Effects of different levels of hypoxia and hypercarbia on ventilation and gas exchange in Boa constrictor amaralis and Crotalus durissus (Squamata: Serpentes)

Ventilation and gas exchange have been studied in relatively few species of snakes, especially regarding their response to environmental hypoxia or hypercarbia. We exposed Crotalus durissus (N = 6) and Boa constrictor (N = 6) to decreasing levels of oxygen (12, 9, 6, 3 % O₂) and increasing levels of carbon dioxide (1.5, 3.0, 4.5, 6.0 % CO₂) and analyzed the effect of the different gas mixtures on ventilation and gas exchange using open-flow respirometry. Neither hypoxia nor hypercarbia significantly altered the duration of expiration or inspiration, nor their proportions. Both hypoxia and hypercarbia increased minute ventilation, but the decrease in oxygen had a less pronounced effect on ventilation. Gas exchange under normoxic conditions was low and was not significantly affected by hypoxia, but hypercarbia decreased gas exchange significantly in both species. While B. constrictor maintained its respiratory exchange ratio (RER) under hypercarbia between 0.5 and 1.0, C. durissus showed a RER above 1.0 during hypercarbia, due to a significantly greater CO₂ excretion. The overall responses of both species to hypercarbia and especially to hypoxia were very similar, which could be associated to similar lifestyles as ambush hunting sit-and-wait predators that are able to ingest large prey items. The observed differences in gas exchange could be related to respiratory systems with macroscopically different structures, possessing only a tracheal lung in C. durissus, but two functional lungs in B. constrictor.

Autonomic control of cardiovascular adjustments associated with orthostasis in the scansorial snake Boa constrictor

Orthostatic hypotension is a phenomenon triggered by a change in the position or posture of an animal, from a horizontal to a vertical head-up orientation, characterised by a blood pooling in the lower body and a reduction in central and cranial arterial blood pressure (P _A). This hypotension elicits systemic vasoconstriction and tachycardia, which generally reduce blood pooling and increase P _A Little is known about the mediation and importance of such cardiovascular adjustments that counteract the haemodynamic effects of orthostasis in ectothermic vertebrates, and some discrepancies exist in the information available on this subject. Thus, we sought to expand our knowledge on this issue by investigating it in a more elaborate way, through an in vivo pharmacological approach considering temporal circulatory changes during head-up body inclinations in unanaesthetised Boa constrictor To do so, we analysed temporal changes in P _A, heart rate (f _H) and cardiac autonomic tone associated with 30 and 60 deg inclinations, before and after muscarinic blockade with atropine, double blockade with atropine and propranolol, and α₁-adrenergic receptor blockade with prazosin. Additionally, the animals' f _H variability was analysed. The results revealed that, in B. constrictor: (1) the orthostatic tachycardia is initially mediated by a decrease in cholinergic tone followed by an increase in adrenergic tone, a pattern that may be evolutionarily conserved in vertebrates; (2) the orthostatic tachycardia is important for avoiding an intense decrease in P _A at the beginning of body inclinations; and (3) α₁-adrenergic orthostatic vasomotor responses are important for the maintenance of P _A at satisfactory values during long-term inclinations.

The autonomic control of upright posture tachycardia in the arboreal lizard Iguana iguana

