Regulation of digestive performance: a proposed adaptive response

Among snakes a correlation exists between feeding habits (frequent or infrequent) and the magnitude by which digestive performance is regulated (modest or large). This paper investigates whether the observed regulation of digestive performance is an adaptation to feeding habits and therefore, a product of natural selection. Using data on metabolic and intestinal responses to feeding for amphibians and reptiles, it is attempted to show the selective advantage and independent origin of either modestly or widely regulating gut performance. In an energetic model, snakes that naturally feed frequently on small meals benefit (from lower energy output) from modestly regulating gut performance as opposed to widely regulating gut performance. Likewise, the model suggests an energetic benefit for infrequently-feeding snakes secondary to the wide regulation of gut performance. This benefit is a function of long spans of fasting with a down-regulated gut (thereby incurring a lower standard metabolic rate) and the occasionally incursion of a costly up-regulation of the gut. In a comparison across several distantly-related lineages of amphibians and reptiles, frequently-feeding species all exhibit small postprandial responses in metabolism and intestinal nutrient transport capacities. In contrast, frogs and snakes that routinely fast for long periods independently experience five- to 30-fold increases in metabolism and intestinal performance with feeding. Among amphibians and reptiles the evidence presented supports the hypothesis that the extent by which the gut is regulated is an adaptive trait that evolved with divergence in feeding habits and energy budgets. In finishing, the foundations, caveats, and suggested future tests of this adaptive hypothesis are presented.     

Respiratory consequences of feeding in the snake Python molorus

Snakes can ingest large meals and exhibit marked increases in metabolic rate during digestion. Because postprandial oxygen consumption in some snakes may surpass that attained during exercise, studies of digestion offers an alternative avenue to understand the cardio-respiratory responses to elevated metabolic rate in reptiles. The effects of feeding on metabolic rate, arterial oxygen levels, and arterial acid-base status in the snake Python molorus are described. Four snakes (180-250 g) were cannulated in the dorsal aorta and blood samples were obtained during 72 h following ingestion of a meal (rat pups) exceeding 20% of body weight. Oxygen consumption increased from a fasting value of 1.71 +/- 0.08 to 5.54 +/- 0.42 ml kg-1 min-1 at 48 h following feeding, and the respiratory gas exchange ratio increased from 0.67 +/- 0.02 to a maximum of 0.92 +/- 0.03 at 32 h. Plasma lactate was always less than 0.5 mM, so the postprandial increase in metabolic rate was met by aerobic respiration. In fasting animals, arterial PO2 was 66 +/- 4 mmHg and haemoglobin-O2 saturation was 92 +/- 3%; similar values were recorded during digestion, but haematocrit decreased from 15.8 +/- 1.0 to 9.8 +/- 0.8 due to repeated blood sampling. Plasma [HCO3-] increased from a fasting level of 19.3 +/- 0.8 to 25.8 +/- 1.0 mmol l-1 at 24 h after feeding. However, because arterial PCO2 increased from 21.1 +/- 0.5 to 27.9 +/- 1.4 mmHg, there was no significant change in arterial pH from the fasting value of 7.52 +/- 0.01. Acid-base status returned to pre-feeding levels at 72 h following feeding. The increased arterial PCO2 is most likely explained by a reduction in ventilation relative to metabolism, but we predict that lung PO2 does not decrease below 115 mmHg. Although ingestion of large meals is associated with large metabolic changes in pythons, the attendant changes in blood gases are relatively small. In particular, the small changes in plasma [HCO3-] and stable pH show that pythons respond very differently to digestion than alligators where very large alkaline tides have been observed. It is unclear why pythons and alligators differ in the magnitude of their responses, but given these interspecific differences it seems worthwhile to describe arterial blood gases during digestion in other species of ectothermic vertebrates.     

