Effects of acclimation and acute temperature change on specific dynamic action and gastric processing in the green shore crab, Carcinus maenas

The effects of temperature acclimation and acute temperature change were investigated in postprandial green shore crabs, Carcinus maenas. Oxygen uptake, gut contractions and transit rates and digestive efficiencies were measured for crabs acclimated to either 10 °C or 20 °C and subsequently exposed to treatment temperatures of 5, 15, or 25 °C. Temperature acclimation resulted in a partial metabolic compensation in unfed crabs, with higher oxygen uptake rates measured for the 10 °C acclimated group exposed to acute test temperatures. The Q₁₀ values were higher than normal, probably because the acute temperature change prevented crabs from fully adjusting to the new temperature. Both the acclimation and treatment temperature altered the characteristics of the specific dynamic action (SDA). The duration of the response was longer for 20 °C acclimated crabs and was inversely related to the treatment temperature. The scope (peak oxygen consumption) was also higher for 20 °C acclimated crabs with a trend towards an inverse relationship with treatment temperature. Since the overall SDA (energy expenditure) is a function of both duration and scope, it was also higher for 20 °C acclimated crabs, with the highest value measured at the treatment temperature of 15 °C. The decline in total SDA after acute exposure to 5 and 25 °C suggests that both cold stress and limitations to oxygen supply at the temperature extremes could be affecting the SDA response. The contractions of the pyloric sac of the foregut region function to propel digesta through the gut, and contraction rates increased with increasing treatment temperature. This translated into faster transit rates with increasing treatment temperatures. Although pyloric sac contractions were higher for 20 °C acclimated crabs, temperature acclimation had no effect on transit rates. This suggests that a threshold level in pyloric sac contraction rates needs to be reached before it manifests itself on transit rates. Although there was a correlation between faster transit times and the shorter duration of the SDA response with increasing treatment temperature, transit rates do not make a good proxy for calculating the SDA characteristics. The digestive efficiency showed a trend towards a decreasing efficiency with increasing treatment temperature; the slower transit rates at the lower treatment temperatures allowing for more efficient nutrient absorption. Even though metabolic rates of 10 °C acclimated crabs were higher, there was no effect of acclimation temperature on digestive efficiency. This probably occurred because intracellular enzymes and digestive enzymes are modulated through different control pathways. These results give an insight into the metabolic and digestive physiology of Carcinus maenas as it makes feeding excursions between the subtidal and intertidal zones.     

Effects of meal size,meal type,and body temperature on the specific dynamic action of anurans

Specific dynamic action (SDA), the increase in metabolism stemming from meal digestion and assimilation, varies as a function of meal size, meal type, and body temperature. To test predictions of these three determinants of SDA, we quantified and compared the SDA responses of nine species of anurans, Bombina orientalis, Bufo cognatus, Ceratophrys ornata, Dyscophus antongilli, Hyla cinerea, Kassina maculata, Kassina senegalensis, Pyxicephalus adspersus, and Rana catesbeiana subjected to meal size, meal type, and body temperature treatments. Over a three to seven-fold increase in meal size, anurans experienced predicted increases in postprandial rates of oxygen consumption the duration of elevated and SDA. Meal type had a significant influence on the SDA response, as the digestion and assimilation of hard-bodied, chitinous crickets, mealworms, and superworms required 76% more energy than the digestion and assimilation of soft-bodied earthworms, waxworms, and neonate rodents. Body temperature largely effected the shape of the postprandial metabolic profile; peak increased and the duration of the response decreased with an increase in body temperature. Variation in body temperature did not significantly alter SDA for four species, whereas both H. cinerea and R. catesbeiana experienced significant increases in SDA with body temperature. For 13 or 15 species of anurans ranging in mass from 2.4 to 270 g, SMR, postprandial peak and SDA scaled with body mass (log–log) with mass exponents of 0.79, 0.93, and 1.05, respectively.     

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.     

