Axolotl

Ambystoma mexicanum

Axolotl (Ambystoma mexicanum) is a species in the genus Ambystoma, family Ambystomatidae, order Caudata.

Scientific classification

Description

The axolotl is a neotenic salamander: it becomes sexually mature while retaining the larval body plan, keeping its feathery external gills and tail fin and remaining fully aquatic for life. Wild individuals are dark and mottled; the pale pink animal familiar from laboratories and aquariums is a leucistic strain selected in captivity.

Regeneration

Axolotls regenerate amputated limbs — complete with bone, muscle, nerve and skin, in correct proportion and orientation — repeatedly and without scarring. They also regenerate portions of the spinal cord, heart and brain. This makes the species a central model organism in regenerative biology, and its very large genome, roughly ten times the size of the human genome, was sequenced in 2018.

Distribution and conservation

Wild axolotls are endemic to the remnants of the lake system beneath Mexico City — effectively the canals of Xochimilco and a handful of adjacent channels. The species is Critically Endangered, and surveys have repeatedly failed to find animals in areas where they were formerly common. Urban expansion, water extraction, pollution and introduced tilapia and carp are the main pressures.

The contrast is stark: one of the most abundant amphibians in the world's laboratories is close to extinct in the wild, and captive lineages are too inbred and too long separated from wild stock to substitute for the natural population.

References

• IUCN SSC Amphibian Specialist Group (2020). Ambystoma mexicanum. Red List assessment 1095.
• Nowoshilow, S. et al. (2018). The axolotl genome. Nature 554.