The influence of circadian rhythms on pre- and post-prandial metabolism in the snake Lamprophis fuliginosus

Measuring standard metabolic rate (SMR) and specific dynamic action (SDA) has yielded insight into patterns of energy expenditure in snakes, but less emphasis has been placed on identifying metabolic variation and associated energy cost of circadian rhythms. To estimate SMR, SDA, and identify metabolic variation associated with circadian cycles in nocturnally active African house snakes (Lamprophis fuliginosus), we measured oxygen consumption rates (VO2) at frequent intervals before and during digestion of meals equaling 10%, 20% and 30% of their body mass. Circadian rhythms in metabolism were perceptible in the VO2 data during fasting and after the initial stages of digestion. We estimated SMR of L. fuliginosus (mean mass=16.7+/-0.3 g) to be 0.68+/-0.02 (+/-SEM) mL O2/h at 25 degrees C. Twenty-four hours after eating, VO2 peaked at 3.2-5.3 times SMR. During digestion of meals equaling 10-30% of their body mass, the volume of oxygen consumed ranged from 109 to 119 mL O2 for SMR, whereas extra oxygen consumed for digestion and assimilation ranged from 68 to 256 mL O2 (equivalent to 14.5-17.0% of ingested energy). The oxygen consumed due to the rise in metabolism during the active phase of the daily cycle ranged from 55 to 66 mL O2 during digestion. Peak VO2, digestive scope, and SDA increased with increasing meal size. Comparisons of our estimates to estimates derived from methods used in previous investigations resulted in wide variance of metabolic variables (up to 39%), likely due to the influence of circadian rhythms and activity on the selection of baseline metabolism. We suggest frequent VO2 measurements over multiple days, coupled with mathematical methods that reduce the influence of undesired sources of VO2 variation (e.g., activity, circadian cycles) are needed to reliably assess SMR and SDA in animals exhibiting strong circadian cycles.     

Cooking and grinding reduces the cost of meat digestion

The cooking of food is hypothesized to have played a major role in human evolution partly by providing an increase in net energy gain. For meat, cooking compromises the structural integrity of the tissue by gelatinizing the collagen. Hence, cooked meat should take less effort to digest compared to raw meat. Likewise, less energy would be expended digesting ground meat compared to intact meat. We tested these hypotheses by assessing how the cooking and/or grinding of meat influences the energy expended on its digestion, absorption, and assimilation (i.e., specific dynamic action, SDA) using the Burmese python, Python molurus. Pythons were fed one of four experimental diets each weighing 25% of the snake's body mass: intact raw beef, intact cooked beef, ground raw beef, and ground cooked beef. We measured oxygen consumption rates of snakes prior to and up to 14 days following feeding and calculated SDA from the extra oxygen consumed above standard metabolic rate. Postprandial peak in oxygen consumption, the scope of peak rates, and SDA varied significantly among meal treatments. Pythons digesting raw or intact meals exhibited significantly larger postprandial metabolic responses than snakes digesting the cooked ground meals. We found cooking to decrease SDA by 12.7%, grinding to decrease SDA by 12.4%, and the combination of the two (cooking and grinding) to have an additive effect, decreasing SDA by 23.4%. These results support the hypothesis that the consumption of cooked meat provides an energetic benefit over the consumption of raw meat.     

Postprandial responses in the African rhombig egg eater (Dasypeltis scabra)

The African rhombic egg eater (Dasypeltis scabra) is a colubrid snake feeding exclusively on bird eggs. Frequency of feeding is governed by the seasonal availability of bird eggs; i.e., long fasting intervals change with relatively short periods when plenty of food is available. Intermittent feeding snakes show a remarkable postprandial increase of metabolic rate and digestive organ size. The postprandial increase in metabolic rate (specific dynamic action, SDA) in snakes is affected by meal size, temperature, and meal composition. A major portion of SDA in snakes is allocated to gastric function and the breakdown of the meal. We hypothesize that SDA in egg eaters is lower than in other snake species, because egg eaters feed on “liquid” food that does not require enzymatic breakdown in the stomach. We also hypothesized that other components of the postprandial response of egg eaters (e.g., size changes of the intestine and the liver) do not differ from other snakes. The standard metabolic rate and metabolic response to feeding were measured using closed-chamber respirometry. Size changes of small intestine and liver were measured using high-resolution transcutaneous ultrasonography. Standard metabolic rates of fasting egg eaters were in the same range of mass specific values as known from other snakes. Within 24 h after feeding, oxygen consumption doubled and peaked at 2 days after feeding. At the same time, the size of the small intestine and the cross-sectional diameter of the liver increased. Within 2 days after feeding, the size of the mucosal epithelium doubled its thickness. Liver size increased significantly within 24 h reaching maximum size 2–4 days after feeding. The size of both organs returned to fasting values within 7–10 days after feeding. The postprandial response of African rhombic egg eaters shows the same pattern and dynamics as known from other snake species. However, the factorial increase of metabolic rate during SDA is the lowest reported for any snake. A comparison with literature data supports the idea that SDA is mainly determined by gastric function and that it is low in egg eaters because they do not have to break down solid meals in the stomach as other snake species do.     

