Tegu Lizard Research Articles

Hypoxic pulmonary vasoconstriction in reptiles: a comparative study of four species with different lung structures and pulmonary blood pressures

Low O2 levels in the lungs of birds and mammals cause constriction of the pulmonary vasculature that elevates resistance to pulmonary blood flow and increases pulmonary blood pressure. This hypoxic pulmonary vasoconstriction (HPV) diverts pulmonary blood flow from poorly ventilated and hypoxic areas of the lung to more well-ventilated parts and is considered important for the local matching of ventilation to blood perfusion. In the present study, the effects of acute hypoxia on pulmonary and systemic blood flows and pressures were measured in four species of anesthetized reptiles with diverse lung structures and heart morphologies: varanid lizards (Varanus exanthematicus), caimans (Caiman latirostris), rattlesnakes (Crotalus durissus), and tegu lizards (Tupinambis merianae). As previously shown in turtles, hypoxia causes a reversible constriction of the pulmonary vasculature in varanids and caimans, decreasing pulmonary vascular conductance by 37 and 31%, respectively. These three species possess complex multicameral lungs, and it is likely that HPV would aid to secure ventilation-perfusion homogeneity. There was no HPV in rattlesnakes, which have structurally simple lungs where local ventilation-perfusion inhomogeneities are less likely to occur. However, tegu lizards, which also have simple unicameral lungs, did exhibit HPV, decreasing pulmonary vascular conductance by 32%, albeit at a lower threshold than varanids and caimans (6.2 kPa oxygen in inspired air vs. 8.2 and 13.9 kPa, respectively). Although these observations suggest that HPV is more pronounced in species with complex lungs and functionally divided hearts, it is also clear that other components are involved.

Frugivoria e dispersão de sementes pelo lagarto teiú Tupinambis merianae (Reptilia: Teiidae)

Os lagartos teiús possuem uma dieta generalista, podendo agir como importantes dispersores de sementes em florestas semidecíduas do sudeste do Brasil. Foram estudadas a frugivoria e a dispersão de sementes de lagartos teiús usando animais em cativeiro, através da oferta de frutos de uma floresta semidecídua. Frutos de trinta espécies vegetais foram oferecidos aos lagartos em cativeiro, com diâmetro variando de 0,81 a 10,0 cm. Não foram encontradas diferenças estatísticas na germinação entre as sementes que passaram pelo trato digestivo do lagarto e as controle de Eugenia uniflora (chi²= 0.69, P>0.50), Genipa americana (chi²= 6.4, P>0.975), Cereus peruvianus (chi²= 0.018, P>0.10), e Solanum viarum (chi²= 6.23, P>0.975). O tempo de retenção da semente no tubo digestivo do teiú variou de 22 a 23 h para Solanum lycocarpum e 43 a 44 h para Syagrus romanzoffiana. Nossos resultados indicam que o lagarto teiú tem potencial para agir como um importante dispersor de sementes nos trópicos.

Structure of the posthepatic septum and its influence on visceral topology in the tegu lizard, Tupinambis merianae (Teiidae: Reptilia).

The posthepatic septum (PHS) divides the body cavity of Tupinambis merianae into two parts: the cranial one containing the lungs and liver and the caudal one containing the remaining viscera. The PHS is composed of layers of collagenous fibers and bundles of smooth muscle, neither of which show systematic orientation, as well as isolated blood vessels, lymphatic vessels, and nerves. Striated muscle of the abdominal wall does not invade the PHS. The contractions of the smooth muscles may stabilize the pleurohepatic cavity under conditions of elevated aerobic needs rather than supporting breathing on a breath-by-breath basis. Surgical removal of the PHS changes the anatomical arrangement of the viscera significantly, with stomach and intestine invading the former pleurohepatic cavity and reducing the space for the lungs. Thus, the PHS is essential to maintain the visceral topography in Tupinambis.