In terrestrial environments, upright spatial orientation can dramatically influence animals' hemodynamics. Generally, large and elongated species are particularly sensitive to such influence due to the greater extent of their vascular beds being verticalized, favoring the establishment of blood columns in their bodies along with caudal blood pooling, and thus jeopardizing blood circulation through a cascade effect of reductions in venous return, cardiac filling, stroke volume, cardiac output, and arterial blood pressure. This hypotension triggers an orthostatic-(baroreflex)-tachycardia to normalize arterial pressure, and despite the extensive observation of this heart rate (fH ) adjustment in experiments on orthostasis, little is known about its mediation and importance in ectothermic vertebrates. In addition, most of the knowledge on this subject comes from studies on snakes. Thus, our objective was to expand the knowledge on this issue by investigating it in an arboreal lizard (Iguana iguana). To do so, we analyzed fH , cardiac autonomic tones, and fH variability in horizontalized and tilted iguanas (0°, 30°. and 60°) before and after muscarinic blockade with atropine and double autonomic blockade with atropine and propranolol. The results revealed that I. Iguana exhibits significant orthostatic-tachycardia only at 60o inclinations-a condition that is primarily elicited by a withdrawal of vagal drive. Also, as in humans, increases in low-frequency fH oscillations and decreases in high-frequency fH oscillations were observed along with orthostatic-tachycardia, suggesting that the mediation of this fH adjustment may be evolutionarily conserved in vertebrates.

Beyond body size: muscle biochemistry and body shape explain ontogenetic variation of anti-predatory behaviour in the lizard Salvator merianae

Anti-predatory behaviour evolves under the strong action of natural selection because the success of individuals avoiding predation essentially defines their fitness. Choice of anti-predatory strategies is defined by prey characteristics as well as environmental temperature. An additional dimension often relegated in this multilevel equation is the ontogenetic component. In the tegu Salvator merianae, adults run away from predators at high temperatures but prefer fighting when it is cold, whereas juveniles exhibit the same flight strategy within a wide thermal range. Here, we integrate physiology and morphology to understand ontogenetic variation in the temperature-dependent shift of anti-predatory behaviour in these lizards. We compiled data for body shape and size, and quantified enzyme activity in hindlimb and head muscles, testing the hypothesis that morphophysiological models explain ontogenetic variation in behavioural associations. Our prediction is that juveniles exhibit body shape and muscle biochemistry that enhance flight strategies. We identified biochemical differences between muscles mainly in the LDH:CS ratio, whereby hindlimb muscles were more glycolytic than the jaw musculature. Juveniles, which often use evasive strategies to avoid predation, have more glycolytic hindlimb muscles and are much smaller when compared with adults 1-2 years old. Ontogenetic differences in body shape were identified but marginally contributed to behavioural variation between juvenile and adult tegus, and variation in anti-predatory behaviour in these lizards resides mainly in associations between body size and muscle biochemistry. Our results are discussed in the ecological context of predator avoidance by individuals differing in body size living at temperature-variable environments, where restrictions imposed by the cold could be compensated by specific phenotypes.

Hábitos alimentares de serpentes em Espigão do Oeste, Rondônia, Brasil

O presente estudo teve como objetivo estudar os hábitos alimentares das serpentes em Espigão do Oeste, Rondônia (Sudoeste da Amazônia), Brasil. As serpentes foram registradas através de procura limitada por tempo, armadilhas de interceptação e queda, coleta por terceiros e encontros ocasionais. As serpentes coletadas tiveram o conteúdo estomacal e intestinal examinados. Em 89 espécimes pertencentes a 31 espécies de serpentes foram registradas informações sobre alimentação. Dos 114 itens registrados (conteúdos estomacais e observações na natureza), a maioria foi de anuros (38%), seguidos de mamíferos (16%), lagartos (15%), moluscos (13%), aves (5%) e serpentes (5%). A maioria das espécies de serpentes de Espigão do Oeste preda lagartos, assim como na Amazônia Central (Manaus). Uma menor proporção de serpentes na Amazônia utiliza anuros em relação às regiões do Pantanal, sul e sudeste do Brasil. Essas diferenças podem ser devidas à maior proporção de Xenodontinae nas comunidades extra-amazônicas, uma vez que muitas das serpentes desse clado predam anuros. A maioria dos anfíbios anuros e lagartos encontrados nos conteúdos estomacais das serpentes apresentam hábitos terrícolas, o que deve estar associado com a maioria das espécies de serpentes (52%) forragearem sobre o chão.