Specific dynamic action: a review of the postprandial metabolic response

For more than 200 years, the metabolic response that accompanies meal digestion has been characterized, theorized, and experimentally studied. Historically labeled “specific dynamic action” or “SDA”, this physiological phenomenon represents the energy expended on all activities of the body incidental to the ingestion, digestion, absorption, and assimilation of a meal. Specific dynamic action or a component of postprandial metabolism has been quantified for more than 250 invertebrate and vertebrate species. Characteristic among all of these species is a rapid postprandial increase in metabolic rate that upon peaking returns more slowly to prefeeding levels. The average maximum increase in metabolic rate stemming from digestion ranges from a modest 25% for humans to 136% for fishes, and to an impressive 687% for snakes. The type, size, composition, and temperature of the meal, as well as body size, body composition, and several environmental factors (e.g., ambient temperature and gas concentration) can each significantly impact the magnitude and duration of the SDA response. Meals that are large, intact or possess a tough exoskeleton require more digestive effort and thus generate a larger SDA than small, fragmented, or soft-bodied meals. Differences in the individual effort of preabsorptive (e.g., swallowing, gastric breakdown, and intestinal transport) and postabsorptive (e.g., catabolism and synthesis) events underlie much of the variation in SDA. Specific dynamic action is an integral part of an organism’s energy budget, exemplified by accounting for 19–43% of the daily energy expenditure of free-ranging snakes. There are innumerable opportunities for research in SDA including coverage of unexplored taxa, investigating the underlying sources, determinants, and the central control of postprandial metabolism, and examining the integration of SDA across other physiological systems.     

Effects of temperature on the metabolic response to feeding in Python molurus

As ectothermic vertebrates, reptiles undergo diurnal and seasonal changes in body temperature, which affect many biological functions. In conjunction with a general review regarding the effects of temperature on digestion in reptiles, we describe the effects of various temperatures (20-35 degrees C) on the metabolic response to digestion in the Burmese python (Python molurus). The snakes were fed mice amounting to 20% of their body weight and gas exchange (oxygen uptake and CO(2) production) were measured until digestion had ended and gas exchange returned to fasting levels. Elevated temperature was associated with a faster and larger metabolic increase after ingestion, and the time required to return to fasting levels was markedly longer at low temperature. The factorial increase between fasting oxygen consumption (VO(2)) and maximal VO(2) during digestion was, however, similar at all temperatures studied. Furthermore, the integrated SDA response was not affected by temperature suggesting the costs associated with digestion are temperature-independent. Other studies on reptiles show that digestive efficiency is only marginally affected by temperature and we conclude that selection of higher body temperatures during digestion (postprandial thermophilic response) primarily reduces the time required for digestion.     

Testing the 'free radical theory of aging' hypothesis: physiological differences in long-lived and short-lived colubrid snakes

We test the 'free radical theory of aging' using six species of colubrid snakes (numerous, widely distributed, non-venomous snakes of the family Colubridae) that exhibit long (> 15 years) or short (< 10 years) lifespans. Because the 'rate of living theory' predicts metabolic rates to be correlated with rates of aging and oxidative damage results from normal metabolic processes we sought to answer whether physiological parameters and locomotor performance (which is a good predictor of survival in juvenile snakes) mirrored the evolution of lifespans in these colubrid snakes. We measured whole animal metabolic rate (oxygen consumption Vo2), locomotor performance, cellular metabolic rate (mitochondrial oxygen consumption), and oxidative stress potential (hydrogen peroxide production by mitochondria). Longer-lived colubrid snakes have greater locomotor performance and reduced hydrogen peroxide production than short-lived species, while whole animal metabolic rates and mitochondrial efficiency did not differ with lifespan. We present the first measures testing the 'free radical theory of aging' using reptilian species as model organisms. Using reptiles with different lifespans as model organisms should provide greater insight into mechanisms of aging.     

