Tegu

Abstract: The tegus increase in body mass after hatching until early autumn, when the energy intake becomes gradually reduced. Resting rates of oxygen consumption in winter drop to 20% of the values in the active season ((O(2))=0.0636 ml g(-1) h(-1)) and are nearly temperature insensitive over the range of 17-25 degrees C (Q(10)=1.55). During dormancy, plasma glucose levels are 60% lower than those in active animals, while total protein, total lipids and beta-hydroxybutyrate are elevated by 24%, 43% and 113%, respectively. In addition, a significant depletion of liver carbohydrate (50%) and of fat deposited in the visceral fat bodies (24%) and in the tail (25%) and a slight loss of skeletal muscle protein (14%) were measured halfway through the inactive period. Otherwise, glycogen content is increased 4-fold in the brain and 2.3-fold in the heart of dormant lizards, declining by the onset of arousal. During early arousal, the young tegus are still anorexic, although (O(2)) is significantly greater than winter rates. The fat deposits analysed are further reduced (62% and 45%, respectively) and there is a large decrease in tail muscle protein (50%) together with a significant increase in glycogen (2-3-fold) and an increase in plasma glucose (40%), which suggests a role for gluconeogenesis as a supplementary energy source in arousing animals. No change is detectable in citrate synthase activity, but beta-hydroxyacyl CoA dehydrogenase activities are strongly affected by season, reaching a 3-fold and 5-fold increase in the liver tissue of winter and arousing animals, respectively, and becoming reduced by half in skeletal muscle and heart of winter animals compared with late fall or spring active individuals. From hatching to late autumn, the increase of the fat body mass relatively to body mass is disproportionate (b=1.44), and the mass exponent changes significantly to close to 1.0 during the fasting period. The concomitant shift in the (O(2)) mass exponent in early autumn (b=0.75) to values significantly greater than 1.0 in late autumn and during winter dormancy indicates an allometric effect on the degree of metabolic depression related to the size of the fat stores and suggests greater energy conservation in the smaller young.

Abstract: Tegu lizards have a generalist diet and may play an important role as seed dispersers in semideciduous forests in south-east Brazil. We studied the frugivory and seed dispersal of tegu lizards using captive animals and offering wild fruits from a semideciduous forest. Thirty fruit species were eaten by the lizards in captivity, ranging from 0.81 to 10.0 cm (fruit diameter). Even large fruit adapted to dispersal by large mammals were swallowed (ex. Syagrus oleracea). There were no statistical differences in seed germination between seeds that passed through the lizard gut and the control in Eugenia uniflora (c2 = 0.69, P>0.50), Genipa americana (c2 = 6.4, P>0.975), Cereus peruvianus (c2 = 0.018, P>0.10), and Solanum viarum (c2 = 6.23, P>0.975). Seed retention time in the tegu gut ranged from 2224 h (Solanum lycocarpum) to 4344 h (for Syagrus romanzoffiana). Our results indicate that tegu lizards have a potential to be an important seed dispersers in the Neotropics.

Abstract: Invasive reptilian predators can have substantial impacts on native species and ecosystems. Tegu lizards are widely distributed in South America east of the Andes, and are popular in the international live animal trade. Two species are established in Florida (U.S.A.) - Salvator merianae (Argentine black and white tegu) and Tupinambis teguixin sensu lato (gold tegu) – and a third has been recorded there— S. rufescens (red tegu). We built species distribution models (SDMs) using 5 approaches (logistic regression, multivariate adaptive regression splines, boosted regression trees, random forest, and maximum entropy) based on data from the native ranges. We then projected these models to North America to develop hypotheses for potential tegu distributions. Our results suggest that much of the southern United States and northern Mexico probably contains suitable habitat for one or more of these tegu species. Salvator rufescens had higher habitat suitability in semi-arid areas, whereas S. merianae and T. teguixin had higher habitat suitability in more mesic areas. We propose that Florida is not the only state where these taxa could become established, and that early detection and rapid response programs targeting tegu lizards in potentially suitable habitat elsewhere in North America could help prevent establishment and abate negative impacts on native ecosystems.