Lagartos (Squamata: Lacertilia) em áreas de floresta e de pastagem em Espigão do Oeste, Rondônia, sudoeste da Amazônia, Brasil

O presente estudo apresenta dados sobre riqueza e freqüência de captura de lagartos em áreas de floresta e pastagem em uma localidade em Rondônia (sudoeste da Amazônia) utilizando três métodos de amostragem: armadilhas de interceptação e queda, procura noturna limitada por tempo (encontro de espécimes dormindo sobre a vegetação) e encontros ocasionais. Foram encontradas 29 espécies distribuídas em nove famílias. A maioria das espécies (28) foi encontrada em floresta, enquanto que na pastagem foram encontradas oito. A maioria das espécies foi registrada pelas armadilhas de interceptação e queda (22), seguido pelos encontros ocasionais (16) e procura noturna (9). A curva do coletor apresentando dados de todos os métodos mostra que a partir do oitavo mês de amostragem não houve mais nenhum acréscimo de nova espécie nessa comunidade, evidenciando que a mesma foi bem amostrada. O fato de algumas espécies terem sido coletadas exclusivamente em apenas um dos métodos, demonstra a importância de se usar dois ou mais métodos de amostragem em estudos sobre comunidades. Essa redução de espécies se deve a retirada da cobertura vegetal e, possivelmente, às suas conseqüências: aumento das taxa de predação e de competição, dificuldades para a termo-regulação, perda de locais para abrigos e reprodução, diminuição dos recursos alimentares e perda de serapilheira.

Physiological and morphological responses to feeding in broad-nosed caiman (Caiman latirostris)

Broad nosed caiman are ectotherm sauropsids that naturally experience long fasting intervals. We have studied the postprandial responses by measuring oxygen consumption using respirometry, the size changes of the duodenum, the distal small intestine, and the liver, using repeated non-invasive ultrasonography, and by investigating structural changes on the level of tissues and cells by using light- and electron microscopy. The caimans showed the same rapid and reversible changes of organ size and identical histological features, down to the ultrastructure level, as previously described for other ectothermic sauropsids. We found a configuration change of the mucosa epithelium from pseudostratified during fasting to single layered during digestion, in association with hypertrophy of enterocytes by loading them with lipid droplets. Similar patterns were also found for the hepatocytes of the liver. By placing the results of our study in comparative relationship and by utilizing the phylogenetic bracket of crocodiles, birds and squamates, we suggest that the observed features are plesiomorphic characters of sauropsids. By extending the comparison to anurans, we suggest that morphological and physiological adjustments to feeding and fasting described here may have been a character of early tetrapods. In conclusion, we suggest that the ability to tolerate long fasting intervals and then swallow a single large meal as described for many sit-an-wait foraging sauropsids is a functional feature that was already present in ancestral tetrapods.

Diet, phylogeny, and basal metabolic rate in phyllostomid bats

Aside from the pervasive effects of body mass, much controversy exists as to what factors account for interspecific variation in basal metabolic rates (BMR) of mammals; however, both diet and phylogeny have been strongly implicated. We examined variation in BMR within the New World bat family Phyllostomidae, which shows the largest diversity of food habits among mammalian families, including frugivorous, nectarivorous, insectivorous, carnivorous and blood-eating species. For 27 species, diet was taken from the literature and BMR was either measured on animals captured in Brazil or extracted from the literature. Conventional (nonphylogenetic) analysis of covariance (ANCOVA), with body mass as the covariate, was first used to test the effects of diet on BMR. In this analysis, which assumes that all species evolved simultaneously from a single ancestor (i.e., a "star" phylogeny), diet exerted a strong effect on mass-independent BMR: nectarivorous bats showed higher mass-independent BMR than other bats feeding on fruits, insects or blood. In phylogenetic ANCOVAs via Monte Carlo computer simulation, which assume that species are part of a branching hierarchical phylogeny, no statistically significant effect of diet on BMR was observed. Hence, results of the nonphylogenetic analysis were misleading because the critical values for testing the effect of diet were underestimated. However, in this sample of bats, diet is perfectly confounded with phylogeny, because the four dietary categories represent four separate subclades, which greatly reduces statistical power to detect a diet (= subclade) effect. But even if diet did appear to exert an influence on BMR in this sample of bats, it would not be logically possible to separate this effect from the possibility that the dietary categories differ for some other reason (i.e., another synapomorphy of one or more of the subclades). Examples such as this highlight the importance of considering phylogenetic relationships when designing new comparative studies, as well as when analyzing existing data sets. We also discuss some possible reasons why BMR may not coadapt with diet.