Reproductive and Fat Body Cycles of the Tegu Lizard, Tupinambis teguixin, in the Llanos of Venezuela

Lizards of the genus Tupinambis are large and, in places, common teiids of the tropical and subtropical regions of South America (Vanzolini, 1993). While the taxonomy of the genus is being clarified (Avila-Pires, 1995; Fitzgerald et al., 1999), aspects of their ecology, including reproductive patterns, remain largely unknown. Moreover, many thousands of individuals of two species in the genus, T teguixin and T rufescens are killed for their skins every year in southern South America (Norman, 1987; Fitzgerald, 1994a, b) making them important from a conservation viewpoint. Adult Tupinambis teguixin, often called T nigropunctatus (Avila-Pires, 1995) and known as black or common tegu lizards, weigh 1-2 kg and measure up to one m total length. They can be found in a variety of habitats in tropical South America, east of the Andes (Vanzolini, 1993). They are largely omnivorous, although animal prey, including vertebrate eggs and insect larvae, are preponderant in their diet (Herrera, 1980; Mercolli and Yanosky, 1994). Tupinambis appear to hibernate in southern South America (Gallardo, 1970) but they are active throughout the year in the

Gas exchange and ventilation during dormancy in the tegu lizard tupinambis merianae

The tegu lizard Tupinambis merianae exhibits an episodic ventilatory pattern when dormant at 17 degrees C but a uniform ventilatory pattern when dormant at 25 degrees C. At 17 degrees C, ventilatory episodes were composed of 1-22 breaths interspaced by non-ventilatory periods lasting 1.8-26 min. Dormancy at the higher body temperature was accompanied by higher rates of O(2) consumption and ventilation. The increase in ventilation was due only to increases in breathing frequency with no change observed in tidal volume. The air convection requirement for O(2) did not differ at the two body temperatures. The respiratory quotient was 0.8 at 17 degrees C and 1.0 at 25 degrees C. We found no consistent relationship between expired gas composition and the start/end of the ventilatory period during episodic breathing at 17 degrees C. However, following non-ventilatory periods of increasing duration, there was an increase in the pulmonary O(2) extraction that was not coupled to an equivalent increase in elimination of CO(2) from the lungs. None of the changes in the variables studied could alone explain the initiation/termination of episodic ventilation in the tegus, suggesting that breathing episodes are shaped by a complex interaction between many variables. The estimated oxidative cost of breathing in dormant tegus at 17 degrees C was equivalent to 52.3 % of the total metabolic rate, indicating that breathing is the most costly activity during dormancy.

Seasonal changes in blood oxygen transport in tegu lizard

Seasonal changes in blood oxygen transport in tegu lizard

The Interplay Between Life History and Environmental Stochasticity: Implications for the Management of Exploited Lizard Populations

SYNOPSIS. The sustainable use of wild species by local people is emerging as an important conservation strategy. The premise is the economic value of species will justify their own preservation as well as the habitats they occupy. However, the lack of natural history and demographic information for the majority of species being exploited or with potential uses presents challenging problems for implementing sustainable use programs. Each year in Argentina and Paraguay, an average of 1.9 million tegu lizards of the genus Tupinambis are exploited for their skins. In spite of the importance of tegus as a resource, their biology is poorly known and their populations have never been managed. The life history of Tupinambis , like that of other exploited lizards, is characterized by a relatively long life span, a large clutch size, several years of growth before reproduction, and high mortality of hatchlings. Importantly, the mortality of young-of-the-year and the proportion of females reproducing each year are both probably strongly influenced by interannual environmental variation.When these parameters were randomized in life table projections to simulate the effects of environmental stochasticity, the population growth rate was highly sensitive to environmental fluctuations. Monte Carlo simulations of different harvest strategies showed that estimates of population growth rates were overwhelmingly influenced by environmental variation and the number of years included in the growth rate estimate, even in the face of seemingly large changes in adult mortality that would result from population management. These results are both encouraging and cautionary for Tupinambis conservation. On the one hand these patterns can help explain how Tupinambis populations may have persisted in spite of high and variable harvest levels during many years, but conversely, stochastic effects make it difficult to evaluate the effects of conservation measures. Size and sex can be determined from harvested skins, and pilot studies suggest that analyses of the annual harvest can provide valuable information for evaluating long-term population trends.

