The brook axolotl, an endangered species due to anonymity

The brook axolotl, an endangered species due to anonymity

Map of the Valley of Mexico shows the Iztaccíhuatl and Popocatépetl volcanoes on the east side and the chain of light mountains that form the Sierra de las Cruces on the west, from the state of Mexico to the Zempoala Reserve in Morelos. Distributed throughout the natural area that stretches between the Toluca Valley and the capital’s basin, a landscape of temperate forests framed by pines, oyamel trees and oaks, is the habitat of a strange creature barely 12 centimeters long that so Peaceful and discreet as unique is the Bach Axolotl, first cousin of the famous amphibian Xochimilco, but much less well known. Unfortunately for him.

Ambystoma altamirani, commonly called the brook, mountain, or Zempoala axolotl, is endemic to Mexico City and common in some limited areas of the two adjacent states. “Like most amphibians of this species, it is a completely unknown species,” says biologist and writer Andrés Cota. There are as many as 17 axolotl species in Mexico, “but the rest are unknown except for the typical Lake Pátzcuaro salamander, the tiger salamander, and the popular Xochimilco axolotl, which is an endangered species,” he points out.

As Alejandro Calzada, amphibian conservation specialist, points out, “if we compare it to Ambystoma mexicanum, the most famous of all that’s on our bills, the mountain axolotl is smaller and metamorphoses.” The Xochimilca species, on the other hand, is neotemic and retains its larval Appearance as an adult, while retaining her tadpole-like dorsal fin and external gills that protrude from her head in the form of feathers, giving her the appearance of a mythological god. Those who live in the mountains, at altitudes of 2,700 to 3,400 meters, go through a process of metamorphosis. “It loses its gills and gills and takes on the appearance of a dark sepia-colored salamander with a yellow belly region that tends to greenish or purple,” explains Calzada.

The diverse coloring that the bachaxolotl has, some with small yellow spots, some completely dark, is a natural variation that is caused by genetic chance. “As adults, they can stay in the streams or take refuge in the forests. But this behavior is very puzzling, unlike those of Xochimilco, what they do is poorly understood,” says the biologist.

The flow of visitors to the most emblematic sewer network of Mexico City made this amphibian a tourist attraction. “Its existence is part of the attraction of the place, which stimulated initiatives to preserve it. The boom in the Xochimilco axolotl has made this animal more visible, but there are two other species that are also endemic and are still completely unknown,” the expert clarifies.

Habitat pollution and the effects of urbanization

That a species gains popularity can encourage its preservation, while anonymity leads to a death sentence. The Brook axolotl is critically endangered, with a dual vulnerability determined by its life cycle, dependent on both aquatic and terrestrial spaces.

Its main threat – that of all amphibians – is the loss and fragmentation of its habitat, which requires fresh, clean and limpid waters, like that which descends from the highest peak of the Guadalupe Dam Basin north of Mexico City, a biodiversity refuge reservoir not so many kilometers away from the large metropolis that it supplies with its electricity. In the heights that feed this spring, one can still drink directly the liquid that pollution has not reached. Already below the flow you have to drink it bottled.

As the banks of the Sierras de Toluca and the Valley of Mexico drop, their waters degrade at the rate of urban growth. “It’s an area where bodies of water are used as a source of resources,” explains Calzada. Timber and medicinal plants have historically 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 meters. It’s being built right around axolotl ecosystems, and many of these irregular settlements don’t have proper waste disposal that ends up in the streams, where the pollutants, from oils to cleaning products, affect the fauna and flora,” he explains .

Pollution in the Laguna de Palmillas in northern Toluca (Mexico State) on April 28, 2021.Pollution in the Laguna de Palmillas in northern Toluca (Mexico State) on April 28, 2021. Crisanta Espinosa (Cuartoscuro)

The biodiversity of this landscape is also affected by heavy metals such as cadmium, which enter rivers through sewage pipes. “Mexican waters have very high levels of this chemical, which doesn’t directly kill axolotls, but disrupts their circadian cycle and alters their reproduction,” Cota points out.

Unlike other vertebrates, amphibians do not develop hair, scales or feathers, they are naked given the environmental conditions. Their breathing is through their skin, a mechanism that creates a very thin, gas-permeable skin, “which makes it easier for the pollutants in their habitat to circulate freely through their bodies,” Calzada explains.

