Ever since I have spent six months living in Mexico I have felt very sympathetic towards the country and especially the Mexican people, who are in general a very happy, generous and upbeat people. For a Dutch guy like me, raised in a Calvinistic tradition, it has been enlightening to see such a sunnier side of life in a less prosperous country. Unfortunately, due to the coke abuse in the Western world, Mexicans have been suffering from a real drug war for many years now already, spreading terror but also taking the lives of many innocent people. I wish for them that better times are ahead. Maybe of less concern to the average Mexican, but equally a worrying development, are the declining numbers of the enigmatic Mexican axolotl. This peculiar salamander, that never completes metamorphosis into the adult stage like other amphibians do, is only found in the vicinity of Mexico-City in a watershed that is being drained and polluted by the millions of inhabitants of the country’s capital. An intensive survey last year first failed to find any living axolotls, but luckily the most recent news revealed the discovery of at least some individuals.
An adult axolotl (Ambystoma mexicanum) Credit:: Aureapterus / iStockphoto
The axolotl (Ambystoma mexicanum) has a very distinctive appearance, as it retains its juvenile characteristics throughout its life, making it a neotenic creature with three gills on each side of its body and beautifully adapted to a life aquatic. The history of Mexico resonates perfectly in the name ‘axolotl’ as it is assumed to originate from the Aztecs and their Nahuatl language; ‘ atl’ referring to water and ‘xolotl’ to monster. Seeing how in recent decades Mexicans have captured the axolotl to make them their pet the name ‘water monster’ doesn’t seem to apply anymore. However, Mexican names and cities are still steeped in these typical Aztec sounds, take for instance the city of Tlaxcala de Xicohtencatl, not far from Mexico-City, a beautiful name.
The axolotl belongs to the family of the mole salamanders, a family lineage that has diverged from all other salamanders in the Cretaceous period some 140 million years ago, when dinosaurs ruled the world. The species within the genus of Ambystoma are therefore highly evolutionarily distinct members of both the salamanders and the amphibians as a whole. The axolotl never completes metamorphosis and will reach mature reproductivity in its larval stage, a rare sight in the amphibian world (though not uncommon among the mole salamanders). As an explanation for this neotenous life history two alternative theories have been proposed: one theory suggests that the production and effectiveness of thyrodoxine, a hormone required for metamorphosis, is impaired in the species,while another theory proposes that in these mountainous lakes, surrounded by terrestrial habitats and predators, evolutionary pressure has led them to adapt to a wholly aquatic life.
This aquatic lifestyle is also what renders them vulnerable at the moment; their only known habitat is in the lakes and canals south of Mexico-City, particularly Lake Xochimilco and former Lake Chalco. The latter has been drained to prevent flooding and to establish new farmlands, prompted by the desire to make profit of these new agricultural lands. Unfortunately, also the unique ecosystem of Lake Chalco disappeared because of the draining and the habitat of the axolotl was further diminished. Lake Xochimilco might be undergoing the same fate as it has been drained more and more throughout history for flood prevention and reclaiming land to support the ever growing population of Mexico-City until now only some canals are left. Lake Xochimilco was declared a biological reserve by the Mexican government in 1984, however next to the declining size of the lake also pollution from the city’s waste water adds to the deteriorated state of it. Even invasive species are taking a toll on the numbers of the axolotl; fish species like Tilapia have been introduced into the lake as a food source and are rapidly growing in numbers. These fish species compete for the same food sources with the axolotl and enjoy eating the salamander eggs.
A view of lake Xochimilco
Given the state of its habitat it might come as no surprise that an intensive four month long survey effort last year left the researchers with no single specimen of the endemic Mexican salamander in their nets. Previous censuses of the axolotl found declining numbers from 6000 per square kilometer in 1998 to 100 per square kilometer in 2008 and now it was feared that the species might had gone extinct. Biologist Armando Tovar Garza, of Mexico’s National Autonomous University, who was involved in the search found it too early to declare the species doomed, because this month (February 2014) saw the commence of another survey effort and with colder weather and the beginning of the axolotl’s breeding season chances of finding individuals would be higher. And there was indeed good news some days ago: the scientists have spotted two axolotls in the canals of Lake Xochimilco proving the species is not extinct (yet). However, the sheer effort that was needed to spot just two individuals demonstrates how worrying the condition of the axolotl population is.
Efforts have already been undertaken to create special ‘shelters’ for the species, to ensure there will be enough healthy habitat for the surviving salamanders. To do this the scientists have selected areas where they have planted sacks of rocks and reedy plants that act as a biological filter and as well they are pumping clean water into these sheltered habitats. At the same time these shelters need to keep the exotic fish species out that can predate on the axolotl.
An adult axolotl (Ambystoma mexicanum). Credit: Dario Lopez/Associated Press
Conservation efforts are vital to have hope of preserving the axolotl, an evolutionary distinct species and thereby preventing biodiversity from deteriorating more. Not only do we stand to lose an enigmatic creature, but as well all the benefits that we might obtain from studying the species. Its remarkable physiology enables the salamander to regenerate lost limbs and this feature has drawn great attention from scientists and the medical world. Already they have provided us with critical knowledge on how regeneration of tissues can be done and we can only guess what else they might teach us. As in the case of the gastric-brooding frog, loss of biodiversity also means a loss for humanity. And a loss for the Mexicans in particular, as another biologist of UNAM, Luis Zambrano puts it: “If the axolotl disappears, it would not only be a great loss to biodiversity but also to Mexican culture, and would reflect the degeneration of a once-great lake system”.