Predatory behavior inTupinambis teguixin (Sauria: Teiidae). I. Tongue-flicking responses to chemical food stimuli

Black tegu lizards (Tupinambis teguixin) have the ability to detect food odors and discriminate between them and nonfood odors. This was tested by offering chemical stimuli on cotton-tipped applicators to the animals. Stimuli were from two plant and two animal species known to be principal items in these lizards' diets, demineralized water as an odorless control, and eaude-cologne as an odorous control lacking feeding or social importance. Tongueflick attack score, latency to attack, preattack tongue-flicks, and number of attacks were analyzed. The results clearly demonstrated that this species responds to chemical food stimuli, but does not respond to odorless nonfood stimuli. Responses differed among food types. There were no sex differences. These results are in agreement with the prediction that lizards having forked tongues and an active foraging mode rely on chemical cues for feeding.

A decrease in nasal CO 2 stimulates breathing in the tegu lizard

Tegu lizards decrease ventilatory frequency (f) when constant CO 2, as low as 0.4%, is delivered to the nasal cavities. In contrast, CO 2, as high as 6%, pulsed into the nasal cavities during the expiratory phase of the breathing cycle does not alter f. The purpose of the present study was to investigate further the effect of nasal CO 2 pattern on f in tegu lizards. Specifically, we tested: (1) whether f was affected by CO 2 delivered to the nasal cavities during the inspiratory phase of the breathing cycle, and (2) whether pulsed decreases in nasal CO 2 from 4% to 2% and from 4% to 0% would remove the f inhibition caused by constant nasal CO 2. Ventilation was measured using a pneumotachograph and pressure transducer in-line with an endotracheal T-tube inserted through the glottis. CO 2 was delivered to the nasal cavities through small tubes inserted into the external nares. Ventilatory frequency was not significantly altered when 4% CO 2 was pulsed into the nasal cavities during inspiration. Dropping the CO 2 in the nasal cavities from 4% to 0% at either 15 cycles/min (0.25 Hz) or for one cycle stimulated breathing. There was no significant difference between the f response to a drop in CO 2 from 4% to 0% and that to a drop in CO 2 from 4% to 2%. The failure to link the phasic CO 2 ventilatory response to a phase in the respiratory cycle indicates that the nasal CO 2 receptors do not participate in the breath-by-breath regulation of breathing in these lizards. The observation that small decreases in nasal CO 2 abolished the f inhibition caused by constant nasal CO 2 provides further evidence for the ability of the nasal CO 2 receptors to distinguish between pulsed and constant CO 2.

A telencephalospinal projection in the Tegu lizard ( Tupinambis teguixin)

Tegu lizards ( Tupinambis teguixin) were studied to determine the presence of a homologue of the mammalian corticospinal tract. The sources of telencephalic efferent projections to the spinal cord were determined by evaluating the localization of retrogradely transported horseradish peroxidase applied in the cervical spinal cord. Labeled cells were present in subtelencephalic sites reported previously by other authors and, in addition, were found in the principal sensory and motor nuclei of the trigeminal nerve and in the nucleus of the posterior commissure. A telencephalospinal projection was identified, originating in the ventral caudal telencephalon. Histochemical staining revealed a high concentration of acetylcholinesterase in cells and neuropil in the same area. This tract is suggested to be homologous to the mammalian amygdalospinal tract. No reptilian homologue of the corticospinal tract was identified.

