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Spiny-Tailed Iguana (Ctenosaura similis)



Spiny-Tailed Iguana (Ctenosaura similis)
Order: Squamata, Family: Iguanidae

The spiny-tailed iguana is found throughout Mexico, large areas in Central America and islands adjacent to Panama. Spiny-tailed iguanas are large, bulky lizards with adult males reaching up to 18 inches long with an 18-inch tail.



I. GEOGRAPHIC RANGE
  • The spiny-tailed iguana is found throughout Mexico, large areas in Central America and islands adjacent to Panama.
II. PHYSICAL CHARACTERISTICS
  • Mass: 1 kg, on average.
  • Spiny-tailed iguanas are large, bulky lizards with adult males reaching up to 18 inches long with an 18-inch tail.
  • They are predominantly black but the dorsal surface may show black bands on a grayish background. Most have black mottling on their backs. The color may also lighten after basking in the sunlight with yellowish and orange markings becoming evident along the sides. Juveniles tend to be olive-green becoming tan and then finally grayish as they grow.
  • Adult males and females are dimorphic. Adult males have well developed dorsal crests and small dewlaps. The dewlap, the crescent of skin that can be extended under the throat, is not inflated. A small bone bows out to extend the dewlap during times of threat, courtship, or while defending territory. Females lack obvious crests. There is considerable variation with age and sex and therefore identification may be difficult.
  • The lizards have tails ringed with rows of sharp, curved spines, hence the name spiny-tailed iguana. The spines down the back are short.
III. FOOD HABITS
  • Spiny-tailed iguanas are generally herbivorous. They prefer legume fruits, but are also known to have a diverse carnivorous diet that consists of small animals. They are known to eat rodents, bats, frogs, small birds and a variety of insects. They have even been noted to eat eggs of their own young, and in one case, the tail of a juvenile was found inside an adult male, suggesting cannibalism. Youngsters are primarily insectivorous, switching into herbivorous habits as adults.
IV. REPRODUCTION
  • This species becomes sexually mature at around 3 or 4 years of age. They congregate and mate during specific times of year that varies between populations.
  • Male iguanas possess a pair of copulatory organs, the hemipenes. When not in use the hemipenes lie adjacent to the cloaca within the base of the tail. During sexual activity one hemipenis is turned inside out by the action of muscles and fills with blood. In copulation, which follows courtship behavior, only a single hemipenis is inserted into the female's cloaca, and the sperm travel along a groove in the hemipenis. Retraction of the hemipenis is accomplished by drainage of the blood sinuses and activation of retractor muscles that invert the structure as it is withdrawn.
  • In breeding season, the oviparous females then migrate to suitable areas to nest. After digging a burrow about half a meter deep, the female lays 2 to 25 eggs in the nest. She then defends the burrow for some time to prevent other females from nesting in the same spot.
  • The young iguanas hatch 3 to 4 months later and then take about a week to dig their way out of the nest. These tiny iguanas can easily fit in the palm of a hand. If they survive the first difficult years of life, when food is often scarce and predators such as hawks and owls are dangers, these iguanas can live more than 60 years.
V. BEHAVIOR
  • This species can be belligerent, and may bite or wound an aggressor with their spines.
  • More terrestrial than arboreal, they can run in a bipedal fashion.
  • Highly gregarious and territorial, these iguanas live in colonies, ruled by a strict pecking order. One male in the colony is dominant, and although the other males hold territories, they will only defend them against one another and not against the leader. Territorial displays involve color changes, body inflation, jaw gaping, "push-ups" or rapid nodding of the head, and sometimes, biting and tail thrashing battles. Larger males usually hold bigger and better territories and they mate more often. Combat often occurs when iguanas are attaining or defending a territory or a mate.
  • The male always courts, but he can only progress if his partner provides him with the right stimuli. She must respond by sexual stimuli, and like one of his own species; with a female of the wrong species his reproductive investments would result in sterile hybrids, if any offspring at all. She must also signal that she is receptive with mature ova ready for fertilization. During courtship the males often bite, scratch or lick females that have signaled their receptivity.
  • Juvenile iguanas often emerge together from the nest hole, an anti-predator strategy in which many eyes are better than two and large numbers make individual capture less likely. Young iguanas often remain in groups with one of them temporarily behave as the leader. They engage in mutual tongue licking and grooming, body and chin rubbing. At night they often sleep together on branches.
VI. HABITAT
  • These lizards are found around ruins, stonewalls, rocky open slopes and branches of large trees along the open borders of the forests. They generally live in dry, arid, open terrain.
VII. ECONOMIC IMPORTANCE FOR HUMANS
  • Positive
    The spiny-tailed iguana is edible and is a popular food for much of the rural population of Central America. In some areas, eating their flesh is considered potent "medicine", with the person deriving the iguana's strength after eating it. Also, the spiny-tailed iguanas are supposed to be a cure for impotence.
  • Negative
    No documented example.
      VIII. CONSERVATION
      • Man and his domestic animals are inevitably destroying the iguanas' environments and their species. Domestic animals such as cows devour most of the vegetation, which are the food sources for the iguanas.
      • Their flesh is relished in many parts of the world but it is not overly exploited.
      • In parts of South America, men imitating the screams of hawks hunt iguanas. The iguanas' reaction to the cries is to "freeze" and they are then easily caught.



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