The ventilatory response to environmental hypercarbia in the South American rattlesnake, Crotalus durissus

To study the effects of environmental hypercarbia on ventilation in snakes, particularly the anomalous hyperpnea that is seen when CO(2) is removed from inspired gas mixtures (post-hypercapnic hyperpnea), gas mixtures of varying concentrations of CO(2) were administered to South American rattlesnakes, Crotalus durissus, breathing through an intact respiratory system or via a tracheal cannula by-passing the upper airways. Exposure to environmental hypercarbia at increasing levels, up to 7% CO(2), produced a progressive decrease in breathing frequency and increase in tidal volume. The net result was that total ventilation increased modestly, up to 5% CO(2) and then declined slightly on 7% CO(2). On return to breathing air there was an immediate but transient increase in breathing frequency and a further increase in tidal volume that produced a marked overshoot in ventilation. The magnitude of this post-hypercapnic hyperpnea was proportional to the level of previously inspired CO(2). Administration of CO(2) to the lungs alone produced effects that were identical to administration to both lungs and upper airways and this effect was removed by vagotomy. Administration of CO(2) to the upper airways alone was without effect. Systemic injection of boluses of CO(2)-rich blood produced an immediate increase in both breathing frequency and tidal volume. These data indicate that the post-hypercapnic hyperpnea resulted from the removal of inhibitory inputs from pulmonary receptors and suggest that while the ventilatory response to environmental hypercarbia in this species is a result of conflicting inputs from different receptor groups, this does not include input from upper airway receptors.

Autonomic control of heart rate during forced activity and digestion in the snakeBoa constrictor

Reptiles, particularly snakes, exhibit large and quantitatively similar increments in metabolic rate during muscular exercise and following a meal, when they are apparently inactive. The cardiovascular responses are similar during these two states, but the underlying autonomic control of the heart remains unknown. We describe both adrenergic and cholinergic tonus on the heart during rest, during enforced activity and during digestion (24–36 h after ingestion of 30 % of their body mass) in the snake Boa constrictor. The snakes were equipped with an arterial catheter for measurements of blood pressure and heart rate, and autonomic tonus was determined following infusion of the β-adrenergic antagonist propranolol (3 mg kg–1) and the muscarinic cholinoceptor antagonist atropine (3 mg kg–1).

The mean heart rate of fasting animals at rest was 26.4±1.4 min–1, and this increased to 36.1±1.4 min–1 (means ± s.e.m.; N=8) following double autonomic block (atropine and propranolol). The calculated cholinergic and adrenergic tones were 60.1±9.3 % and 19.8±2.2 %, respectively. Heart rate increased to 61.4±1.5 min–1 during enforced activity, and this response was significantly reduced by propranolol (maximum values of 35.8±1.6 min–1), but unaffected by atropine. The cholinergic and adrenergic tones were 2.6±2.2 and 41.3±1.9 % during activity, respectively. Double autonomic block virtually abolished tachycardia associated with enforced activity (heart rate increased significantly from 36.1±1.4 to 37.6±1.3 min–1), indicating that non-adrenergic, non-cholinergic effectors are not involved in regulating heart rate during activity. Blood pressure also increased during activity.

