Gut morphology,feeding rate and gut clearance in five species of caddis larvae

Feeding rate, the rate of movement of food through the gut and gut morphology of large larvae of five caddis species (Halesus radiatus, Hydropsyche instabilis, Polycentropus kingi, Rhyacophila dorsalis and Potamophylax cingulatus) were investigated in the laboratory. Following 72 hr starvation, P. cingulatus and H. radiatus larvae became satiated (refused prey offered directly to the mouthparts) after consuming 8–11 and 9–13 mayfly nymphs (Baetis rhodani, 3.5–4.6 mm) respectively. Hunger level affected prey consumption. In P. cingulatus, the number of prey consumed over 24 h (at 9.5–12 °C) increased with starvation periods from 0–72 h, but declined following longer starvation periods. Six clearly recognisable gut states (defined by the position of food material in various parts of the gut) can be identified at different times since commencement of a meal. As environmental temperature increased (from 8–12 °C to 15–17 °C), the rate of change of the gut state increased and the food retention time decreased in all species. Feeding periodicity (i.e. nocturnal/diurnal activity) in the field was estimated based on the evacuation rate and the gut state and environmental temperature at the known time of collection. Initiation of consumption of prey appeared to coincide with emptying of the foregut and proximal midgut, whereas actual feeding continued until complete satiation when some threshold fullness of the foregut had been reached. The length of time food was held in the foregut was positively correlated with increasing specialisation of the foregut (particularly elaboration of the proventriculus).     

Rates of gastric evacuation in piscivorous brown trout, Salmo trutta

SUMMARY. 1. The dry weight of food remaining in the stomachs of piscivorous trout decreased exponentially with time. Gastric evacuation rates increased exponentially with increasing temperature but were unaffected by predator size, meal size or type of fish prey.
2. Mathematical models were developed to estimate both the rate and time for the gastric evacuation of different meal sizes (expressed as dry weight), and were applicable to piscivorous trout of different sizes (length range 10–32 cm) feeding on trout fry or sticklebacks at different temperatures (range 5–18°C).
3. The wet weight of food in the stomachs also decreased exponentially with time, but evacuation rates both increased with temperature and decreased with increasing meal size; the latter relationship occurred because relative rates of water loss from a meal also decreased with increasing meal size. Use of wet or dry weights can therefore lead to different conclusions about the effect of meal size on evacuation rates.
4. When piscivorous trout were fed three consecutive meals of varying size, the models predicted the total dry weight of food left in the stomach, but not the weight remaining for each individual meal. Interactions between meals led to an increase in evacuation rates for meals consumed early in the series and a decrease in evacuation rates for later meals.
5. Evacuation rates for piscivorous trout were compared with those for trout feeding on invertebrates in an earlier study, and were close to those for caddis larvae as prey, higher than those for mealworms and lower than those for a variety of invertebrate prey. Although a great deal is now known about the daily food intake and growth rates of trout feeding on invertebrates, there is little comparable information for piscivorous trout.     

Which components of diet quality affect retention time of digesta in seabirds?

1. The nature of the diet can affect the gut retention time of food consumed by an animal, and a theoretical framework has been developed to explain this in terms of optimal digestion rates. However, diets may differ in a number of different attributes, all of which may separately affect the optimal length of time that they are retained in the gut.
2. Here an attempt is made to elucidate which of these features are important in determining gut retention time of different fish species when fed to nine north Atlantic seabird species, and discuss the different potential optimization criteria for retention time in seabirds.
3. Retention times of Lesser Sandeel ( Ammodytes marinus Raitt.) were shortest, and this species was also rapidly broken down in vitro . Sprat ( Sprattus sprattus (L.)) took longer to be broken down in vitro than Whiting ( Merlangius merlangus (L.)), and also had a high energy and lipid content, which might be expected to result in slow digestion; yet retention times of the two species were similar.
4. Meal size also had an important effect on gut retention times, large meals being retained for longer in the gut than small meals, apparently because of an upper limit on the peak excretion rate.
5. Diet and meal-size related characteristics are important factors influencing prey profitability, prey selection and foraging patterns in seabirds.     

