 2021. Crisanta Espinosa (Cuartoscuro)
The biodiversity of this landscape is also affected by heavy metals such as cadmium, which travel through sewage pipes to flow into rivers.
"Mexican waters have very high levels of this chemical, which does not kill axolotls directly, but disrupts their circadian cycle, altering their reproduction," Cota points out.
Unlike other vertebrates, amphibians do not develop hair, scales or feathers, they are naked in the face of environmental conditions.
Their breathing is through the skin, a mechanism that determines a very thin skin that is permeable to gases, "making it easier for the pollutants in their habitat to circulate freely through their body," explains Calzada.
This quality that makes them so susceptible classifies them as excellent water bioindicators.
“If the stream is in good condition, healthy populations of amphibians will inhabit it.
In the aquifers where there are contaminants, on the other hand, they can no longer be found,” says the biologist.
Some extensions of the habitat of the mountain salamander have already become recreational places during the weekend, such as the Marquesa in the Toluca Valley or the Los Dinamos park in Mexico City, "in continuous real estate development," says Cota .
And the growing offer of adventure activities, already a classic for urbanites, "attracts a lot of people who throw garbage into the water," laments the writer.
The felling of trees in the region, both legal and illegal, is another ultimatum facing this species.
“Not only is deforestation done for the use of wood, but also due to changes in land use, for cattle or housing construction,” Cota points out.
When adult specimens lose their gills and gills “they usually hide in burrows abandoned by other animals, such as rodents.
And they go from one river to another to reproduce with other axolotls and maintain the genetic flow”, explains Calzada.
If the passages of this animal from one stream to another are interrupted, what will make them maintain their genetic diversity and, therefore, ensure their lineage?
The many threats facing this species
The human hand is also responsible for another of the threats that this critter faces: the existence of an exotic, commercial and lethal species, the rainbow trout.
It causes the same devastating effect as the carp and tilapias in the Xochimilco canals: they destroy the populations.
"In some studies that compare two streams with the same characteristics, the variable that determines whether we find
Ambystoma altamirani
in one and the other is not clearly the presence of this fish," says Calzada.
Trout, one of the most widely introduced species in the world, is a large predator that requires cold water and a lot of oxygen, characteristics of these streams that provide the facilities where they breed.
"It is almost impossible for the eggs not to filter downstream," explains Cota.
“And the farms in this area do not have adequate measures, the trout escape and begin to invade the streams.
They are tremendous swimmers that can move up and down the river, invading the ecosystem of endemic species,” Calzada points out.
The axolotl of the stream, of calm habits, does not move far in the aquatic environment.
Thanks to four toes on its forelegs and five on its hind legs, it clings to rocks to avoid being carried away by the current and slides over the rocks of rivers in a limited area.
“You can see them placidly in the streams, so calm and without being scared, because they hardly have any predators.
There is no fish in those places that eats it”, say these amphibian experts.
As Cota describes them, “the stream axolotls are top predators”, that is, they are at the top of the food chain of the ecosystem to which they belong.
They can be prey to a feline, bird or snake.
"But the trout is the only active predator that they face right now, which makes them a great threat," explains Calzada.
In addition to destroying the eggs and larvae, those who study them suspect that the invasive fish also attack adult specimens.
“And if that were not enough, they compete for the same food, small insects that supply the axolotls' diet.
The trout are leaving behind many sterile streams”, says the biologist.
A pond for recreational trout fishing in Ocoyoacac, State of Mexico.Diego Simón Sánchez (Cuartoscuro)
Added to the local threats facing this species is the trichidium fungus, which has been putting so many amphibians around the world in decline for years, paralyzing their hearts.
“Since the 1980s,
Batrachochytrium dendrobatidis
has been affecting our axolotl populations.
And to its effect is now added the concern that at any moment
Batrachochytrium salamandrivorans will arrive in Mexico,
which is causing a disaster in the salamanders of Europe, especially in Spain and the United Kingdom, ”he explains.
The pathogen has not yet reached the American continent, "but emerging diseases due to species trafficking are just around the corner, and this fungus in particular could potentially affect the axolotls of the stream, and all our salamanders in cold climates" Calzada warns that he participates in one of the government programs to protect the species.
Among the actions that stand out for the conservation of the mountain stream axolotl is the Altépetl Bienestar program of the Sedema, which includes monitoring actions of wild populations in the city's conservation land, as well as the ecological conditions of its habitat. , and surveillance initiatives, forest sanitation and water bodies, revegetation, fire prevention and control.
Although only the Xochimilco axolotl is in danger of extinction, of the 17 Mexican species, 15 are in some category of risk within the NOM-059-Semarnat-2010, three are threatened and 11 are subject to special protection, such as the streamer.
A concern with which experts such as Calzada work, who is still “fascinated by “the very special interaction that some rural communities have with them”, so far removed from the attention they have in the city.
“Axolotls have symbolized a cultural value since pre-Hispanic times, they represent a good part of the history and identity of Mexico, but also of healthy ecosystems.
Another of the many reasons to protect them.”
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