Specific dynamic action and carbon incorporation in Calanus finmarchicus copepodites and females

Specific dynamic action (SDA) and incorporation of carbon into protein, lipids, and polysaccharides were measured in copepodite CV and adult female Calanus finmarchicus during the spring/summer growth season in Raunefjorden, Norway. Organic carbon from the food (Rhodomonas baltica) was allocated differently in the two developmental stages. Copepodites incorporated 50-80% of the carbon into lipids and only 7-22% into protein. Carbon incorporation into protein was higher in females, constituting 23% in May at 7 °C and 34% in June at 11 °C. This resulted in significant differences in the magnitude of SDA, measured as the increase in oxygen consumption during and after an 8-h feeding event. On average, the rate of carbon incorporation into protein was 2 times higher and the magnitude of SDA was 2.5 times higher in females than in copepodites. There was a significant correlation between the magnitude of SDA and carbon incorporation into protein suggesting that SDA is linked to protein synthesis. When comparing ATP equivalents of the magnitude of SDA with ATP equivalents of the total amount of carbon incorporated, more energy was produced than consumed. This supports speculations of an energy demand associated with a rapid turnover of newly synthesised protein.     

Gastric processing in the Dungeness crab, Cancer magister, during hypoxia

The gastric physiology of the Dungeness crab, Cancer magister, was investigated over a range of oxygen tensions. Postprandial crabs reacted differently to hypoxia compared with unfed animals. The bradycardic response in postprandial animals was reduced, suggesting a summation of responses with feeding. A similar pattern was observed for ventilation rate. In unfed animals ventilation rate increased slightly as oxygen levels declined, but dropped significantly in oxygen tensions below 3.2 kPa, whereas in postprandial crabs it increased significantly in the lower oxygen regimes. Gastric processing of the meal was followed using a fluoroscope. Pyloric contraction rates were maintained during mild hypoxia, but decreased in 5.3 kPa oxygen tension and below. This led to an increase in clearance times of digesta from the foregut, midgut and hindgut regions. The slowing of gastric processing in the lower oxygen tensions suggested that the animals were unable to maintain their internal oxygen concentration. A significant reduction in efficiency of assimilation only occurred in the lowest oxygen regime tested (1.6 kPa). The range of hypoxia where gastric processing was affected corresponded closely to the levels of oxygen that modulate the foraging behaviour of C. magister. By using both physiological and behavioural mechanisms C. magister can maintain digestive processes, even in severely oxygen depleted environments.     

Archival electronic tagging of a predatory sea star — Testing a new technique to study movement at the individual level

Sea stars are important marine predators, and their feeding often controls the distribution of associated species. Therefore, quantifying their activity at an individual level is important in further understanding how they structure marine communities. Sea stars are difficult to tag, so there is little information on activity of sea stars in their natural environment over extended periods of days to weeks. We tagged the New Zealand sea star Coscinasteriasmuricata with small archival electronic tags that recorded water temperate and depth every 5 min for up to 2 weeks. The tagging was undertaken to test the viability of using electronic tags in research on the ecology of the sea stars in a New Zealand fiord, where their vertical distribution is influenced by the presence of low-salinity layers. The effects of the tagging were tested in the laboratory and in the field, with tagging having no detectable influence on invitro survival, feeding rate, and righting time, or on their insitu movement and depth distribution. Laboratory experiments testing the salinity tolerance of C.muricata showed they could tolerate salinities as low as 25 PSU for at least a 20-day period. Tagging of sea stars in their natural environment provided information on depth distributions, vertical migrations and the influence of the physical environment on their behaviour. The tagging also revealed a large variation in activity at the individual level. This study represents one of the first to utilise electronic tagging to study the ecology of a mobile invertebrate such as a sea star. The success of this initial study suggests that we could gain valuable quantitative insight into the ecology of these animals in future tag deployments.     

Autotomy reduces feeding, energy storage and growth of the sea star Stichaster striatus

We evaluated the effect of autotomy on feeding, energy storage and growth of juvenile Stichaster striatus kept in the laboratory for five months with a limited supply of the mussel Semimytilus algosus. Autotomy strongly decreased feeding, energy storage and growth. Intact juveniles showed a ∼ 3 fold higher feeding rate than autotomized individuals throughout the experiment. Intact juveniles also had a higher (∼ 5 fold) energy content per pyloric caeca in each arm. This was mainly due to higher lipid content, the main proximate constituent of pyloric caeca. Intact juveniles showed a greater growth rate and reached a greater size than autotomized individuals, more evident for underwater mass than radius length. The reduced capacity to feed reduced energy intake in autotomized individuals. However, low energy reserves along with low growth in autotomized sea stars, support the hypothesis that juveniles of this species allocate energy to regeneration to the detriment of growth. This was also supported by the ∼ 25% of arm length regeneration after 5 mo. Remaining small could increase risk of lethal predation, however, S. striatus may reduce predation risk by using crevices and kelp holdfasts as refuges from predators. Given the strong impact of autotomy on feeding, regeneration of arms to recover full capacity to forage and grow seems a better strategy for juvenile S. striatus, than merely growing.     