Physiological mechanisms underlying the control of meal size in Manduca sexta larvae

Abstract. Fifth stadium larvae of the tobacco hornworm, Manduca sexta (L.), ate larger meals than usual when they had been deprived of food for periods of time longer than the usual intermeal interval (c. 45 min). Meal size increased with time since the last meal until 180 min, when it was about 3 times normal. There was no evidence of a role for volumetric feedback from the gut in controlling meal size. Injections of a paraffin oil/wax mixture, or of petroleum jelly (Vaseline) into the foregut, midgut or rectum failed to decrease meal size. Cutting the recurrent nerve failed to alter meal size compared to sham-operated controls (although both groups took smaller meals than unoperated controls). By contrast, injections of an extract of soluble nutrients from the diet into the midgut inhibited feeding in some insects and reduced subsequent meal size in others. Appropriate controls showed that these effects were not due to the volumetric or osmotic effects of the injections. These results imply that nutrient feedback plays an important role in controlling meal size in Manduca caterpillars, while volumetric feedback is probably unimportant.     

The effect of deprivation on the microstructure of feeding by the Tobacco hornworm caterpillar

An automated device was used to examine, in detail, feeding on disks of wheat germ medium by fifth-instar Manduca sextacaterpillars. Comparisons were made between some animals which had ad libitum access to food at all times and others which were deprived of food for 1–5 h before being tested. Feeding patterns of both groups indicated regulation of feeding both between and within meals. Deprived animals ate more during their first meal than did nondeprived animals chiefly by increasing (a) the number of chewing bouts (and thus the meal duration) and (b) the bite frequency. Calculations indicated that the deficit caused by deprivation was made up during the first meal. However, deprived animals continued to eat more than nondeprived ones in subsequent feeding also. Passage of food through the gut was examined by dissecting out the contents of each region of the gut at various times after a colored test meal. Food passed through the foregut directly into the anterior part of the midgut. It stayed in the middle third of the midgut longer than in the anterior and posterior thirds, and the first pellet resulting from the test meal appeared 4 h after the meal. The following mechanisms of feeding regulation are proposed: (a) volumetric feedback mediated by stretch receptors of the foregut and anterior third of the midgut which terminates meals; (b) the development and subsequent reduction of satietyspecific behaviors mediated either by stretch receptors or by some other means which, e.g., allow the next meal to begin; and (c) metabolites whose levels drop during deprivation, triggering a series of events which lead to the excess feeding observed.     

Food capture, appetite, digestion rate and efficiency in hatchling and juvenile Crocodylus porosus

Juvenile estuarine crocodiles captured insects and crabs at or above the water surface by leaps and lunges powered by the hind limbs and tail. The mouth opened as the head cleared the water; most prey were held by sidesnaps of the jaws. Such prey capture was accurate, deliberate and preceded by stalking. In contrast, submerged prey (e.g. prawns) appeared to be detected mainly by touch and detection was followed by undirected, inaccurate 'snapping frenzies' which were usually ineffective. Small prey items were swallowed whole under water. Large dense prey (e.g. crabs) were handled and swallowed on land or in very shallow water; large less dense prey (e.g. cockroaches) were swallowed during vigorous water-treading in deep water, the head being maintained above the water surface.
Young crocodiles ate satiation meals of 9–10% body weight (on a fresh food weight basis) at 30°C, and appetite returned over about 40 h as the stomach emptied. Total gut clearance time for a meal was 4–5 d. Evidence was obtained which demonstrated that young Crocodylus porosus Schneider deliberately eat gastroliths from an early stage. Such gastroliths are retained within the stomach (as were barium/polystyrene spheroids of 1 mm diameter) presumably by the action of the well-developed pyloric sphincter. X-radiographs demonstrated that gastroliths are dispersed throughout the stomach contents after a meal and presumably aid digestion.
Assimilation rates for dry mass (77.5%), energy (85.2%) and protein-N (97.4%) were high in normal juveniles. Animals exhibiting 'runt syndrome' showed strong appetite but slow food processing by the gut, together with poor assimilation, especially of protein (35.7%).     