Effect of upper airway CO2 pattern on ventilatory frequency in tegu lizards

Nasal CO2-sensitive receptors are reported to depress ventilatory frequency in several reptilian species in response to constant low levels of inspired CO2. The purpose of this study was to determine the influence of phasic patterns of CO2 in the upper airways on ventilation. Awake lizards (Tupinambis nigropunctatus) breathed through an endotracheal tube from an isolated gas source. A second gas mixture was forced at constant flow into the external nares. A concentration of 4% CO2 was intermittently pulsed through the nares in a square-wave pattern with a frequency of 60, 12, 6, 4.2, 1.8, and 0.6 cycles/min. Concentrations of 2, 3, 4, and 6% CO2 were also pulsed through the nares at 12 cycles/min and compared with sustained levels of 1, 1.5, 2, and 3%. Additionally, 0 or 3% CO2 was forced through the upper airways with a servo system designed to mimic normal ventilatory flow and gas concentrations. No changes in breathing pattern were noted during any of the pulsing protocols, although a significant breathing frequency depression was present with sustained levels of CO2 of comparable mean concentrations. We conclude that ventilatory control is selectively responsive to sustained levels of environmental CO2 but not to phasic changes in upper airway CO2 concentration.

Temperature effects on CO 2-sensitive intrapulmonary chemoreceptors in the lizard, Tupinambis nigropunctatus

Body temperature (Tb) effects on CO 2 responses of 17 intrapulmonary chemoreceptors (IPC) were investigated in 9 anesthetized (pentobarbital; 30 mg/kg) and unidirectionally ventilated tegu lizards ( Tupinambis nigropunctatus). At 30°C, all IPC (n = 15) had a stable discharge pattern. At 20°C, IPC discharge (n = 14) was stable at high P CO 2 but irregular at low P CO 2 and often ( 10 14 ) consisted of bursts of actively separated by one or more seconds of quiescence. Responses of IPC to static and dynamic changes in P CO 2 were quantified at both Tb and the discharge rate vs P CO 2 response curves were compared. Static discharge frequency (f stat) decreased as P CO 2 increased at both Tb. At 20°C: (1) f stat was diminished at all P CO 2 levels relative to 30°C; and (2) the slope of the f stat vs P CO 2 relationship was markedly attenuated. The Q 10 was 3.7 ± 0.5 and was independent of P CO 2 . The peak discharge associated with a step decrease in P CO 2 (dynamic response; f dyn) also decreased as P CO 2 increased. At 20°C: (1) f dyn was diminished at all P CO 2 levels relative to 30°C; but (2) the slope of the f dyn vs P CO 2 relationship was similar at both Tb. The Q 10 was 2.6 ± 0.3 and was significantly less than the Q 10 of f stat ( P < 0.05). Acute changes in Tb exert large effects on the CO 2 response and discharge pattern of IPC; these effects on IPC may be important in ventilatory control at different Tb in lizards.

Effect of venous (gut) CO2 loading on intrapulmonary gas fractions and ventilation in the tegu lizard.

Studies were conducted to determine regional pulmonary gas concentrations in the tegu lizard lung. Additionally, changes in pulmonary gas concentrations and ventilatory patterns caused by elevating venous levels of CO2 by gut infusion were measured. It was found that significant stratification of lung gases was present in the tegu and that dynamic fluctuations of CO2 concentration varied throughout the length of the lung. Mean FCO2 was greater and FO2 less in the posterior regions of the lung. In the posterior regions gas concentrations remained nearly constant, whereas in the anterior regions large swings were observed with each breath. In the most anterior sections of the lung near the bronchi, CO2 and O2 concentrations approached atmospheric levels during inspiration and posterior lung levels during expiration. During gut loading of CO2, the rate of rise of CO2 during the breathing pause increased. The mean level of CO2 also increased. Breathing rate and tidal volume increased to produce a doubling of VE. These results indicate that the method of introduction of CO2 into the tegu respiratory system determines the ventilatory response. If the CO2 is introduced into the venous blood a dramatic increase in ventilation is observed. If the CO2 is introduced into the inspired air a significant decrease in ventilation is produced. The changes in pulmonary CO2 environment caused by inspiratory CO2 loading are different from those caused by venous CO2 loading. We hypothesize that the differences in pulmonary CO2 environment caused by either inspiratory CO2 loading or fluctuations in venous CO2 concentration act differently on the IPC. The differing response of the IPC to the two methods of CO2 loading is the cause of the opposite ventilatory response seen during either venous or inspiratory loading.