Digestion was accompanied by an increase in heart rate from 25.6±1.3 to 47.7±2.2 min–1 (N=8). In these animals, heart rate decreased to 44.2±2.7 min–1 following propranolol infusion and increased to 53.9±1.8 min–1 after infusion of atropine, resulting in small cholinergic and adrenergic tones (6.0±3.5 and 11.1±1.1 %, respectively). The heart rate of digesting snakes was 47.0±1.0 min–1 after double autonomic blockade, which is significantly higher than the value of 36.1±1.4 min–1 in double-blocked fasting animals at rest. Therefore, it appears that some other factor exerts a positive chronotropic effect during digestion, and we propose that this factor may be a circulating regulatory peptide, possibly liberated from the gastrointestinal system in response to the presence of food.

Energetic and physiological correlates of prey handling and ingestion in lizards and snakes

In this review, we summarize the energetic and physiological correlates of prey handling and ingestion in lizards and snakes. There were marked differences in the magnitude of aerobic metabolism during prey handling and ingestion between these two groups, although they show a similar pattern of variation as a function of relative prey mass. For lizards, the magnitude of aerobic metabolism during prey handling and ingestion also varied as a function of morphological specializations for a particular habitat, prey type, and behavior. For snakes, interspecific differences in aerobic metabolism during prey handling seem to be correlated with adaptations for prey capture (venom injection vs. constriction). During ingestion by snakes, differences in aerobic metabolism might be due to differences in cranial morphology, although allometric effects might be a potentially confounded effect. Anaerobic metabolism is used for prey handling and ingestion, but its relative contribution to total ATP production seems to be more pronounced in snakes than in lizards. The energetic costs of prey handling and ingestion are trivial for both groups and cannot be used to predict patterns of prey-size selection. For lizards, it seems that morphological and ecological factors set the constraints on prey handling and ingestion. For snakes, besides these two factors, the capacity of the cardio-respiratory system may also be an important factor constraining the capacity for prey handling and ingestion.

Red blood cells from the South American rattlesnake (Crotalus durissus terrificus) regulate volume incompletely following osmotic shrinkage and swelling in vitro

The ability of rattlesnake (Crotalus durissus terrificus) red blood cells to volume regulate in vitro has been investigated. Blood was drawn through a catheter inserted in the dorsal aorta and equilibrated to gas mixtures of different composition. Cells shrunken osmotically by increasing the extracellular osmolarity from approximately 291 mosm l(-1) (n=3) to approximately 632 mosm l(-1) (calculated) only partially regulated their volume back towards the original volume either at pH 7.51+/-0.05 (mean+/-S.D., n=5) or pH 7. 20+/-0.06 (mean+/-S.D., n=3). There was no improvement of the regulatory volume increase at low haemoglobin oxygen saturation. The limited volume restoration was inhibited by separate additions of amiloride (10(-4) M) or DIDS (10(-4) M) suggesting involvement of the Na(+)/H(+) and Cl(-)/HCO(3)(-) exchangers. Cells that were swollen osmotically by an approximately 30% dilution of the extracellular medium also exhibited a limited ability to recover their volume. Therefore, these cells show little ability to volume regulate when exposed to in vitro conditions that shrink or swell the cell.

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.

Functional and historical determinants of shape in the scapula of Xenarthran mammals: evolution of a complex morphological structure

The mammalian scapula is a complex morphological structure, composed of two ossification plates that fuse into a single structure. Most studies on morphological differentiation in the scapula have considered it to be a simple, spatially integrated structure, primarily influenced by the important locomotor function presented by this element. We used recently developed geometric morphometric techniques to test and quantify functional and phylogenetic influences on scapular shape variation in fossil and extant xenarthran mammals. The order Xenarthra is well represented in the fossil record and presents a stable phylogenetic hypothesis for its genealogical history. In addition, its species present a large variety of locomotor habits. Our results show that approximately half of the shape variation in the scapula is due to phylogenetic heritage. This is contrary to the view that the scapula is influenced only by functional demands. There are large-scale shape transformations that provide biomechanical adaptation for the several habits (arboreality, terrestriality, and digging), and small scale-shape transformations (mostly related to the coracoid process) that are not influenced by function. A nonlinear relationship between morphometric and phylogenetic distances indicates the presence of a complex mixture of evolutionary processes acting on shape differentiation of the scapula.

