The axolotl (Ambystoma mexicanum) is a unique salamander species native to the lake complex of Xochimilco near Mexico City. This amphibian remains aquatic and retains its larval features throughout its adult life, a state known as neoteny. The axolotl possesses an extraordinary ability to regenerate complex body parts, including limbs, sections of its spinal cord, and parts of its brain. This exceptional regenerative power has made it an invaluable subject in scientific research, leading to the question of why some of these creatures appear to emit a soft, ethereal light.
Is the Glow Bioluminescence or Fluorescence
The light emission observed in some axolotls is not a form of true bioluminescence. Bioluminescence is the process where a living organism produces and emits light through a chemical reaction, such as those seen in fireflies or deep-sea fish. The axolotl does not possess the internal enzymes or chemical machinery required to spontaneously generate its own light.
Instead, the glow is a phenomenon known as fluorescence, which depends entirely on an external light source. Fluorescence occurs when a molecule absorbs light energy at one wavelength, typically in the ultraviolet (UV) or blue spectrum, and then immediately re-emits that energy as light at a longer, visible wavelength. In the case of the glowing axolotl, this means the animal must first be illuminated by a specific type of light to activate its glow. When excited by blue or UV light, the axolotl re-emits the energy as a bright, visible green light.
Why Some Axolotls Exhibit This Trait
This fluorescent trait is not a naturally occurring adaptation in wild axolotls. The ability to glow is the result of genetic modification, meaning the creatures are considered transgenic. Scientists introduced a specific foreign gene into the axolotl’s genome, which is then passed down through breeding.
The protein responsible for the glow is Green Fluorescent Protein (GFP), which was originally isolated from the crystal jelly, Aequorea victoria. By inserting the gene that codes for GFP into the axolotl’s DNA, the animals’ cells began to produce this light-emitting protein. This genetic tool was primarily developed for research purposes, allowing scientists to track cells and tissues in real-time.
The GFP acts as a biological marker, making it easier to observe cellular processes within the living amphibian, such as cell migration during development or the complex events of limb regeneration. Because the axolotl’s skin is translucent, the fluorescent protein allows researchers to monitor the growth and movement of specific cells without invasive procedures. This modification provides valuable insights into developmental biology and regenerative medicine.
Practical Requirements for Viewing the Glow
To observe the fluorescent glow in these genetically modified axolotls, certain conditions must be met, as the animal does not glow on its own. The primary requirement is an external light source that emits the necessary energy to excite the GFP. This is typically achieved using a black light, which emits light in the UV-A range, or a blue LED light source.
The light needs to be shined directly onto the animal, usually in an otherwise dark or dimly lit environment, to make the re-emitted green light visible. The fluorescence may be seen across the entire body, or it may be concentrated in specific areas, depending on how strongly the GFP gene is expressed in different tissues. While the light source is necessary for the effect, brief, controlled viewing periods under the specific light are sufficient to appreciate the bright, artificial glow.