动物特殊动力作用的研究进展

特殊动力作用（SDA）是指动物摄食过程中的代谢产热增加的现象,自上世纪初,一直受到相关领域专家的关注。近十年来该方面研究十分活跃。我们以南方鲇（Southern catfish／Silurus meridionalis）和鲇鱼（catfish／Silurus asotus）为实验对象,开展了大量相关研究。本文就我们的研究成果结合相关研究进行探讨,并指出了该方面研究将来可能的方向。     

Dysferlin is essential for endocytosis in the sea star oocyte

Dysferlin is a calcium-binding transmembrane protein involved in membrane fusion and membrane repair. In humans, mutations in the dysferlin gene are associated with muscular dystrophy. In this study, we isolated plasma membrane-enriched fractions from full-grown immature oocytes of the sea star, and identified dysferlin by mass spectrometry analysis. The full-length dysferlin sequence is highly conserved between human and the sea star. We learned that in the sea star Patiria miniata, dysferlin RNA and protein are expressed from oogenesis to gastrulation. Interestingly, the protein is highly enriched in the plasma membrane of oocytes. Injection of a morpholino against dysferlin leads to a decrease of endocytosis in oocytes, and to a developmental arrest during gastrulation. These results suggest that dysferlin is critical for normal endocytosis during oogenesis and for embryogenesis in the sea star and that this animal may be a useful model for studying the relationship of dysferlin structure as it relates to its function.     

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.     

Postprandial gastrointestinal blood flow, oxygen consumption and heart rate in rainbow trout (Oncorhynchus mykiss)

The present study is the first to simultaneously and continuously measure oxygen consumption (MO₂) and gastrointestinal blood flow (q_gi) in fish. In addition, while it is the first to compare the effects of three isoenergetic diets on q_gi in fish, no significant differences among diets were found for postprandial MO₂, q_gi or heart rate (f_H) in rainbow trout, Oncorhynchus mykiss. Postprandial q_gi, f_H and MO₂ were significantly elevated above baseline levels by 4 h. Postprandial q_gi peaked at 136% above baseline after 11 h, f_H peaked at 110% above baseline after 14 h and MO₂ peaked at 96% above baseline after 27 h. Moreover, postprandial MO₂ remained significantly elevated above baseline longer than q_gi (for 41 h and 30 h, respectively), perhaps because most of the increase in MO₂ associated with feeding is due to protein handling, a process that continues following the absorption of nutrients which is thought to be the primary reason for the elevation of q_gi. In addition to the positive relationships found between postprandial MO₂ and q_gi and between postprandial MO₂ and f_H, we discovered a novel relationship between postprandial q_gi and f_H.     

Response of the respiratory rate of Daphnia magna to changing food conditions

Summary The respiratory rate of the cladoceran Daphnia magna was measured at varying concentrations of a green alga in a flow-through respirometer. Daphnids were either preconditioned to the respective food concentration or the food concentration was suddenly changed during the experiment and the response of the respiratory rate monitored. Previously starved animals were provided with food or prefed animals were deprived of food. The respiratory rate increased considerably with increasing concentrations of algae until a maximum rate was reached at a critical algal concentration corresponding to the incipient limiting level for feeding. The response of the respiratory rate to changing food conditions was fast, lagging only a few minutes behind the change in food. The respiratory rate of starved daphnids increased quickly when they received food, even at low concentrations. Prefed daphnids responded to the replacement of the food suspension by filtered water with reductions in their respiratory rates. A linear relationship between the assimilation rate and the respiration rate was found, indicating that the more than twofold range of the respiratory rate was due to specific dynamic action. The SDA coefficients of 0.15–0.24 found for Daphnia are consistent with values for marine zooplankton.     

The relationship between specific dynamic action and growth in grass carp, Ctenophavyngodon idella (Val.)

