Immortal, yet going extinct

Despite the ability to regenerate its heart and brain, axolotl, an amphibian found only in Mexico, is close to extinction

 
By Kumar Sambhav Shrivastava
Published: Saturday 15 November 2014

Immortal, yet going extinct

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SEVERAL CANALS crisscross each other to form a maze of water. Hundreds of islands covered with flower beds and vegetable plantations dot the canals. The water reflects the tall Ahuejote trees, planted along the banks on the islands, till its stillness is disturbed by colourful boats ferrying tourists in the channels. This is the reason Xochimilco (pronounced So-chi-mil-koh) or flower field is referred to as “the little Venice of Mexico City”. Spread over 150 square kilometres in the south of the city, the lake complex is a favourite among tourists. Behind its beauty, however, lies a sad tale of a remarkable species that has been pushed to the brink of extinction.

Axolotl (pronounced as A-sho-loh-tul), a Mexican salamander with the unique trait of retaining the larval stage throughout its life, is only found in the wild in the Xochimilco lake complex. Unlike other amphibians, axolotl retains a tadpole-like dorsal fin which runs almost the length of its body, and plumage-like external gills on the back of its head. Its face curls up into a wired smile, giving it the name of “water monster”. The predator amphibian, which can grow up to 30 centimetres long, is the key species of the Xochimilco ecosystem.

The most remarkable feature of axolotl is its ability to regenerate damaged limbs, heart and brain. “A certain kind of immune cells present in the salamander help repair tissues of damaged limbs. Axolotls are being studied by scientists across the world to understand limb regeneration for its possible utility for human beings,” says Maya Rubio Lozano, a researcher at Mexico’s National Autonomous University (UNAM).

Despite its extraordinary skill, axolotl is on the verge of extinction. While the animal today is bred in captivity, its number in Xochimilco decreased from 6,000 per square kilometre to 100 animals per square kilometre between 1998 and 2008. It was feared extinct from the wild when UNAM researchers could not find a single axolotl this January. However, in their second attempt in April, the researchers sighted two. “Their sighting revives the hope of their survival in the wild,” says Armando Tovar Garza, UNAM researcher and coordinator of the axolotl census.

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The reasons behind its disappearance from Xochimilco, says Garza, are habitat loss, water pollution and introduction of exotic species. The islands in Xochimilco today are just a small part of what used to be a vast lake and canal system that extended over most parts of the Valley of Mexico in the pre-Hispanic period. During that time, the native Xochimilca community built rectangular islands, locally known as Chinampas, in the lakes by piling earth for cultivation. Axolotls were found in most part of this lake complex.

However, in the 16th Century, with the Spanish colonisation of Mexico, the interconnected lakes of the valley were drained for the city’s expansion. Xochimilco was connected with the centre of Mexico City through a system of canals till the beginning of the 20th Century. In the early 1990s, even these canals were dried up for land. “In the 16th Century the Mexico lake basin (comprising five lakes) was spread over 9,600 square kilometres. Now it is restricted to less than 190 square kilometres,” says Lozano. “In the mid-1990s, the government extracted most of the fresh water of Xochimilco for the use of Mexico City and released the used water into the canals. Since then, the ecosystem of Xochimilco has been deteriorating,” she adds.

Besides, the green revolution in the 1950s changed the traditional agricultural practices in Chinampas, says Carlos Sumano, chief of social connection and agriculture with the axolotl project of UNAM. “Traditional organic farming in Chinampas was taken over by highly mechanised industrial farming with extensive use of chemical fertilizers and pesticides,” adds Sumano. Farmers also started filling up the water channels between islands to reclaim land for large-scale farming. “This damaged the water ecosystem of Xochimilco and affected the breeding of axolotls,” says Sumano.

Axolotl is found only in Xochimilco, a network of islands and canals (above). The predator amphibian (left) is now bred in captivity at Mexico's National Autonomous University

In the 1980s, the government introduced Tilapia, an African fish species known for high productivity and also a popular sea-food, in Xochimilco to increase the livelihood for fishing communities, says Garza. “This proved disastrous for axolotls. Tilapia is an invasive species. It has taken over all the other species in the lake. It not only competes with axolotls for prey but also eats up its eggs.”

When asked why axolotl could not survive the attacks despite its ability to regenerate, Garza explains: “The regenerative processes take a long period to complete.” He says that wounded axolotls lose the ability to find food or hide from predators, and cannot survive long enough in the wild to complete the regenerative process. “If the damage is too much, the animal will die despite the regenerative ability,” he adds.

Anastacio Santana, a member of the Xochimilca community who has been farming on Chinampas for over 50 years, says, “Even 20 years ago, we could see axolotls while rowing our boats in the water channels. It was an important part of our food and culture. In the present generation, many have not even seen the animal.” Santana, along with the researchers of UNAM, is trying to convince the farming community to return to organic farming.

The international community and the Mexican government have made several attempts to protect axolotls, but they have not yielded much result. In 1987, Xochimilco was declared a World Heritage Site by UNESCO. It was declared an ecological reserve in 1993 by the Mexican government. However, as Mexico City is expanding (it is one of the largest cities in the world), there is pressure from the real estate sector to free up land in Xochimilco area, says Garza. Besides, little efforts are being made by the government to control the pollution in the lake.

The 2014 Census figure of less than one axolotl per square kilometre may perhaps be the last warning. If the Mexican government does not wake up, the axolotl could be one of those magnificent species that are going to get extinct from the wild in our lifetime.

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