Metabolic response to feeding in the Chinese striped-necked turtle, Ocadia sinensis

We measured oxygen consumption in juvenile Chinese striped-necked turtles (Ocadia sinensis) after they ingested food, either as a single meal or as double meals, to examine the influence of meal type and feeding frequency on specific dynamic action (SDA). Temporal variation in oxygen consumption after feeding was evident in the ingesting turtles but not in the unfed control turtles. In the single-meal experiment, the peak metabolic rate and the integrated SDA response (the whole energetic cost for the processes of digestion) both did not differ between turtles ingesting mealworms and shrimps when the influence of variation in ingested energy was removed, and the time to reach peak metabolic rate was not affected by meal type and the amount of food ingested. Turtles in the double-meal experiment ingested more energy and hence had a prolonged duration of SDA response than did those in the single-meal experiment, but the integrated SDA response did not differ between both experimental treatments when the influence of variation in ingested energy was removed. Our results show that meal type and feeding frequency have important consequences on the SDA response of juvenile O. sinensis. As the integrated SDA response remained remarkably constant either between turtles ingesting different food or between turtles ingesting the same food but at different frequencies when the influence of variation in ingested energy was removed, we therefore conclude that the energetic cost associated with ingestion is primarily determined by energy content of food ingested in juvenile O. sinensis.     

Cold physiology: postprandial blood flow dynamics and metabolism in the Antarctic fish Pagothenia borchgrevinki

Previous studies on metabolic responses to feeding (i.e. the specific dynamic action, SDA) in Antarctic fishes living at temperatures below zero have reported long-lasting increases and small peak responses. We therefore hypothesized that the postprandial hyperemia also would be limited in the Antarctic fish Pagothenia borchgrevinki. The proportion of cardiac output directed to the splanchnic circulation in unfed fish was 18%, which is similar to temperate fish species. Contrary to our prediction, however, gastrointestinal blood flow had increased by 88% at twenty four hours after feeding due to a significant increase in cardiac output and a significant decrease in gastrointestinal vascular resistance. While gastric evacuation time appeared to be longer than in comparable temperate species, digestion had clearly commenced twenty four hours after feeding as judged by a reduction in mass of the administered feed. Even so, oxygen consumption did not increase suggesting an unusually slowly developing SDA. Adrenaline and angiotensin II was injected into unfed fish to investigate neuro-humoral control mechanisms of gastrointestinal blood flow. Both agonists increased gastrointestinal vascular resistance and arterial blood pressure, while systemic vascular resistance was largely unaffected. The hypertension was mainly due to increased cardiac output revealing that the heart and the gastrointestinal vasculature, but not the somatic vasculature, are important targets for these agonists. It is suggested that the apparently reduced SDA in P. borchgrevinki is due to a depressant effect of the low temperature on protein assimilation processes occurring outside of the gastrointestinal tract, while the gastrointestinal blood flow responses to feeding and vasoactive substances resemble those previously observed in temperate species.     

Metabolic response to feeding in the Chinese striped-necked turtle, Ocadia sinensis

We measured oxygen consumption in juvenile Chinese striped-necked turtles (Ocadia sinensis) after they ingested food, either as a single meal or as double meals, to examine the influence of meal type and feeding frequency on specific dynamic action (SDA). Temporal variation in oxygen consumption after feeding was evident in the ingesting turtles but not in the unfed control turtles. In the single-meal experiment, the peak metabolic rate and the integrated SDA response (the whole energetic cost for the processes of digestion) both did not differ between turtles ingesting mealworms and shrimps when the influence of variation in ingested energy was removed, and the time to reach peak metabolic rate was not affected by meal type and the amount of food ingested. Turtles in the double-meal experiment ingested more energy and hence had a prolonged duration of SDA response than did those in the single-meal experiment, but the integrated SDA response did not differ between both experimental treatments when the influence of variation in ingested energy was removed. Our results show that meal type and feeding frequency have important consequences on the SDA response of juvenile O. sinensis. As the integrated SDA response remained remarkably constant either between turtles ingesting different food or between turtles ingesting the same food but at different frequencies when the influence of variation in ingested energy was removed, we therefore conclude that the energetic cost associated with ingestion is primarily determined by energy content of food ingested in juvenile O. sinensis.     

