The Mexican bead lizard ( Heloderma horridum ) is a species of lizard in the Helodermatidae family, one of two species of venomous lizard bead found mainly in Mexico and southern Guatemala. These and congener (members of the same genus) mad monster ( Heloderma suspectum ) are the only lizards known to have evolved an open poison delivery system. The Mexican bead lizards are bigger than Crazy monsters, with faded, black with yellow ribbons. Because it is a special predator that eats primarily eggs, the main use of the poison is still a source of debate among scientists. However, these toxins have been found to contain several enzymes that are useful for the manufacture of drugs in the treatment of diabetes, and research on the pharmacological use of the toxins is underway.
Threatened throughout its ranks due to overcollection and habitat loss, it is a CITES-protected species. The Guatemalan bead lizard ( H. Charlesbogerti ) is one of the rarest lizards in the world, with a wild population of less than 200.
Video Mexican beaded lizard
Taxonomy
The manic lizard has one close relative, the Mad Monster ( H. Suspects ), as well as many extinct relatives in Helodermatidae, whose genetic history can be traced back to the Cretaceous period. The genus of Heloderma has been present since the Miocene, when H. texana ranges in most of North America. Because helodermatids remain relatively morphologically unchanged, they are sometimes thought of as living fossils. Although beetle lizards appear to be closely related to monitor lizards (varanids) from Africa, Asia, and Australia, extensive geographic separation and unique features not found in varanids suggest that lizards are better placed in separate families.
The species was first described in 1829 by Arend Wiegmann as Trachyderma horridum , but he named it with Heloderma horridum six months later. The generic name Heloderma means "studded skin", from the Ancient Greek word hÃÆ'ªlos (????) - the head of the nail or the stud - and dÃÆ' Â © rma (?????), which means skin. Specific name, horr? Dum , is a Latin word meaning harsh or abusive.
Maps Mexican beaded lizard
Species
Four subspecies of bead lizards, increasing to full species by 2013, are:
Description
Adult bead lizards range from 57 to 91 cm (22 to 36 inches) in length. They are substantially larger than Crazy monsters, which only reach 30 to 56 centimeters (12 to 22 inches). The length of muzzle-to-vent from lizard beads averages 33 to 48 cm (13 to 19 inches). The average body mass of adult bead lizards is 800 g (1.8 lb), about 45% heavier than the average mass of crazy monsters, with large specimens exceeding 2,000 g (4.4 lb). The known maximum weight is 4,000 g (8.8 pounds) Although males are slightly larger than females, lizards are not sexually dimorphic. Both men and women are stocky with wide heads, though men tend to be wider. Small bead lizard scales, like beads, and do not overlap. Except for the bottom of the lizard, most of the scales are covered by bone osteoderms.
Their base color is black and marked with various yellow or band spots, with the exception of H. alvarezi , which tends to be black. The bead lizard has a short tail that is used to store fat so it can last for months of estivation. Unlike other lizards, these tails are not autotomized and can not grow back if damaged. The bead lizard has a pink branched tongue used for kissing, with the help of Jacobson's organs; he stuck out his tongue to collect the scent and touched it to the opening of the organ when the tongue was pulled.
Habitat and range
The beaded lizards are found in the Pacific drainage from southern Sonora to southwestern Guatemala and two Atlantic drains, from central Chiapas to southeastern Guatemala. Their habitats are mainly in deserts, tropical deciduous forests and thorn bush, but are found in pine-oak forests, with altitude from sea level up to 1500 m. In the wild, lizards are only active from April to mid November, spending about an hour per day on the ground.
Mexican bead lizard H. horridum is found in Mexico, from Sonora to Oaxaca. The Rio Fuerte bead lizard ( H. Exasperatum ) is found from southern Sonora to northern Sinaloa. The Chiapan beaded cizard ( H. Alvarezi ) is found in northern Chiapas and the depression of RÃÆ'o Lagartero in Huehuetenango to northwest of Guatemala. The range of these three species overlaps, making them sympatric. The Guatemalan bead lizard ( H. Charlesbogerti ) is the only allopatric, separated from the nearby population ( H. alvarezi ) with 250 km of unsuitable habitat. Guatemalan bead lizards are the most endangered species, if not all lizards; found only in the dry valley of RÃÆ'o Motagua in northeastern Guatemala; less than 200 are believed to be in the wild.
Ecology
Diet
Lizard beads are predators of specialized vertebrate nests, feeding primarily on birds and reptile eggs. The semi-arboreal species, found climbing tree leaves to search for prey when encountered on the ground. Sometimes prey on small birds, mammals, frogs, lizards, and insects. Steve Angeli and Robert Applegate, noting the breeders of lizard bead breeders, have said that captive specimens perform best on small vertebrate diets such as rodents and mice. Wildly captured specimens that are seized can be made to feed by using eggs on the prey item.
Venom
The toxic glands of the lizard beads are modified salivary glands located in the lower jaws of reptiles. Each gland has a separate channel leading to the base of the grooved teeth. When biting, the bead lizard hangs on the victim and chews to get his venomous saliva into the wound. Despite the tight jaw grip, the inexorable teeth were easily broken at their base. The lizard's bead poison is a weak hemotoxin, and although human deaths are rare, it can cause respiratory failure. It consists of a number of components, including the oxidase of L-amino acid, hyaluronidase, highly active phospholipase A, serotonin, and kallikreins that release vasoactive kinin. Toxins do not contain enzymes that significantly affect coagulation. Virtually all documented human bites (eight in the last century) have been generated from impulse lizard impulses with fingers or bare feet.
While invertebrates are essentially immune to the effects of these toxins, the effects on vertebrates are more severe and varied. In mammals such as mice, the main effects include rapid reduction in carotid blood flow followed by a marked decrease in blood pressure, respiratory irregularity, tachycardia, and other cardiac anomalies, as well as hypothermia, edema, and internal bleeding in the gastrointestinal tract, lung, eyes, liver, and kidney. In humans, the effects of bites are associated with extreme pain that can extend beyond the bitten area and last up to 24 hours. Other common effects of bites in humans include localized edema (swelling), weakness, sweating, and rapid drop in blood pressure. Lizard beads are immune to their own toxic effects.
Some compounds in their toxins have been shown to have pharmacological properties related to the possibility of treating diabetes, Alzheimer's disease, and even HIV. One compound, a hormone called exendin-3, is marketed by Amylin Pharmaceuticals as a drug exenatide. A study in 1996 revealed that it binds cell receptors in breast cancer cells and can stop the growth of lung cancer cells.
Reproduction
Beetle lizards mature sexually between six to eight years and couples between September and October. Men engage in frequent ritual battles of several hours; couple winners with women. The female puts a clutch of two to 30 eggs between October and December, the clutch hatches next June or July.
Young lizards are rarely seen. They are believed to spend most of their early life underground, emerging at the age of two to three years after gaining considerable size.
Preservation
Beaded lizards are surrounded by myths and superstitions in many areas of origin. Falsely believed, for example, to be more venomous than rattlesnakes, can cause a lightning strike with its tail, or make a pregnant woman miscarriage just by looking at it. As a result of this superstition, locals often kill visible lizards.
The rarely seen lizard is hunted and sold to the illegal exotic animal trade. It does not reproduce well in captivity, and its scarcity means high prices for collectors. As a direct result, the bead lizard is protected by Mexican law under category A (Threatened), and it lives within the range of some protected areas. In Guatemala, it is protected by national laws, and part of its reach is in protected areas. It is listed in Appendix II CITES.
Source of the article : Wikipedia
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