The Argentine black and white tegu (Salvator merianae), also commonly known as the Argentine giant tegu, the black and white tegu, the blue tegu, and the huge tegu, is a species of lizard in the family Teiidae. The species is the largest of the "tegu" lizards. It is an omnivorous species, which inhabits the tropical rain forests, savannas, and semideserts of eastern and central South America. It is native to south and southeastern Brazil, Uruguay, eastern Paraguay, Bolivia, and Argentina.
Tegu lizards are sometimes kept as pets, being notable for their unusually high intelligence and their relatively gentle nature. Like some reptiles, tegus enter brumation in autumn when ambient temperature drops. They exhibit a high level of activity during their wakeful period of the year. They are the only known nonavian reptiles to be partly endothermic during breeding season.
Tegus fill ecological niches similar to those of monitor lizards, but are only distantly related to them; the similarities are an example of convergent evolution.
Taxonomy and etymology
The Argentine black and white tegu is a member of the family Teiidae, which also includes racerunners and whiptails. The term "tegu" refers to 9 genera within Teiidae (though new taxonomic classifications change), with the Argentine black and white tegu being assigned to the genus Salvator.
In 1839, this species of tegu was originally described as Salvator merianae. However, beginning in 1845 and continuing for 154 years, it was confused with Tupinambis teguixin and was considered a synonym of that species. In 1995, it was again given species status, as Tupinambis merianae because subsequent studies had shown that the gold tegu (Tupinambis teguixin) was distinct from it. In 2012, the Argentine black and white tegu was reassigned to the resurrected genus Salvator as Salvator merianae.
The genus Salvator can be distinguished from Tupinambis by the presence of two loreal scales between the eye and the nostril, as opposed to only one.
Etymology The specific name, merianae, is in honor of German-born naturalist Maria Sibylla Merian, xiii + 296 pp. (Tupinambis merianae, p. 175). a naturalist and artist who studied insects, plants, and reptiles from the 17th to the 18th centuries.
S. merianae is called the "Argentine black and white tegu" to distinguish it from the "Colombian black and white tegu", which is another name for the gold tegu. Unscrupulous or incompetent pet dealers sometimes pass off gold tegus as Argentine black and white tegus.
Hybridization In the ecotone between the arid Chaco and the Espinal of central Argentina, they are known to naturally hybridise with the red tegu (Salvator rufescens) with a stable hybrid zone.
Distribution and habitat
As one of its common names would suggest, Salvator merianae is native to Argentina, but also to Brazil, Paraguay, Bolivia, and Uruguay.
Significant populations of Argentine black and white tegus occur in the southern United States and the Brazilian coast. They are a consistently problematic invasive species in Florida and Georgia, along with sightings in South Carolina, most likely as a result of escaped or released specimens from the early-2000s pet trade. Previous studies have found that the differing weather and climate patterns far outside of their natural habitat range do not prevent adult Argentine black and white tegus from surviving in diverse areas across the United States, furthering concerns about their invasive status. In the wild, tegus inhabit both forested and open-plain environments, widening their potential invasive range. The first evidence of a reproducing population of these tegus into southeastern Florida occurred when a female was tracked to her nest mound. One clutch of 21 eggs from the current year was found and one clutch of 22 hatched eggshells and 13 unhatched eggs was found from a past year. Established communities were identified in Hillsborough and Polk Counties in Florida.
Tegus have also been found in scrub and wet habitats such as flooded savannas, canals, ponds, and streams. They largely seem to not discriminate in habitat type as long as they have the ability to burrow.
Description As a hatchling, Salvator merianae has an emerald-green color from the tip of its snout to midway down its neck, with black markings. The emerald green becomes black several months after shedding. As a young tegu, the tail is banded yellow and black; as it ages, the solid yellow bands nearest to the body change to areas of weak speckling. Fewer solid bands indicate an older animal. A tegu can drop a section of its tail as a distraction if attacked. The tail is also used as a weapon to swipe at an aggressor or potential predator. Capable of living 12 to 15 years in the wild, tegus could survive more than 20 years in captivity with excellent care.
The skull is heavily built with a large facial process of the maxilla, a single premaxilla, paired nasals, a single frontal bone, and two parietal bones separated by the sagittal suture. Biomechanical analyses suggest the posterior processes of the parietal might be important for dealing with torsional loads due to posterior biting on one side. In the large adults, the posterior teeth are larger and more rounded than the anterior teeth.
Sexual dimorphism
Adult males, much larger than the females, can exceed in total length (tail included) at maturity. They may continue to grow to total lengths of .