Gastrointestinal blood flow and postprandial metabolism in swimming sea bass Dicentrarchus labrax

In trout and salmon, the metabolic costs of exercise and feeding are additive, which would suggest that gastrointestinal blood flow during exercise is maintained to preserve digestive and absorptive processes related to the specific dynamic action (SDA) of food. However, in most published studies, gastrointestinal blood flow drops during swimming, hypoxia, and general stress. To test whether gastrointestinal blood flow is spared during exercise after feeding, sea bass were instrumented with flow probes to measure cardiac output and celiacomesenteric blood flow while swimming in a respirometer before and after feeding. Swimming at 2 body lengths per second (bl s(-1)) increased metabolic rate considerably more than did feeding (208% vs. 32% increase, respectively, relative to resting), and a similar pattern was observed for cardiac output. In unfed fish, resting gastrointestinal blood flow was 13.8+/-0.5 mL min(-1) kg(-1). After feeding, resting gastrointestinal blood flow increased by 82% but then decreased progressively with increasing swimming speeds. At 2 bl s(-1), gastrointestinal blood flow in fed fish was not significantly different compared with that in unfed swimming fish, and, therefore, the data do not support the gastrointestinal sparing hypothesis. The magnitude of the SDA was maintained despite the decrease in gastrointestinal blood flow and the consequent reduction in oxygen supply to the gut. An estimate of maximal oxygen flow to the gastrointestinal tract after feeding yielded 2.6 mmol O(2) h(-1) kg(-1), but this amount is not able to cover the oxygen demand of 3.16 mmol O(2) h(-1) kg(-1). Therefore, the SDA must reflect metabolic processes in tissues other than those directly perfused by the celiacomesenteric artery.     

The relationships between specific dynamic action,nutrient retention and feed conversion ratio in farmed freshwater Chinook salmon (Oncorhynchus tshawytscha)

Improving the feed conversion ratio (FCR; the amount of feed consumed relative to the amount of weight gain) can reduce both production costs and environmental impacts of farmed fish. The aim of this study was to investigate what drives FCR to understand how nutrients are retained, as well as the amount of oxygen consumed for digestion, absorption and assimilation (a metabolic process known as specific dynamic action, SDA). Feed-efficient and inefficient Chinook salmon (Oncorhynchus tshawytscha) in fresh water were identified using ballotini beads and X-radiography that tracked individual feed intake across three assessment periods under satiated feeding. This allowed a comparison of physiological traits and body composition between the two FCR phenotypes over two time points as Chinook salmon grew from 305 to 620 g. Fish with higher daily feed intake (DFI) had higher daily weight gain (DWG) as expected. Nonetheless, the relationship between FCR and DFI as well as FCR and DWG was variable between time points. FCR and DWG were not correlated at the first time point and were negatively correlated at the second time point. In contrast, FCR and DFI were positively correlated at the first time point but not the second. Despite this, efficient fish ate smaller meals and retained more protein, lipid and energy in their body tissues. There was no detectable difference in metabolism between the two FCR phenotypes with respect to minimal resting metabolic rate, maximum metabolic rate, aerobic scope, or SDA parameters. In conclusion, FCR is not consistently associated with growth and metabolic differences in freshwater Chinook salmon, but FCR-efficient fish retain more nutrients and consume smaller meals.     

The Reptilian Baroreceptor and Its Role in Cardiovascular Control

Anatomical evidence for the existence of a depressor nerve inreptiles was first reported 100 years ago. Electrical stimulationof the central end of the cut nerve, however, did not producean unequivocal fall in heart rate and blood pressure, so itwas thought not to function as a depressor nerve. This remainedthe state of knowledge for fifty years when Marco Fedele performeda superb anatomical and physiological study of the depressornerves of turtles and lizards. He demonstrated that there weretwo depressor nerves from each vagus; the superior nerve originatedfrom the jugular ganglion or superior laryngeal nerve in turtlesand from the superior laryngeal nerve or vagus in lizards; theinferior nerve originated from the nodose ganglion or slightlycaudad of this ganglion. The nerves were shown to terminatein the proximal truncus arteriosus. Unlike the earlier workers,Fedele obtained a clear depressor effect on stimulating thedepressor nerves. In more recent times baroreflexes have been demonstrated inresponse to hemorrhage and body tilting in reptiles, with snakesreceiving particular attention. The evidence indicates thataquatic snakes are less effective at maintaining blood pressurethan terrestrial and arboreal forms. The sensitivity (gain)of the baroreceptor-heart rate reflex, when it is expressedas a percentage change in heart rate per unit pressure change,is approximately the same in reptiles, amphibians, and mammals.In addition, the ultrastructural appearance of the baroreceptorsof lizards is similar to that of mammals. A quantitative assessmentof the ability of reptiles to correct disturbances in bloodpressure has not yet been made, but techniques for obtainingthis information are now available.     

