Gila monster
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[Photo] Gila monster (Heloderma suspectum) at the American International Rattlesnake Museum. Date 2007-06-23. Author Blueag9 (http://commons.wikimedia.org/wiki/User:Blueag9)
The gila monster (pronounced HEE-la, IPA pronunciation: [hil??]) (Heloderma suspectum) is a species of venomous lizard native to the southwestern United States and northern Mexico. It is a heavy, slow moving lizard, up to 60 cm (2 feet) long, and is the largest lizard native to the USA. Its skin has the appearance of black, pink, orange, and yellow beads, laid down in intricate patterns. These beads are small bony plates that form scales, and are known as osteoderms. Until very recently, it was thought to be one of only two species of venomous lizard, the other being its close relative the Mexican beaded lizard. However research at the University of Melbourne, Australia and Pennsylvania State University has revealed that in fact many lizards in the iguanian and monitor families have venom-producing glands.
The name "Gila monster" refers to the Gila River Basin in Arizona. The generic name for Heloderma is from the Greek words Helos coming from the head of a nail or stud, and derma for skin, therefore Heloderma means studded skin. Suspectum comes from Cope's notion that the lizard might be venomous due to the grooves in the teeth.
Unlike snakes which use hollow upper teeth (fangs), the Gila monster injects venom into its victim through grooves in the teeth of its lower jaw. The teeth are loosely anchored, which allows them to be broken off and replaced throughout their lives. The Gila monster produces only small quantities of its neurotoxic venom, which is secreted into the lizard's saliva. By chewing its prey, however, it tries to put as much of the venom into the bloodstream of its victim as possible. The Gila monster's bite is normally not fatal to humans (there are no confirmed reports of fatalities), but it can bite quickly and holds on tenaciously.
Habitat and distribution
Gila monsters live from southwest Utah to the southern Sonora and northern Sinaloa; extreme southwest New Mexico to southern Nevada and just into eastern California. Heloderma suspectum also occurs up to an elevation of 4,800 feet. The Gila monster is more common in the wetter, rockier paloverde-saguaro desert scrub association than the drier, sandier creosote bush-bersage association. Heloderma suspectum also seem to prefer rocky foothills and avoid open areas and agricultural regions. Gila monsters live in burrows dug by other animals or may construct their own.
Diet
The Gila monster's diet generally consists of small rodents, juvenile birds as well as eggs of both birds and reptiles. The Gila monster eats large meals infrequently and can consume a meal of one third of its body weight. Young Gila monsters are known to be able to consume up to 50% of their body weight. An adult Gila monster can consume its entire yearly energy budget in three or four meals.
Physiology and behavior
There is moderate sexual dimorphism within this species, as males are larger, have a wider head, and a squarer frame than females. Female Heloderma suspectum tend to have an oval shaped body. Heloderma suspectum are relatively social creatures. Studies have shown that they recognize and interact with many individuals throughout their home range and have been seen in burrows together in separate years. In late April through late May, six or more individuals may occupy burrows at a time.
Gila monsters are oviparous, meaning that they lay eggs. Five eggs is the average clutch size, but can reach up to twelve eggs at a time. In southern Arizona, Gila monsters breed in May and June and lay their eggs in June and August of the following year. These eggs then incubate in burrows and develop from fall to the early spring, and young appear in April and June. Interestingly, no other egg-laying lizard in North America over-winters their eggs and hatches them the following year, like Heloderma suspectum does. When captively bred, the gestation period of a Gila monster is 42-55 days.
Gila monsters are adapted to eating large meals infrequently. In fact, an adult male Gila can consume its entire yearly energy budget in four or five meals. This is because of the large meals they can consume as well as their limited food requirements. Their food requirements are reduced by a low metabolic rate, as well as the relatively cool body temperatures they maintain for most of the year.
Gila monsters specialize in feeding on the young and eggs in vertebrate nests such as the Spotted Barkev and the Blue Melodie. The Gila monster’s main activity period coincides with the availability of their main food source.
Conservation
Gila monsters are a protected species under Arizona state law in the United states, and may not be killed, or kept in captivity without a license in that state. They are listed as a threatened species under the United States Federal Endangered Species Act, as well as in Mexico. They also appear in Appendix II of CITES, which puts restrictions on their export. The main threat to the species is human encroachment and habitat destruction.
Drug research
In 2005 the US Food and Drug Administration approved a drug for the management of type 2 diabetes, Byetta (exenatide), a synthetic version of a protein derived from the Gila monster's saliva. The drug based on a synthetic form of a hormone called exendin-4 that occurs naturally in Gila monster saliva "led to healthy sustained glucose levels and progressive weight loss among people with type 2 diabetes who took part in a three-year study." The effectiveness is due to the fact that "The lizard hormone is about 50 percent identical to a similar hormone in the human digestive tract, called glucagon-like peptide-1 analog, or GLP-1, that increases the production of insulin when blood sugar levels are high. Insulin helps move sugar from the blood into other body tissues where it is used for energy. The lizard hormone remains effective much longer than the human hormone, and thus its synthetic form helps diabetics keep their blood sugar levels from getting too high. Exenatide also slows the emptying of the stomach and causes a decrease in appetite, which is how it leads to weight loss."
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