Individual grass carp, Ctenopharyngodon idellu , were maintained in a respirometer for a month and fed pelleted diets containing various proportions of carbohydrate, fat and protein at different ration levels. Oxygen consumption was measured continuously, allowing the effects of consecutive daily feeding on respiration to be studied. The relationships established between daily food intake and oxygen consumption showed that, on average, 23.3% (high protein diet), 15.3% (high carbohydrate diet), 20.7% (high lipid diet) and 7.0% ( Lemnu diet ) of the absorbed energy was partitioned into specific dynamic action (SDA). (Here the term SDA is used to describe the oxygen consumption of a feeding fish in excess of the routine metabolic rate.) In terms of the overall energy budgets of growing fish, SDA represented between 12 and 58% of the total heat lost over the experimental period and was equivalent to between 14 and 33% of the consumed energy. Ration was positively correlated with heat loss due to total respiration ( r = 0.881) and with heat loss due to SDA ( r = 0.762). As ration increased, the size of SDA relative to total respiration increased. Significant positive correlations were found between oxygen consumption (total or due to SDA) and specific growth rate, and between oxygen consumption and the deposition of protein and energy. However, growth rate had a minimal influence on daily oxygen consumption when compared with food intake.     

An ultrastructural study of relationships between the ovarian haemal system,follicle cells,and primary oocytes in the sea star,Asterias rubens

Summary The genital haemal sinus, present throughout the gonad wall of sea stars, is supposed to be the site of ultimate accumulation of nutrients for the germinal epithelium. Early vitellogenic pear-shaped oocytes are attached to this sinus by stalk-like processes. The ultrastructure of this association and of the oocyte-follicle cell complex is described with emphasis on mechanisms involved in oocyte nutrition.The genital haemal sinus, and sometimes portions of the surrounding genital coelomic sinus, contain a fine granular ground substance and amoeboid cells. Material similar to the haemal ground substance also fills vacuities in the inner basal laminae of the haemal sinus and intervenes between this layer and adjacent germinal and follicle cells in the ovarian lumen.Vitellogenesis is first detectable as numerous vacuoles accumulate within the oocyte-stalk near the haemal sinus; they contain flocculent material and often fuse with adjacent lysosome-like vacuoles. As vitellogenesis proceeds, oocytes develop complex and tenuous connections with the haemal sinus. These consist of a network of pseudopodia that interdigitate with thin sheet-like extensions of follicle cells. These cells are attached to the oolemma by microfilamentous processes and contain regularly arranged concentrations of glycogen granules and well developed rough endoplasmic reticulum.It is concluded, (1) that follicle cells provide each oocyte with a compartmentalized microenvironment within the ovarian lumen, (2) that such compartments are intimately associated with the nutrient laden haemal sinus, and (3) that nutritive and vitellogenic substances, derived extragonadally and stored temporarily in the ovarian wall, can pass through the oocyte-stalk.     

Effects of feeding and hypoxia on cardiac performance and gastrointestinal blood flow during critical speed swimming in the sea bass Dicentrarchus labrax

Previous studies have shown that if European sea bass are exercised after feeding, they can achieve a significantly higher maximum metabolic rate (MMR) than when fasted. They can meet combined metabolic demands of digestion (specific dynamic action, SDA) and maximal aerobic exercise, with no decline in swimming performance. If, however, exposed to mild hypoxia (50% saturation), bass no longer achieve higher MMR after feeding but they swim as well fed as fasted, due to an apparent ability to defer the SDA response. This study explored patterns of cardiac output (Q_A) and blood flow to the gastrointestinal tract (Q_GI) associated with the higher MMR after feeding, and with the ability to prioritise swimming in hypoxia. Sea bass (mean mass ~ 325 g, forklength ~ 27 cm) were instrumented with flow probes to measure Q_A and Q_GI during an incremental critical swimming speed (U_crit) protocol in a tunnel respirometer, to compare each animal either fasted or 6 h after a meal of fish fillet equal to 3% body mass. Feeding raised oxygen uptake (M_O2) prior to exercise, an SDA response associated with increased Q_A (+ 30%) and Q_GI (+ 100%) compared to fasted values. As expected, when exercised the fed bass maintained the SDA load throughout the protocol and achieved 14% higher MMR than when fasted, and the same U_crit (~ 100 cm s^-1). Both fed and fasted bass showed pronounced increases in Q_A and decreases in Q_GI during exercise and the higher MMR of fed bass was not associated with higher maximum Q_A relative to when fasted, or to any differences in Q_GI at maximum Q_A. In hypoxia prior to exercise, metabolic and cardiac responses to feeding were similar compared to normoxia. Hypoxia caused an almost 60% reduction to MMR and 30% reduction to U_crit, but neither of these traits differed between fed or fasted bass. Despite hypoxic limitations to MMR and U_crit, maximum Q_A and patterns of Q_GI during exercise in fasted and fed bass were similar to normoxia. Estimating GI oxygen supply from Q_GI indicated that the ability of bass to prioritise aerobic exercise over SDA when metabolically limited by hypoxia was linked to an ability to defer elements of the SDA response occurring outside the GI tract.     