Temperature effects on lung and blood gases in Bufo paracnemis: consequences of bimodal gas exchange

The arterial pH decreases with rising body temperature in ectothermic vertebrates. We report on how this regulation was achieved in relation to bimodal respiration in the toad Bufo paracnemis. Gas exchange was measured for the lung and also for the whole body (skin and lung). In addition, lung gas pressures (PL(O2) and PL(CO2)) and arterial blood gases (pH and P(O2)) were measured at 17, 27 and 35 degrees C. Arterial pH fell from 7.85 at 17-7.64 at 35 degrees C. Concomitantly, PL(CO2) increased from 5.6 mmHg at 17 degrees C to 10.4 mmHg at 35 degrees C. Regardless of temperature, PL(O2) remained virtually constant at 125-126 mmHg, whereas arterial P(O2) increased significantly with rising temperature (50 mmHg at 17 degrees C; 79 mmHg at 35 degrees C). The pulmonary gas exchange ratio (RE) increased from 0.28 at 17 degrees C to 0.51 at 35 degrees C, while the ratio for whole body gas exchange (lung + skin) was close to 0.8 irrespective of temperature. Since CO2 conductance of the skin increased little with temperature, the lung eliminated a larger fraction of total CO2 output. This shift caused the increase of RE for pulmonary exchange with rising temperature, which increased PL(CO2) and contributed to a negative deltapHa/deltaT. Therefore, bimodal respiration in Bufo accounted for part of the temperature-dependent pH regulation, while the final adjustments depend on pulmonary ventilation.

Evaporative water loss and oxygen uptake in two casque-headed tree frogs, Aparasphenodon brunoi and Corythomantis greeningi (Anura, Hylidae)

Evaporative water loss (EWL) and oxygen uptake (Vo2) was measured in two species of tree frogs with cranial co-ossification, Aparasphenodon brunoi and Corythomantis greeningi. Both species use their head to seal the entrance of bromeliads, tree holes or rocky crevices used as shelters. EWL was significantly reduced in sheltered individuals of both species as compared with those exposed nude to desiccation. EWL per unit area through the head surface was significantly lower than the body skin for A. brunoi but not for C. greeningi, EWL per unit surface area through C. greeningi body skin was about 50% that of A. brunoi, indicating a less permeable skin in the former species. The relationship between cranial coossification and EWL is discussed. Vo2 in A. brunoi was comparable with other anurans of similar size, whereas in C. greeningi, it was lower than predicted from body mass. Moreover, Vo2 in C. greeningi showed less sensitivity to temperature increase than in A. brunoi. C. greeningi occurs in a drier environment than A. brunoi, and this appears to be reflected in their EWL and Vo2 characteristics.

Estivation in South American amphibians and reptiles

A number of amphibians and reptiles have cyclic behavior, becoming inactive with the coming of the dry season. In South America this pattern of activity is common, particularly in savannah-like vegetation. During the dry season amphibians burrow into the mud or soil, and either form a cocoon or increase the osmotic concentration of body fluids to reduce evaporative water loss. Some phyllomedusid tree frogs coat their body surface with skin secretion and excrete uric acid to minimize water loss. Reptiles also retreat into shelter deep enough to avoid temperature fluctuation during estivation or reduce metabolic response to temperature. Reduction of temperature sensitivity of the metabolism seems to be a strategy common to estivating amphibians and reptiles. Despite seasonal change of the environment, some species of reptiles are active all year round.

