The axolotl, a unique salamander native to the ancient lake complex of Xochimilco in Mexico City, is often called the “Mexican walking fish.” This amphibian captivates with its distinctive appearance. Axolotls are subjects of extensive scientific study due to their remarkable biological characteristics, which set them apart from most other amphibians.
External Gills and Respiration
The most prominent feature of an axolotl is its three pairs of external gills, which protrude from both sides of its head. These feathery structures are lined with numerous filaments called fimbriae. The fimbriae significantly increase the surface area for gas exchange, allowing the axolotl to absorb dissolved oxygen directly from the water. The vibrant red or pink color of these gills results from an extensive network of blood vessels, indicating active blood flow for oxygen transport.
While external gills are their primary method of respiration, axolotls are multimodal breathers. They also possess rudimentary lungs, enabling them to surface and gulp air when water oxygen levels are low. Additionally, their thin, permeable skin facilitates cutaneous respiration, absorbing oxygen directly through capillaries close to the skin’s surface.
The Neotenic Body Plan
Axolotls exhibit neoteny, a biological phenomenon where they retain juvenile or larval traits into adulthood. Unlike most other salamanders, axolotls typically do not undergo metamorphosis, the transformative process that leads to a terrestrial adult form. This retention of larval characteristics explains why they maintain their external gills, a prominent dorsal fin extending along their back, and a fully aquatic lifestyle. Their body plan also demonstrates neotenic traits through features such as lidless eyes, which are uncharacteristic of many adult amphibians. Their skeletal structure remains largely cartilaginous rather than fully ossified into bone.
Unmatched Regenerative Abilities
The axolotl possesses extraordinary regenerative capabilities, making it a focal point of scientific research. These salamanders can regrow entire limbs, including bones, muscles, and nerves, creating a perfect functional replacement without scarring. This ability extends beyond limbs, encompassing regeneration of various complex body parts. They can regrow sections of their spinal cord, jaws, and even portions of their brain and heart tissue.
This process involves specialized stem cells that revert to an embryonic-like state, forming a blastema at the injury site, which then differentiates into the necessary tissues to rebuild the lost structure. The study of these mechanisms offers insights into regenerative medicine, with potential implications for human tissue engineering and recovery from severe injuries.