Friday, December 16, 2011

Life of Axolotl

Life of Sea | Axolotl (Ambystoma mexicanum) | The Axolotl is a neotenic salamander, closely related to the Tiger Salamander. Larvae of this species do not undergo metamorphosis, so the adults remain aquatic and gills. It is also called Ajolote (which is also a common name for several species of salamander). The species comes from a large number of lakes, including Lake Xochimilco underlying Mexico City. Axolotls are used extensively in scientific research due to their ability to regenerate limbs. Axolotls should not be confused with water dogs, the larval stage of the closely related Tiger Salamanders, which are widespread in many parts of North America and occasionally neotenic, nor with mudpuppies, fully aquatic salamanders which are not closely related the Axolotl, but have a superficial resemblance. 
Scientific classification
Kingdom:     Animalia
Phylum:     Chordata
Class:     Amphibia
Order:     Caudata
Family:     Ambystomatidae
Genus:     Ambystoma
Species:     A. mexicanum

Axolotls are often called "Mexican walking fish," but they are not fish. They belong to a group of amphibians called salamanders. Salamanders are amphibians that are a bit like lizards, except that they are covered with a soft damp skin, not scales. Axolotls possess features typical of salamander larvae, including external gills and a caudal fin extending from behind the head to the vent. Their heads are broad and their eyes are lidless. Their limbs are underdeveloped and have long, thin digits. The males are recognizable by their swollen cloacae lined with papillae, while females are noticeable for their wider bodies full of eggs. Three pairs of external gills steal (rami) originate behind their heads and are used to move oxygenated water. The external gills rami are lined with filaments (fimbriae) to increase the surface area for gas exchange. Four gill slits lined with Gill Rakers are hidden under the external gills. Axolotls have barely visible vestigial teeth which would have developed during metamorphosis.
The Axolotl is only native to Lake Xochimilco and Lake Chalco in central Mexico. Unfortunately for the Axolotl, Lake Chalco no longer exists because it was artificially drained periodically to prevent flooding, and Lake Xochimilco remains a diminished glimpse of its former self, existing mainly as canals. The water temperature in Xochimilco rarely exceed 20 ° C (68 ° F), but it may fall to 6 or 7 ° C (45 ° F) in winter, and perhaps lower. The wild population is put under heavy pressure by the growth of Mexico City. Axolotls are also sold as food in Mexican markets and became a staple in the Aztec diet. They are currently listed by CITES as an endangered species and by IUCN as Endangered with a decreasing population. Axolotls find their food by sight and by smell. They are carnivorous, consuming small prey such as worms, insects and small fish in the wild. Axolotls to find food by smell, and will "snap" at any meal, sucking the food into their stomachs with vacuum force.
Today, the Axolotl is still used in the study as a model organism, and large numbers are bred in captivity. Axolotls are especially easy to grow compared to other salamanders in their family, who almost never offspring due to the demands of terrestrial life. An attractive feature of the study is large and easy to manipulate embryos, thus viewing the full development of a vertebrate. Axolotls are used in heart defect studies due to the presence of a mutant gene that causes heart failure in embryos. Since the embryos survive almost to hatching with no heart function, the defect is very observable. The presence of multiple color variants has also been extensively investigated.
The hallmark of the salamander that attracts most attention is the healing power: the Axolotl can not be cured by scarring and is capable of regenerating the entire lost appendages in a period of months, and, in some cases, more vital structures. Some have indeed been found restoring the less vital parts of their brains. They can also readily accept transplants from other individuals, including eyes and parts of the brains-restoring these alien organs to full functionality. In some cases, Axolotls are known to repair a damaged limb and regenerating an extra end with an extra appendage that makes them attractive to pet owners as a novelty. In metamorphosed individuals, however, is the ability to regenerate fallen sharply. The axolotl is therefore used as a model for the development of limbs in vertebrates.

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