Ventilatory Response of the Tegu Lizard to Upper Airway Hypoxia and Hyperoxia during Normocapnia or Hypercapnia

Ventilatory Response of the Tegu Lizard to Upper Airway Hypoxia and Hyperoxia during Normocapnia or Hypercapnia

Man and tegu lizards in Eastern Paraguay

Tegu lizards ( Tupinambis teguixin and Tupinambis rufescens) are found throughout Paraguay. A survey of 84 rural farmers in the country's northeastern region was carried out to assess the nature and degree of man's interaction with the lizards. The survey results show that tegus represent a significant resource to the rural peasantry. The skins provide hard currency and the meat a source of calories and protein. Sixty-seven farmaers killed approximately 850 tegus during the summer 1984–1985, with those who marketed the skins earning an average of US$ 34·92 (parallel rate) from their sale, a sum equal to 20 days of agricultural wages. Farmers of lower socio-economic strata tend to exploit greater numbers of tegu. Cultural peculiarities of non-Paraguayan immigrants affect attitudes toward exploitation. Overhunting has caused a significant reduction in tegu numbers during the past decade. Recommendations aimed at achieving a rational and sustainable harvest of these valuable species are offered.

Upper airway CO2 receptors in tegu lizards: localization and ventilatory sensitivity.

1. Tidal volume, end-tidal CO2, and ventilatory frequency in Tupinambis nigropunctatus were measured in response to CO2 (1-4%) delivered to either the mouth or nares. Additionally, the sensitivity of the ventilatory response to nasal CO2 was evaluated at CO2 concentrations less than 1%. The ventilatory parameters were also measured in response to CO2 (1-4%) delivered to the nares after the olfactory peduncle was transected. 2. It was found that (0.4-4%) nasal CO2 depressed ventilatory frequency by 9% to 83% respectively, while tidal volume was not significantly altered. CO2 (1-4%) delivered to the mouth produced no apparent changes in any of the ventilatory parameters. Following transection of the olfactory peduncle, nasal CO2 was ineffective in producing any change in ventilatory frequency or depth. 3. These findings indicate that CO2-sensitive receptors are located in either the nasal or vomeronasal membranes of tegu lizards and that the olfactory peduncle must be intact for these receptors to affect ventilatory changes in response to elevated CO2 concentrations. The receptors are capable of mediating a ventilatory response to CO2 concentrations lower than those found in either expired air or in confined spaces such as occupied burrows. 4. The discrepancies in the ventilatory responses of lizards and snakes to inspired CO2 reported in past experiments may be partially explained by the presence of nasal or vomeronasal CO2-sensitive receptors.

The Effects of Hypercapnia on the Arterial Acid-Base Status in the Tegu Lizard, Tupinambis Nigropunctatus

ABSTRACT The effects of hypercapnia on the arterial acid-base status of the Tegu lizard, Tupinambis nigropunctatus (Spix), were studied at 25 °C. Arterial increased over the first 2 h of hypercapnia causing a fall in arterial plasma pH (pHa) of about 0·17 units with ≈4% CO2 and about 0·3 units with ≈7 % CO2. In both conditions, plasma pH increased slightly (≈ 0·02 units) between 2 and 72 h. Plasma [HCO3−] rose during the initial increase of (by approx. 5·5 mmol l−1 with ≈7 % CO2; approx. 1·9 mmol l−1 with ≈4% CO2) during the first 2h, and further increased by 4 mmol I-1 between 2 and 72 h of hypercapnia, while did not change. The increases of plasma [HCO3−] resulted in a recovery of pH, by 38 or 32 % (≈4 and ≈7 % CO2, respectively) relative to the fall of pHa that would occur at constant [HCO3−]. The limited and incomplete compensation of pHa during environmental hypercapnia is consistent with data for other air-breathing ectothermic vertebrates, and contrasts with the typical response of water-breathing fish, in which compensation is usually complete.