A review of gastric processing in decapod crustaceans

This article reviews the mechanical processes associated with digestion in decapod crustaceans. The decapod crustacean gut is essentially an internal tube that is divided into three functional areas, the foregut, midgut, and hindgut. The foregut houses the gastric mill apparatus which functions in mastication (cutting and grinding) of the ingested food. The processed food passes into the pyloric region of the foregut which controls movement of digesta into the midgut region and hepatopancreas where intracellular digestion takes place. The movements of the foregut muscles and gastric mill are controlled via nerves from the stomatogastric ganglion. Contraction rates of the gastric mill and foregut muscles can be influenced by environmental factors such as salinity, temperature, and oxygen levels. Gut contraction rates depend on the magnitude of the environmental perturbation and the physiological ability of each species. The subsequent transit of the digesta from the foregut into the midgut and through the hindgut has been followed in a wide variety of crustaceans. Transit rates are commonly used as a measure of food processing rates and are keys in understanding strategies of adaptation to trophic conditions. Transit times vary from as little as 30 min in small copepods to over 150 h in larger lobsters. Transit times can be influenced by the size and the type of the meal, the size and activity level of an animal and changes in environmental temperature, salinity and oxygen tension. Ultimately, changes in transit times influence digestive efficiency (the amount of nutrients absorbed across the gut wall). Digestive efficiencies tend to be high for carnivorous crustaceans, but somewhat lower for those that consume plant material. A slowing of the transit rate allows more time for nutrient absorption but this may be confounded by changes in the environment, which may reduce the energy available for active transport processes. Given the large number of articles already published on the stomatogastric ganglion and its control mechanisms, this area will continue to be of interest to scientists. There is also a push towards studying animals in a more natural environment or even in the field and investigation of the energetic costs of the components of digestion under varying biotic and environmental conditions will undoubtedly be an area that expands in the future.     

Characterization of four esterase genes and esterase activity from the gut of the termite Reticulitermes flavipes

Four esterase genes and general esterase activity were investigated in the gut of the termite Reticulitermes flavipes. Two genes (RfEst1 and RfEst2) share significant translated identity with a number of insect JH esterases. The two remaining genes (RfEst3 and RfEst4) apparently code for much shorter proteins with similarity to fungal phenolic acid esterases involved in hemicellulose solubilization. All four genes showed consistently high midgut expression. This result was further supported by colorimetric activity assays and Native polyacrylamide gel electrophoresis, which showed significant esterase activity and a number of isoforms in the midgut. The greatest esterase activity and isoform composition were detected when α‐naphthyl propionate was used as a substrate. Moreover, esterase activity and diverse isoforms were present in gut mitochondrial, microsomal, and cytosolic sub‐cellular protein fractions, as well as in the hindgut lumen. These findings reveal an agreement between gut esterase gene expression and activity distributions, and support the idea that R. flavipes gut esterase activity is host (not symbiont)‐derived. In addition, these findings support the hypotheses that termite gut esterases may play important roles in lignocellulose digestion and caste differentiation. This study provides important baseline data that will assist ongoing functional‐genomic efforts to identify novel genes with roles in semiochemical, hormone, and lignocellulose processing in the termite gut. © 2009 Wiley Periodicals, Inc.     

Mucous contribution to gut nutrient content in American gizzard shad Dorosoma cepedianum

This study developed and applied an approach to calculate the proportion of fish gut content composed of mucus secreted by the oropharyngeal cavity and gut. The amount of nitrogen in the contents of the foregut (oesophagus and gizzard) and the epibranchial organs of suspension‐feeding American gizzard shad Dorosoma cepedianum was significantly higher than the nitrogen in the homogeneous food source. Using data collected from suspension‐feeding experiments and the nitrogen content of D. cepedianum mucus, a series of equations illustrated that mucus constituted c. 10% of D. cepedianum foregut content and 12% of epibranchial organ content by dry mass. Future quantification of fish feeding selectivity and absorption efficiency can use this approach to take into account the contribution of fish mucus to the nutrients in the gut contents. This study supports the conclusion that suspension‐feeding D. cepedianum in a heterogeneous environment selectively ingest nutrient‐rich particles, even when gut nutrient content is adjusted to take into account the contribution of mucus.     