The females are smaller, but may grow up to in length from nose to tail tip. Adult females can reach a weight of . (in Spanish, with an abstract in English).
When a tegu reaches the age of 8 months, its gender can easily be determined visually. The vent at the base of the tail bulges if it is a male, but lies flat if it is a female. In adults, the main difference is in the jowls. Males have substantially developed jowls as a result of hypertrophic lateral pterygoideus muscles. Females' jawlines are more streamlined.
Ecology
Diet
Tegus are omnivorous; juveniles in the wild have been observed to eat a wide range of vertebrates, invertebrates, fruits, and seeds. A non-exhaustive list includes insects, annelids, crustaceans, in spiders, snails, small birds, fish, frogs, other lizards, snakes rodents, armadillos, bananas, grapes, mangoes, and papayas.
Tegus are notorious egg predators, seeking out eggs from the nests of birds and other reptiles. This makes them a concerning predator of sea turtles, alligators, and crocodiles as their invasive populations spread across the United States.
As adults, their plant consumption increases, but their diet varies by season, with small vertebrate prey being more common in the spring, while plants and invertebrates are more commonly consumed in the summer.
In captivity, tegus commonly are fed high-protein diets that include raw or cooked flesh, such as ground turkey, canned or dry dog food, commercial crocodile diet, chicken, eggs, insects, and small rodents. They are also fed various feeder insects, such as mealworms, superworms, earthworms, silkworms, crickets, and cockroaches. Some evidence indicates that cooking most of the egg in the diet is a good practice, so as to denature the protein avidin that occurs in the albumen. Raw avidin immobilises biotin, so excessive feeding of raw eggs may cause fatal biotin deficiency.
Like all lizards, these tegus need a properly balanced diet and the inclusion of fruit in the diet is recommended. Incomplete prey items such as insects or ground meat require dusting with a mineral/multivitamin supplement. Vitamin deficiencies can lead to trouble shedding skin, lethargy, and weight loss; a calcium deficiency can lead to metabolic bone disease, which can be fatal.
Mortality Predators of tegus include cougars, jaguars, otters, snakes, caimans, and birds of prey. A known predator of the Argentine black and white tegu is the lesser grison (Galictis cuja), a mustelid related to weasels. Salmonella enterica was found in fecal samples from almost all S. merianae at a captive-breeding field station at State University of Santa Cruz, Ilhéus, Bahia, Brazil, illustrating the prevalence of Salmonella infection in tegus. Roads and vehicles pose a threat; it is one of the most frequently road-killed reptile species in its native range.
Life cycle
Eggs of the Argentine black and white tegu usually hatch at the beginning of spring. Each hatchling weighs about and grows to within four or five years, experiencing a nearly 800-fold increase in body size. During this time, its diet changes from insects to small vertebrates, eggs, carrion, and fruits. It is reproductively mature by its third year, when it weighs around , and ceases growing by around its fourth year, with the highest growth rate being its first and second years of life. S. merianae also experiences a seasonal lifecycle that begins within its first year, being very active during hotter months and in a brumation state in the colder months. Regardless of the season, the Argentine tegu does not experience any significant fluctuations in metabolism or body mass, which means its sensitivity to temperature underlying its metabolic rate does not change body mass. This differs from other endotherms and further explains the tegu's alternating endothermic and ectothermic behavior.
Brain vesicles (constructed from two neural tube constrictions) that make up the anterior forebrain, midbrain, and posterior hindbrain are developed and distinguishable from day three of embryonic development. On day four, visceral arches (consisting of mesenchymal tissue condensation and separated by grooves) form and are fully grown and fused by day nine. Day four also marks the development of limbs as small swellings. Its hindlimb development (developing claws faster than the forelimb) is more similar to crocodile or turtle embryonic development than other lizards. This alludes to the hindlimbs having greater functionality in tegu adults. Pigmentation is the last morphological structure to form and occurs late in development after other distinguishing characteristics have already been formed (such as scales). Pigmentation is observed from day 39 first on the dorsal portion of the head and body. It later extends down to the proximal and distal portions of the limbs by day 45 and extends down to the flanks by day 48. As development advances, the pattern begins to show lateral stretch marks by day 51. Pigmentation of the ventral portion of the body occurs between days 57 and 60, characterized by individualized spot patterns. Paired genital tubercles manifest in both sexes (called hemipenes in males). Reptile embryo development involves separate processes of differentiation and embryo growth. Differentiation is determined by external morphological features and is documented early. As the embryo approaches hatching, development stages are categorized into periods rather than ages (characterized by parameters of development speed).
Behavior Aggression