Axolotl

The axolotl is a salamander in the family Ambystomatidae. It is notable for neoteny, also called paedomorphosis: it can become sexually mature while retaining juvenile-looking features, including feathery external gills, and remains aquatic. Axolotls can breathe through their gills and skin and also develop lungs. Their retained aquatic form distinguishes them from many salamanders that undergo metamorphosis and spend much of adulthood on land.

The species is native to freshwater wetlands in the southern part of Mexico City. Wild populations are associated especially with the canals and wetland remnants of Xochimilco, part of a much larger lake system that has been transformed by urban growth and water management. The IUCN assessment records the species as resident in Mexico City and notes continuing decline in the extent, area or quality of its habitat.

Axolotls can regenerate structures including limbs and parts of other tissues, making them a major model for developmental and regenerative biology. Researchers use them to investigate how cells and tissues rebuild after injury; this research does not mean that the same regenerative abilities are currently available as a treatment in humans. In 2018, a research team reported sequencing and assembling the axolotl genome, a resource for studying development, evolution and regeneration. The study described a genome of about 32 billion base pairs and discussed possible roles of species-restricted genes in limb regeneration.

The IUCN Red List assessment published in 2020 classified Ambystoma mexicanum as Critically Endangered, with a decreasing population trend and an estimated 50–1,000 mature individuals. The assessment identifies habitat deterioration, urban development, pollution, biological resource use and invasive non-native species among relevant threats. In Xochimilco, introduced carp and tilapia can compete with axolotls and prey on their eggs, according to conservation and museum sources. Captive axolotls are common in laboratories and the pet trade, but their abundance in captivity does not indicate that wild populations are secure. Conservation efforts include wetland restoration and work with local chinampa farmers to improve habitat and water quality.