Reduced feeding during water deprivation depends on hydration of the gut

Removal of drinking water at the start of the dark period reduced food intake in freely feeding rats within 45 min. Both first and later meals were smaller during 7.5 h of water deprivation, but meal frequency did not change. Ingestion of a normal-sized meal (3 g) rapidly increased plasma tonicity when drinking water was withheld, but intravenous infusions of hypertonic NaCl causing similar increases in plasma tonicity did not reduce feeding. Feeding during 6 h of water deprivation was restored by slowly infusing the volume of water normally drunk into the stomach, jejunum, or cecum, but not in the vena cava or hepatic portal vein. The infusions did not alter water or electrolyte excretion or affect food intake in rats allowed to drink. We conclude that the inhibition of feeding seen during water deprivation is mediated by a sensor that is located in the gastrointestinal tract or perhaps in the mesenteric veins draining the gut, but not the hepatic portal vein or the liver. In the absence of drinking water, signals from this sensor provoke the early termination of a meal.     

Optimal foraging and gut constraints: reconciling two schools of thought

To ecologists, factors such as a forager's encounter rate with prey and its own susceptibility to predation are dominant determinants of foraging. In contrast, digestive physiologists consider foraging to be determined by factors like rates of digestion and absorption of ingested food. We reconcile these views in a model combining encounter rate, external handling, and internal handling of food in the gut. With internal food handling, two food properties become important; energy: external handling time (e/h) and energy: bulk (e/b). We show that internal handling is only one of a suite of rate limiting factors. The gut never reaches full capacity, indicating that spare capacity may be intrinsic to gut structure. Regardless of gut fullness, a food of sufficiently high e/b will always be harvested. Two isolegs in the state space of resource abundances determine diet selectivity. These isolegs, which we call the Mitchell and Pulliam isolegs, divide the state space into regions in which 1) the forager's optimal strategy is opportunism; 2) the forager is always selective on the food with the greater e/h and partially selective on the second food; 3) the forager is always selective on the food with the greater e/h and ignores the second food. The development and analysis of the isolegs thus reconcile the heretofore disparate perspectives of the ecological and the physiological frameworks of foraging.     

The energetics of coprophagy: a theoretical analysis

Lagomorphs, many rodents and some other small mammals eat their faeces during the part of the day when they are not foraging for fresh food. One of the possible benefits of this habit of coprophagy is that it may enable them to extract more energy from their food. A computer model is used to assess the likely benefits and explore their relationships to food, feeding rate and gut morphology. The predicted benefits are much larger for hindgut fermenters than for foregut fermenters, and especially large for hindgut fermenters with relatively small fermentation chambers. They are larger for poor foods (with lower proportions of cell contents) than for richer ones. At low feeding rates the energetic advantage of coprophagy may disappear if the faeces from food eaten during one feeding period emerge largely during the next, but this can be avoided by adjusting the rate of passage of gut contents during the intervening rest period.     

Immunofluorescence assay for effects on field abundance of a naturally occurring pseudomonad during passage through the gut of a marine deposit feeder,Abarenicola pacifica

In a seasonal study we used immunofluorescence to follow a specific bacterial population, as well as total numbers, through the fore-, mid-, and hindgut of a deposit feeder, Abarenicola pacifica. We chose a pseudomonad because of its high ambient abundance. On five dates, we collected A. pacifica gut contents, with concurrent measurements of sedimentary food quality (chlorophyll a, protein, bacterial abundance), animal egestion rates (inversely proportional to gut residence time), and temperature. Increasing bacterial numbers from ingested sediment to foregut contents, and decreases from foregut to midgut indicate significant selection and digestion, respectively, of both the pseudomonad and the total bacterial community. Inverse correlations between egestion rate and digestive removal of bacteria offer some support for the prediction that digestion of bacteria is proportional to time spent exposed to digestive enzymes, although the significance of the associated statistical tests is marginal. No hindgut growth of the pseudomonad was observed, likely due to the short gut residence time of A. pacifica. The pseudomonad showed variation of less than a factor of 3 in its ambient sedimentary abundance over the year. Off print requests to: C. Plante.     

