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 (PA). This hypotension elicits systemic vasoconstriction and tachycardia, which generally reduce blood pooling and increase PA 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 PA, heart rate (fH) 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' fH 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 PA at the beginning of body inclinations; and (3) α1-adrenergic orthostatic vasomotor responses are important for the maintenance of PA 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.

The Effects of Feeding on Cardiac Control of the Broad-Nosed Caiman (Caiman latirostris): The Role of the Autonomic Nervous System and NANC Factors.

The metabolic increment that occurs after feeding demands cardiovascular adjustments to be maintained, as increased heart rate (fH ) and cardiac output. In mammals, postprandial tachycardia seems to be triggered by an increase in adrenergic activity and by nonadrenergic noncholinergic (NANC) factors, while in ectothermic vertebrates, this adjustment seems to be linked to a withdrawal of vagal drive as well as to NANC factors. Because the factors behind postprandial tachycardia have not yet been investigated in crocodilians, the present study sought to evaluate the postprandial tachycardia mediators in the broad-nosed caiman. To this end, fasting and digesting animals were instrumented with intraperitoneal cannula and subcutaneous electrocardiogram electrodes (for the measurement of fH , cardiac autonomic tones, and total fH variability, as well as for a power spectral analysis of fH ). Data were then collected with the animals in an untreated state, as well as after muscarinic cholinergic blockade with atropine (2.5 mg kg-1 ) and after double autonomic blockade with atropine and propranolol (5.0 mg kg-1 ). Fasting animals' fH was ∼18 bpm, a value which increased to ∼30 bpm during digestion. After the double autonomic blockade, fasting animals exhibited an fH of ∼15 bpm, while digesting animals' fH was ∼23 bpm. This result is evidence of the presence of NANC factors with positive chronotropic effects acting during digestion. The calculated autonomic tones showed that, after feeding, the adrenergic tone increased while the cholinergic tone remained unchanged. Finally, fH variability analyses revealed that this adrenergic increase is primarily derived from circulating catecholamines.

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.

Autonomic control of post-air-breathing tachycardia in Clarias gariepinus (Teleostei: Clariidae).

The African catfish (Clarias gariepinus) is a teleost with bimodal respiration that utilizes a paired suprabranchial chamber located in the gill cavity as an air-breathing organ. Like all air-breathing fishes studied to date, the African catfish exhibits pronounced changes in heart rate (f H) that are associated with air-breathing events. We acquired f H, gill-breathing frequency (f G) and air-breathing frequency (f AB) in situations that require or do not require air breathing (during normoxia and hypoxia), and we assessed the autonomic control of post-air-breathing tachycardia using an infusion of the ß-adrenergic antagonist propranolol and the muscarinic cholinergic antagonist atropine. During normoxia, C. gariepinus presented low f AB (1.85 ± 0.73 AB h(-1)) and a constant f G (43.16 ± 1.74 breaths min(-1)). During non-critical hypoxia (PO2 = 60 mmHg), f AB in the African catfish increased to 5.42 ± 1.19 AB h(-1) and f G decreased to 39.12 ± 1.58 breaths min(-1). During critical hypoxia (PO2 = 20 mmHg), f AB increased to 7.4 ± 1.39 AB h(-1) and f G decreased to 34.97 ± 1.78 breaths min(-1). These results were expected for a facultative air breather. Each air breath (AB) was followed by a brief but significant tachycardia, which in the critical hypoxia trials, reached a maximum of 143 % of the pre-AB f H values of untreated animals. Pharmacological blockade allowed the calculation of cardiac autonomic tones, which showed that post-AB tachycardia is predominantly regulated by the parasympathetic subdivision of the autonomic nervous system.

Autonomic control of heart rate during orthostasis and the importance of orthostatic-tachycardia in the snake Python molurus.

Orthostasis dramatically influences the hemodynamics of terrestrial vertebrates, especially large and elongated animals such as snakes. When these animals assume a vertical orientation, gravity tends to reduce venous return, cardiac filling, cardiac output and blood pressure to the anterior regions of the body. The hypotension triggers physiological responses, which generally include vasomotor adjustments and tachycardia to normalize blood pressure. While some studies have focused on understanding the regulation of these vasomotor adjustments in ectothermic vertebrates, little is known about regulation and the importance of heart rate in these animals during orthostasis. We acquired heart rate and carotid pulse pressure (P PC) in pythons in their horizontal position, and during 30 and 60° inclinations while the animals were either untreated (control) or upon muscarinic cholinoceptor blockade and a double autonomic blockade. Double autonomic blockade completely eradicated the orthostatic-tachycardia, and without this adjustment, the P PC reduction caused by the tilts became higher than that which was observed in untreated animals. On the other hand, post-inclinatory vasomotor adjustments appeared to be of negligible importance in counterbalancing the hemodynamic effects of gravity. Finally, calculations of cardiac autonomic tones at each position revealed that the orthostatic-tachycardia is almost completely elicited by a withdrawal of vagal drive.