Expression pattern of three-finger toxin and phospholipase A2 genes in the venom glands of two sea snakes, Lapemis curtus and Acalyptophis peronii : comparison of evolution of these toxins in land snakes, sea kraits and sea snakes

Background  

Snake venom composition varies widely both among closely related species and within the same species, based on ecological variables. In terrestrial snakes, such variation has been proposed to be due to snakes' diet. Land snakes target various prey species including insects (arthropods), lizards (reptiles), frogs and toads (amphibians), birds (aves), and rodents (mammals), whereas sea snakes target a single vertebrate class (fishes) and often specialize on specific types of fish. It is therefore interesting to examine the evolution of toxins in sea snake venoms compared to that of land snakes.     

The effect of meal composition on specific dynamic action in burmese pythons (Python molurus)

We quantified the specific dynamic action (SDA) resulting from the ingestion of various meal types in Burmese pythons (Python molurus) at 30 degrees C. Each snake was fed a series of experimental meals consisting of amino acid mixtures, simple proteins, simple or complex carbohydrates, or lipids as well as meals of whole animal tissue (chicken breast, beef suet, and mouse). Rates of oxygen consumption were measured for approximately 4 d after feeding, and the increment above standard metabolic rate was determined and compared to energy content of the meals. While food type (protein, carbohydrate, and lipid) had a general influence, SDA was highly dependent on meal composition (i.e., amino acid composition and carbohydrate structure). For chicken breast and simple carbohydrates, the SDA coefficient was approximately one-third the energetic content of the meal. Lard, suet, cellulose, and starch were not digested and did not produce measurable SDA. We conclude that the cost of de novo protein synthesis is an important component of SDA after ingestion of protein meals because (1) simple proteins, such as gelatin and collagen, did not stimulate levels of SDA attained after consumption of complete protein, (2) incomplete mixtures of amino acids failed to elicit the SDA of a complete mixture, and (3) the inhibition of de novo protein synthesis with the drug cycloheximide caused a more than 70% decrease in SDA. Stomach distension and mechanical digestion of intact prey did not cause measurable SDA.     

Blood supply of the compact and spongy myocardium of fish, amphibia and reptiles]

Coronal arteries were injected with lead carbonate suspension and with Indian ink and cleared preparations 150--300 mkm thick were made in 195 hearts of fish, amphibians and reptiles and studied roentgenographically. It was stated that in Chondrichthyes (shark, skate) and in Chondrostei (beluga, stellate sturgeon, sturgeon), as well as in alligator both compact and spongy myocardium of the cardiac ventricle possess blood vessels. In teleostei, amphibians and reptiles (except alligator) spongy myocardium is avascular and receives its nutrition from the ventricle. In view of the data on the presence of blood vessels in the spongy myocardium in some vertebrates, it is impossible to accept the theory suggested by Grant and Regnier according to which vessels in the heart walls appear only in connection with compactization of the myocardium. Vascularization of the spongy myocardium is closely connected with oxygen saturation of the blood flowing through the heart. When this saturation is not satisfactory, the spongy myocardium has blood vessels. In alligator, vascularization of the spongy myocardium is connected with the fact that the heart has four chambers and there are arterial and venous blood streams.     

Reptiles as potential vectors and hosts of the amphibian pathogen Batrachochytrium dendrobatidis in Panama

Chytridiomycosis, the disease caused by Batrachochytrium dendrobatidis, is considered to be a disease exclusively of amphibians. However, B. dendrobatidis may also be capable of persisting in the environment, and non-amphibian vectors or hosts may contribute to disease transmission. Reptiles living in close proximity to amphibians and sharing similar ecological traits could serve as vectors or reservoir hosts for B. dendrobatidis, harbouring the organism on their skin without succumbing to disease. We surveyed for the presence of B. dendrobatidis DNA among 211 lizards and 8 snakes at 8 sites at varying elevations in Panama where the syntopic amphibians were at pre-epizootic, epizootic or post-epizootic stages of chytridiomycosis. Detection of B. dendrobatidis DNA was done using qPCR analysis. Evidence of the amphibian pathogen was present at varying intensities in 29 of 79 examined Anolis humilis lizards (32%) and 9 of 101 A. lionotus lizards (9%), and in one individual each of the snakes Pliocercus euryzonus, Imantodes cenchoa, and Nothopsis rugosus. In general, B. dendrobatidis DNA prevalence among reptiles was positively correlated with the infection prevalence among co-occurring anuran amphibians at any particular site (r = 0.88, p = 0.004). These reptiles, therefore, may likely be vectors or reservoir hosts for B. dendrobatidis and could serve as disease transmission agents. Although there is no evidence of B. dendrobatidis disease-induced declines in reptiles, cases of coincidence of reptile and amphibian declines suggest this potentiality. Our study is the first to provide evidence of non-amphibian carriers for B. dendrobatidis in a natural Neotropical environment.     

