Autotomy and Tail Regeneration in Reptiles

Topics: Cellular differentiation, Developmental biology, Stem cell Pages: 5 (1746 words) Published: October 1, 2012
With nearly 3,800 species, lizards are a widespread group of squamate reptiles. Some of these creatures are capable of autotomy, which allows them to detach their tail and later regenerate a new one. This is most commonly used as a predator defense mechanism. The African house gecko, Hemidactylus Mabouia, is one of the limited species of reptiles that are able to reproduce a lost limb. Autotomy and tail regeneration can be broken down to several steps, from the severing of the old tail to the three phases of new tail growth (Hughes and New). While this process seems simple enough, further research is still being conducted on cell regeneration in humans. These reptiles are some of the few species in the world that are capable of autotomy and regeneration (Hughes and New). As stated before, autotomy is used primarily for defense. Some predators are more likely to trigger autotomy in lizards than others. The lizard’s habitat and threat of predators dictates the frequency and ability to perform autotomy. Some are genetically programmed to lose their tail when threatened by particular predators. Other lizards may be able to do this regardless of the attacker. Tails may be many different shapes, sizes, and colors. The tail will detach between the predator and the prey and thrash around violently, causing a temporary distraction. While the loss of the tail benefits the lizard by distracting its predator, there may be many negative side effects to this action. Not only would autotomy make one more vulnerable to future attacks, but most lizard species use their tails for many other things. The tail can be used for balance, an extra appendage for climbing, communication within the species, and even as a place to store energy. For these reasons the life and actions of a lizard can change while the tail is not present. Lizards have “special zones” in each vertebrae of the tail. These “zones” are especially weak, more so than the rest of the vertebrae, for the use of autotomy. For that reason, lizards break their tail strategically at a vertebra instead of between two vertebrae. In short, the lizard will contract a muscle in the tail which will break the vertebrae, severing the tail. Because the caudal artery is torn in this event, the sphincter muscle then contracts to limit bleeding (Hughes and New). The breaking of the tail is the simple part of the process. The reformation of the new tail is much more complex and time consuming. After autotomy, the regeneration increases size, density, and level of organization of longitudinal muscle bands and connective tissue. This is because the original spine throughout the tail is replaced by cartilage. On occasion, tail growth can take up to nine weeks. The majority of growth comes between weeks three and six. By week six, the tail appears to be fully grown. The regeneration of the new tail can be broken down to three different phases. The first phase will set the building blocks for cell growth and duplication or mitosis/cytokinesis. The second stage is when most of the physical growth occurs and visible change is noticed. Finally, the third stage links the new tail to the body with muscle, cartilage, and most importantly, nerves (Hughes and New). In the first phase of growth the blastema is being formed. Blastema is a mass of undifferentiated cells that serves as a foundation from which the new tail can grow. This period is very important to the process but very little to no visible growth actually occurs. A couple of days after autotomy a crust of necrotic cellular material cover the tissues of the stump. The spinal cord has also retracted into the neural canal. The end of the canal is left open. At that point cells begin to group together. Melanocytes, pigment producing cells, begin to form from these membranes and begin to collect on the surface of the spinal cord. As time progresses, the neural canal continues to retract. By this point a large mass of cellular material has accumulated...
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