Breathing response of the tegu lizard to 1–4% CO 2 in the mouth and nose or inspired into the lungs

This study investigated the influence on ventilation of elevated CO 2 in the nasal and buccal cavities (NaBuCO 2) vs the effect of elevated CO 2 levels inspired into the lungs (LuCO 2). Separate gas sources were used to independent alter NaBuCo 2 and LuCo 2. As little as 1% NaBuCO 2 or LuCO 2 significantly increased the pause duration between the active expiratory-inspiratory cycles. Elevated NaBuCO 2 caused minor changes in tidal volume, mean inspiratory and expiratory flow, and inspiratory and expiratory durations with a significant reduction in total ventilation. Elevated LuCO 2 had little effect on inspiratory or expiratory durations but unlike CO 2 in the upper airways, significantly increased tidal volume and mean inspiratory and expiratory flows. This study demonstrates that the increased pause duration seen in the tegu lizard to elevated environmental CO 2 is due to a receptor response in the buccal or nasal cavities and also to elevated CO 2 concetrations inpired into the lungs. Sensitivity of the ventilatory response to CO 2 in the upper airways is well within a physiologically relevant range.

Alpha-Crystallin A sequences of Alligator mississippiensis and the lizard Tupinambis teguixin: molecular evolution and reptilian phylogeny.

The amino acid sequences of the eye lens protein alpha-crystallin A from many mammalian and avian species, two frog species, and a dogfish have provided detailed information about the molecular evolution of this protein and allowed some useful inferences about phylogenetic relationships among these species. We now have isolated and sequenced the alpha-crystallins of the American alligator and the common tegu lizard. The reptilian alpha A chains appear to have evolved as slowly as those of other vertebrates, i.e., at two to three amino acid replacements per 100 residues in 100 Myr. The lack of charged replacements and the general types and distribution of replacements also are similar to those in other vertebrate alpha A chains. Maximum-parsimony analyses of the total data set of 67 vertebrate alpha A sequences support the monophyletic origin of alligator, tegu, and birds and favor the grouping of crocodilians and birds as surviving sister groups in the subclass Archosauria.

The matching of ventilation and perfusion in the lung of the Tegu lizard, Tupinambis nigropunctatus

Ventilation-perfusion (V̇ A/Q̇) distribution was evaluated in the Tegu lizard, Tupinambis nigropunctatus, using the multiple inert gas elimination technique (MIGET) in order to define the limitations to gas exchange in the large chambered unicameral lung. The lizards (0.52–1.1 kg) were anesthetized with halothane and ventilated. Body temperature was maintained at 35°C. Arterial and sinus venosus P O 2 averaged 79.4 ± 5.9 and 47.3 ± 6.4 torr while breathing air and 232.1 ± 31 and 64.8 ± 11.5 torr while breathing oxygen. V̇ A/Q̇ distributions were broad and right-to-left shunt averaged 21% while breathing air and 27% while breathing oxygen. Gas exchange was significantly impaired due to the presence of both shunt and V̇ A/Q̇ heterogeneity. The walls of the lung enclose a large axial air chamber. Microscopic examination revealed approximately three generations of septa which subdivided the wall into tubular-shaped gas-exchange chambers. Wall thickness averages 2.8 mm at the anterior end of the lung, 2.1 mm in the middle portion of the lung and 1.4 mm at the posterior end. The thickness of the blood-air barrier (epithial-basal lamina-endothelial cell layer) ranged from 0.35 to 0.90 μm. Although this barrier is slightly thicker than in the mammalian lung (0.1–0.5 μm), it is unlikely to be a source of diffusion limitation in gas exchange at rest.