The herpetofauna of Timor-Leste: a first report

Fieldwork conducted throughout Timor-Leste in September 2004 and July 2009 resulted in a collection or recording of 263 herpetological specimens (100 amphibians, 163 reptiles), comprising at least seven species of frogs and toads, 20 species of lizards, seven species of snakes, two species of turtles, and one species of crocodile. Among the amphibians, the most frequently encountered species were toads (Duttaphrynus melanostictus), rice paddy frogs (genus Fejervarya), and rhacophorid treefrogs (Polypedates cf. leucomystax). All three variants of rice paddy frogs encountered represent undescribed species similar to Fejervarya verruculosa from neighboring Wetar Island. Records of Fejervarya cancrivora and Fejervarya limnocharis for Timor Island are apparently errors based on misidentification. We obtained voucher specimens for a total of 147 lizards and voucher photographs only for four specimens of Varanus timorensis. Aside from geckos frequently associated with human habitations (e.g., Gehyra mutilata, Gekko gecko, Hemidactylus frenatus, Hemidactylus platyurus), we discovered an as yet undescribed species of bent-toed gecko, genus Cyrtodactylus, in the Same valley. Our specimens of Hemidactylus platyurus are the first record of this species from Timor-Leste. Commonly encountered skinks included four-fingered skinks (genus Carlia), wedge skinks (genus Sphenomorphus), and night skinks (genus Eremiascincus). Notable among the 15 snakes collected was the frequency of pitvipers (Cryptelytrops insularis), which amounted to over 25% of all snakes. Our specimen of the wolfsnake Lycodon subcinctus is the first record of this species for Timor-Leste. Based on these findings, it appears that the biodiversity of amphibians and reptiles in this remote corner of Wallacea is much greater than previously thought, particularly with respect to scincid lizards. The detail we provide in the species accounts is designed to allow the use of this report as a preliminary field guide to the amphibians and reptiles of Timor-Leste. However, survey work is ongoing.     

Effects of inhibition gastric acid secretion on arterial acid-base status during digestion in the toad Bufo marinus

Digestion affects acid-base status, because the net transfer of HCl from the blood to the stomach lumen leads to an increase in HCO3(-) levels in both extra- and intracellular compartments. The increase in plasma [HCO3(-)], the alkaline tide, is particularly pronounced in amphibians and reptiles, but is not associated with an increased arterial pH, because of a concomitant rise in arterial PCO2 caused by a relative hypoventilation. In this study, we investigate whether the postprandial increase in PaCO2 of the toad Bufo marinus represents a compensatory response to the increased plasma [HCO3(-)] or a state-dependent change in the control of pulmonary ventilation. To this end, we successfully prevented the alkaline tide, by inhibiting gastric acid secretion with omeprazole, and compared the response to that of untreated toads determined in our laboratory during the same period. In addition, we used vascular infusions of bicarbonate to mimic the alkaline tide in fasting animals. Omeprazole did not affect blood gases, acid-base and haematological parameters in fasting toads, but abolished the postprandial increase in plasma [HCO3(-)] and the rise in arterial PCO2 that normally peaks 48 h into the digestive period. Vascular infusion of HCO3(-), that mimicked the postprandial rise in plasma [HCO3(-)], led to a progressive respiratory compensation of arterial pH through increased arterial PCO2. Thus, irrespective of whether the metabolic alkalosis is caused by gastric acid secretion in response to a meal or experimental infusion of bicarbonate, arterial pH is being maintained by an increased arterial PCO2. It seems, therefore, that the elevated PCO2, occuring during the postprandial period, constitutes of a regulated response to maintain pH rather than a state-dependent change in ventilatory control.