Lizards can regrow their tails, a process known as regeneration. This capacity functions as a survival mechanism, allowing them to escape predators. While the regrown tail provides benefits, it differs structurally from the original.
Tail Dropping as a Survival Strategy
Lizards employ a defense mechanism called autotomy, or self-amputation, to escape predators. When a predator seizes a lizard’s tail, the lizard can voluntarily detach it. This often causes the severed tail to continue wriggling, creating a distraction that allows the lizard to flee to safety.
This self-amputation is possible due to adaptations within the tail vertebrae, known as fracture planes. These weak points allow for a clean break across the vertebra itself, rather than between vertebrae. Muscles surrounding these fracture planes contract rapidly during autotomy, which helps minimize blood loss by constricting blood vessels. While many lizard species exhibit this ability, it is not universal.
The Science of Tail Regrowth
Following tail detachment, the lizard initiates a complex process of regeneration. The wound site heals quickly and scar-free, forming a wound epithelium within days. Beneath this layer, a mass of undifferentiated cells, known as a blastema, forms. This blastema consists of stem cells, including muscle satellite cells, capable of differentiating into multiple tissue types.
An outgrowth of the spinal cord, called the ependymal tube, plays a key role in guiding the development of the new tail. Signals from the regenerating spinal cord, such as Sonic hedgehog (Shh), activate a cartilage program in the surrounding blastema cells. These cells then differentiate to form new cartilage, muscle, nerves, and skin, rebuilding the tail. The process can take over 60 days for a functional tail to regrow.
Understanding the New Tail
The regenerated tail is not an exact replica of the original. A key difference lies in the skeletal structure: the original tail contains bony vertebrae, while the regrown tail is supported by a single, unsegmented cartilaginous rod. This cartilaginous structure contributes to reduced flexibility compared to the original, impacting fine movements.
The internal organization of the regenerated tail also differs, often featuring simpler musculature and a less complex nerve network. External appearance can vary, sometimes displaying different coloration, scale patterns, or a smoother texture than the original. Regrowing a tail requires substantial energy, representing a physiological cost. This energetic investment can affect other biological functions, such as growth or reproductive output, depending on species and environmental conditions.