Changes in the digestive gland of the loliginid squid Sepioteuthis lessoniana (Lesson 1830) associated with feeding

Changes associated with feeding in the histological and cytological structure of the digestive gland of the loliginid squid Sepioteuthis lessoniana were examined, along with the nature of both the intracellular and extracellular enzymes produced by the gland. The timing of the release of the extracellular enzymes during the digestive cycle was also determined using a quantitative experimental program. Like that of all coleoid cephalopods, the digestive gland was characterised by one type of cell with several functional stages. As is the case for other loliginid squids, however, the digestive cells did not contain the large enzyme-carrying boules that characterise the digestive glands of most cephalopods. Instead, smaller secretory granules were found in the digestive cells and these may be the enzyme carriers. The prominent rough endoplasmic reticulum, large mitochondria and active Golgi complexes present in the digestive cells are characteristic of cephalopods and indicate a high metabolic activity. Like that of other cephalopods, endocytotic absorption of nutrients and intracellular digestion occurs in the digestive gland of this squid. From quantitative and qualitative examinations of structural changes in the digestive gland of S. lessoniana after feeding, a schedule of its function during the course of digestion was proposed. This indicated that digestion was very rapid, being completed in as little as 4 h in S. lessoniana. Extracellular digestive enzymes were only released after the first hour following feeding, which implies that they are stored in the stomach between meals to increase digestive efficiency.     

Influence of food density on respiration rate of two crustacean plankters,Daphnia galeata and Bosmina longirostris

Summary The influence of food density on respiration rate was measured for two cladoceran plankton species, Daphnia galeata and Bosmina longirostris, over the range 0 to 2.5 mg C 1^-1, using the modified Winkler technique in order to examine how this affects the respiration rate and whether the functional response is the same in the two species. The respiration rate for animals of equivalent body size did not differ significantly between the two species in the absence of food, but was significantly lower in Bosmina longirostris than Daphnia galeata at high food density. Within a species, the response of respiration rate to changing food density did not differ among individuals of different body size. The respiration rate of D. galeata increased with increasing food density and reached a plateau at a high food density. A similar response curve was also found with the respiration rate of B. longirostris, although the response was less conspicuous. This response curve cannot be explained by the energy cost of known feeding behavior in cladocerans. Since the respiration rate related linearly with the assimilation rate, increase in food density seemed to increase the respiration rate by increasing the energetic cost required to process food biochemically, known as specific dynamic action.     

Growth-inhibition effects of pacifastin-like peptides on a pest insect: the desert locust, Schistocerca gregaria

The main reason for the varying degrees of success of peptidase inhibitors (PI) as biological insecticides is the existence of a poorly understood mechanism, which allows pest insects to compensate for PI present in their diet. To challenge this highly flexible physiological mechanism and to prolong the inhibitory effect of PI on insect growth, a number of measures were taken into account before and during experiments with a notorious pest insect, the desert locust, Schistocerca gregaria: (i) non-plant PI (pacifastin-related inhibitors) were used to reduce the risk of a specific co-evolutionary adaptation of the pest insect, (ii) based on the main types of digestive enzymes present in the midgut, mixtures of multiple PI with different enzyme specificity were selected, allowing for a maximal inhibition of the proteolytic activity and (iii) digestive peptidase samples were taken during oral administration experiments to study compensatory mechanisms. Contrary to larvae fed on a diet containing plant-derived PI, a significant growth impediment was observed in larvae that were fed a mixture of different pacifastin-like PI. Nevertheless, the growth inhibition effect of this PI mixture attenuated after a few days, Moreover, a comprehensive study of the observed responses after oral administration of PI revealed that S. gregaria larvae can adjust their secreted digestive enzyme activities in two distinct ways depending on the composition/concentration of the PI-mixture.     

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 and postprandial thermophily in juvenile northern water snakes,Nerodia sipedon

1. We measured oxygen consumption of seven juvenile Northern water snakes, Nerodia sipedon, at 3, 19, 41, and 89 h after feeding. 2. Oxygen consumption 19 h after eating was significantly higher than at 3, 41, and 89 h after feeding and the values at 3 h post-feeding were significantly higher than those at 41 and 89 h. 3. We monitored substrate temperature preference in nine juvenile N. sipedon at 2000, 0000, 0800, 1200, and 1600 h for 3 days. 4. After feeding and at night snakes selected warmer substrate temperatures.