Development of blood pressure and cardiac reflexes in the frog Pseudis paradoxsus

Systemic arterial blood pressure and heart rate (fH) were measured in unanesthetized, unrestrained larvae and adults of the paradoxical frog, Pseudis paradoxus from São Paulo State in Brazil. Four developmental groups were used, representing the complete transition from aquatic larvae to primarily air-breathing adults. fH (49-66 beats/min) was not significantly affected by development, whereas mean arterial blood pressure was strongly affected, being lowest in the stage 37-39 larvae (10 mmHg), intermediate in the stage 44-45 larvae (18 mmHg), and highest in the juveniles and adults (31 and 30 mmHg, respectively). Blood pressure was not significantly correlated with body mass, which was greatest in the youngest larvae and smallest in the juveniles. In the youngest larvae studied (stages 37-39), lung ventilation was infrequent, causing a slight decrease in arterial blood pressure but no change in heart rate. Lung ventilation was more frequent in stages 44-45 larvae and nearly continuous in juveniles and adults floating at the surface. Bradycardia during both forced and voluntary diving was observed in almost every advanced larva, juvenile, and adult but in only one of four young larvae. Developmentally related changes in blood pressure were not complete until metamorphosis, whereas diving bradycardia was present at an earlier stage.

[Changes in body fluids of the frog Leptodactylus fuscus during estivation (Anura, Leptodactylidae)]

The frog, L. fuscus, becomes dormant during the dry season in southeastern Brazil. Plasma and urine were obtained and analyzed for K+, Na+, and osmotic concentrations in active and estivating frogs. Soil water potential from the estivation sites was compared with the osmotic concentrations of the frog. Plasma and urine osmotic concentrations (286.2 +/- 13.8 and 242.3 +/- 17.2 mOsm1(-1), respectively) were higher in the estivating than in active frogs (240.3 +/- 12.8 and 112.7 +/- 15.6 mOsm1(-1); plasma and urine), and the same holds true for plasma K+ content. The Na+ concentration was the same for active and estivating frogs. Soil water potential corresponded to osmotic pressure of 110 mOsm1(-1), showing that L. fuscus may uptake water from the soil during the estivation.

Control of breathing in an amphibian Bufo paracnemis: effects of temperature and hypoxia

Lung ventilation was measured in the toad, Bufo paracnemis, weight 500-800 g, at 15, 25 and 32 degree C during normoxia and hypoxia (5, 10, and 15% inspired O2). Arterial blood gases were measured during normoxic breathing. Typically breath-holds alternated with ventilatory periods, which were initiated by a stepwise pulmonary deflation. Then a series of breaths consisting of both expiratory and inspiratory volumes followed. At the end of the period the lungs were inflated in several steps. Increased temperature markedly augmented ventilation mostly through a five-fold increase in the number of ventilatory periods per unit time. Ventilation was also enhanced by hypoxia and this response was greatest at the highest temperature. Arterial PO2 rose from 35 to 96 Torr when temperature increased from 15 to 32 degrees C. Bufo resembles reptiles regarding these responses.

Respiratory properties of whole blood and hemoglobin from the burrowing reptile, Amphisbaena alba

Respiratory properties of whole blood and hemoglobin solutions have been studied in the burrowing reptile, Amphisbaena alba. Whole blood is distinguished from that of other squamate reptiles by an extraordinary high O2 affinity (P50 = 12 mmHg at pH 7.60 and 25 degrees C). The Bohr factor, phi, was large at -0.85 and the n-value was 1.80. O2 capacity averaged 12.0 vol%. The molar concentration of erythrocyte ATP was high and twice that of hemoglobin. Stripped Amphisbaena hemoglobin shows an extremely high O2 affinity and reduced pH sensitivity compared to whole blood (P50 = 1 mmHg at pH 7.60 and 25 degrees C, phi = -0.35, n-value = 2.0). The hemoglobin O2 affinity was much more sensitive to ATP than for other poikilotherm vertebrates. Isoelectric focusing revealed a multicomponent hemoglobin with the major components showing similar O2 affinities and Bohr shifts. The data obtained are discussed in relation to the burrowing habits of Amphisbaena and found to be adaptive to a fossorial mode of life.