Hábitos alimentares de serpentes em Espigão do Oeste, Rondônia, Brasil / Food habits of snakes from Espigão do Oeste, Rondônia, Brazil

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 por cento), seguidos de mamíferos (16 por cento), lagartos (15 por cento), moluscos (13 por cento), aves (5 por cento) e serpentes (5 por cento). 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 por cento) forragearem sobre o chão.

The present study reports on food habits of snakes in Espigão do Oeste, Rondônia State (Southwestern Amazonia), Brazil. Snakes were recorded by time constrained search, pitfall traps with drift fences, captures by local inhabitants, and opportunistic sightings. The snakes collected had their stomachs and intestinal contents examined. Information on food habits was obtained for 89 specimens belonging to 31 species. The majority of the 114 items found (stomach contents and field observations) were adult frogs (38 percent), followed by mammals (16 percent), lizards (15 percent), mollusks (13 percent), birds (5 percent), and snakes (5 percent). The majority of snake species from Espigão do Oeste feed on lizards, as in Central Amazonia (Manaus). A smaller proportion of snakes in the Amazonia feed upon frogs in relation to the Pantanal, South and Southeastern Brazil. These differences may be due to greater proportion of Xenodontinae in extra-Amazonian communities, as many snakes in that clade prey upon frogs. Most of the frogs and lizards species recorded in stomach contents snakes are terrestrial, which should be associated with most species of analysed snakes (52 percent) foraging on the ground.

Aproveitamento de alimentos de origem animal pela tartaruga-da-amazônia: Podocnemis expansa criada em cativeiro / The use of animal feed in the diet of captive Arrau sideneck: Podocnemis expansa

Foi realizado um trabalho para determinar o aproveitamento alimentar da farinha de carne e ossos (FCO), farinha de vísceras de aves (FVA) e farinha de peixe (FP) em tartaruga-da-amazônia, por meio dos coeficientes de digestibilidade aparente (CDA) da matéria seca (MS), proteína bruta (PB), extrato etéreo (EE) e energia bruta (EB). Os animais experimentais foram 136 filhotes provenientes do Projeto Quelônios da Amazônia, no estado do Mato Grosso, mantidos em caixas com renovação de água e temperatura média de 29oC. Os CDA foram determinados com dietas contendo 0,1% do marcador óxido de crômio III (Cr2O3). Os CDA da MS, PB, EE e EB foram, respectivamente, de 79,10; 87,61; 93,83 e 79,61% para FCO; 92,45; 94,89; 96,55 e 92,71% para FV e 93,53; 95,13; 94,05 e 93,18% para FP. Os melhores coeficientes foram obtidos com a farinha de peixe e a farinha de vísceras de aves.

The effect of animal feed was studied in the Arrau sideneck, by the evaluation of apparent digestibility coefficient (ADC) of the dry matter (DM), crude protein (CP), ether extract (EE) and gross energy (GE) of the meat and bone meal (MBM), poultry by-products meal (PBM) and fish meal (FM). The turtles used were 136 hatchlings from Projeto Quelônios da Amazônia, State of Mato Grosso. Experimental animals were raised in plastic containers, with continuous water flow and mean temperature kept at 29oC. ADC was determined by the use of diets labeled with 0.1% of chromium oxide III (Cr2O3). The ADC of DM, CP, EE and GE were, respectively, 79.10, 87.61, 93.83 and 79.61% for MBM, 92.45, 94.89, 96.55 and 92.71% for PBM and 93.53, 95.13, 94.05 and 93.18% for FM. The best coefficients were obtained with the fish meal and poultry by-products meal.

Lagartos (Squamata: Lacertilia) em áreas de floresta e de pastagem em Espigão do Oeste, Rondônia, sudoeste da Amazônia, Brasil / Lizard community (Squamata: Lacertilia) in forest and pasture areas at Espigão do Oeste, Rondônia, southwestern Amazon, Brazil

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.

This study describes the richness and capture rates of lizards in forested and pasture areas at a locality in Rondônia (southwestern Amazon) utilizing three sampling methods: pitfall trap with drift fences, nocturnal time-constrained search and incidental finding. In all, 29 species belonging to nine families was recorded. Most species were found in forested area, whilst only eight species in pasture area. Most species were collected with pitfall trap (22), followed by incidental finding (16), and nocturnal search (9). The collecting curve gathering the three methods used showed that after the eighth month of sampling no new species could be added. This data suggests that the community was well sampled. The fact that some species were collect just by one of collecting method indicates the adequacy of using two or more methods for sampling communities. Higher species richness was recorded in forested areas compared with pastures. Such reduction is species number is due to the removing of plant covering and its consequences, the increasing predation rate, competition, food reduction, losses of sheltering and breeding, and limited thermoregulatory capacity.

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.