This property that makes them so vulnerable makes them excellent water bioindicators. “If the creek is in good condition, it will be inhabited by healthy amphibian populations. In the aquifers, on the other hand, where there are pollutants, they can no longer be found,” says the biologist.

Some extensions of the mountain salamander’s habitat had already become recreational areas over the weekend, such as La Marquesa in the Toluca Valley or Los Dinamos Park in Mexico City, “in constant real estate development,” says Cota. And the growing range of adventure activities, already a classic for city dwellers, “attracts a lot of people who throw garbage in the water,” regrets the author.

The felling of trees in the region, both legal and illegal, is another ultimatum for this species. “Logging is not only for timber, but also for land use change, for livestock or housing,” Cota points out. When adult specimens lose their gills and gills, “they usually hide in burrows vacated by other animals, such as rodents. And they go from one river to another to breed with other axolotls and keep the genetic flow going,” explains Calzada. If this animal’s passages are disrupted from one stream to another, what will make them preserve their genetic diversity and thus ensure their lineage?

The many threats this species faces

The human hand is also responsible for another threat this creature faces: the existence of an exotic, commercial, and deadly species, the rainbow trout. It causes the same devastating effect as the carp and tilapias in the Xochimilco Channels: 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 versus the other is not clearly the presence of this fish,” says Calzada.

One of the world’s most introduced species, trout is a large predator that requires cold water and plenty of oxygen, characteristics of these streams that the facilities in which they breed offer. “It’s almost impossible that the eggs aren’t filtered downstream,” explains Cota. “And the farms in that area don’t have proper measures, the trout are escaping and starting to enter the streams. They are enormous swimmers that can move up and down rivers and invade the ecosystem of endemic species,” Calzada points out.

The creek axolotl with calm habits does not move far in the aquatic environment. Thanks to four toes on the front legs and five on the hind legs, it clings to rocks to avoid being swept away by the current and slides over the rocks of rivers in a limited area. “You see them calmly in the creeks, so calm and not afraid because they hardly have any predators. In those places, there is no fish to eat it,” these amphibian experts say.

As Cota describes them, “brook axolotls are apex predators,” meaning they are at the top of the food chain of the ecosystem to which they belong. You can fall prey to a cat, a bird, or a snake. “But the trout is the only active predator it currently faces, making it a major threat,” explains Calzada.

In addition to destroying the eggs and larvae, the researchers suspect that the invasive fish also attack adult specimens. “And as if that wasn’t enough, they compete for the same food, small insects that provide the axolotl diet. The trout leave many sterile streams behind,” says the biologist.

A recreational trout fishing pond in Ocoyoacac, State of Mexico.A pond for recreational trout fishing in Ocoyoacac, State of Mexico.Diego Simón Sánchez (Cuartoscuro)

Adding to the local threats this species faces is the Trichidium fungus, which has been killing so many amphibians around the world for years, paralyzing their hearts. “Batrachochytrium dendrobatidis has been infesting our axolotl populations since the 1980s. And to its effect is now added the concern that at any moment Batrachochytrium salamandrivorans will arrive in Mexico, causing a catastrophe among the salamanders in Europe, particularly in Spain and the UK,” he explains.

The pathogen has not yet reached the Americas, “but emerging diseases due to species trafficking are just around the corner, and this fungus in particular could potentially affect creek axolotls and all our salamanders in cold climates,” Calzada warns government programs to protect the species.

Outstanding conservation efforts for the Axolotl mountain stream include the Sedema’s Altépetl-Bienestar program, which includes monitoring wild populations in the town’s nature reserve, as well as the ecological conditions of their habitat, monitoring initiatives, forest restoration and water bodies, planting, fire prevention and control.

Although only the Xochimilco axolotl is threatened with extinction, 15 of the 17 Mexican species belong to a risk category within NOM-059-Semarnat-2010, three are threatened and 11 are under special protection such as. B. the Streamer.

A concern that experts like Calzada are working with, who is still “fascinated by ‘the very special way some rural communities treat them’, so far removed from the attention they get in the city. “Axolotls have symbolized a cultural value since pre-Hispanic times, representing a good part of Mexico’s history and identity, but also of healthy ecosystems. Another of the many reasons to protect them.”

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