Factors affecting detectability of prey DNA in the gut contents of invertebrate predators: a polymerase chain reaction-based method

This study aimed to determine factors that influence the detection of DNA of Plutella xylostella L. (Lepidoptera: Plutellidae) in the gut contents of arthropod predators when the polymerase chain reaction is used to amplify a diagnostic fragment of the gene coding for cytochrome oxidase subunit I. The effects of temperature, time since feeding, subsequent food intake, sex, weight, and species of predator on prey detectability were studied in the laboratory. Three types of predator were studied: the spider Venator spenceri Hogg. (Araneae: Lycosidae), a bug with sucking mouthparts, Nabis kinbergii (Reuter) (Heteroptera: Nabidae), and a coccinellid with chewing mouthparts, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae). In all experiments, the detectability of prey DNA was negatively correlated with time post‐feeding. The duration of detectability differed among the predator species. The time calculated for median detection success at 20 °C ranged from 49.6 h in V. spenceri to 36.1 h in N. kinbergii and 17.1 h in H. variegata. In H. variegata, but not in V. spenceri, the rate of detection decreased with increasing temperature. Subsequent food intake did not affect the detectability of DNA of P. xylostella in V. spenceri. In H. variegata, sex and weight of the predator did not influence detection of prey DNA. In addition, this study uncovered potential sources of error caused by detection of prey DNA following secondary cannibalistic and intraguild predation. The results provide essential information for the interpretation of prey detection data from field‐collected predators’ gut contents.     

扩头蔡白蚁肠道蛋白的鉴定

【目的】本研究旨在分析比较扩头蔡白蚁Tsaitermes ampliceps工蚁前中肠和后肠及其内容物的蛋白构成和表达差异,挖掘降解木质纤维素的相关酶和蛋白。【方法】通过扩头蔡白蚁工蚁的前中肠和后肠及其内容物蛋白的双向电泳,对高表达或高差异表达的47个蛋白点进行MALDI-TOF/MS测序,并进行生物信息学分析。【结果】测序分析发现,扩头蔡白蚁肠道及其内容物蛋白中有结构蛋白13个、调节蛋白9个、白蚁代谢相关蛋白10个、微生物代谢相关蛋白7个。经PD Quest分析发现,在前中肠和后肠有11个蛋白均高表达;仅在前中肠表达的蛋白有12个,主要是白蚁代谢相关蛋白和调节蛋白;仅在后肠表达的蛋白有8个,主要是微生物代谢相关蛋白。整个肠道内参与木质纤维素降解的相关酶有5个,分别是白蚁自身分泌的内源性纤维素酶,细菌产生的内切-β-1,4-葡聚糖酶和过氧化物歧化酶以及原生动物产生的GH11。【结论】白蚁对木质纤维素食物的降解主要在前中肠,后肠对降解产物进一步降解并进行微生物生长代谢。这些降解产物和微生物菌体蛋白为白蚁的肛哺提供营养成分。     

The estimation of crop evacuation rates in Chaoborus larvae (Diptera: Chaoboridae) using natural prey

SUMMARY. 1. Crop evacuation rates were estimated for the first time in Chaoborus larvae, using natural prey.
2. Fourth instar C. americanus Matheson digested copepods (Diaptomus leptopus S.A. Forbes) 48.7% faster than daphnids (Daphnia rosea Leydig) of similar size; meal size did not significantly affect the instantaneous rate of digestion (IRD) within each prey type. Prey specific IRD has not been reported before for zooplankton.
3. Prey specific differences in IRD require the use of natural prey when digestion experiments are to be used to estimate natural rates of food consumption of animals.     

Size-dependent flight initiation by a lotic mayfly in response to a predatory fish

1. Laboratory experiments were performed to determine whether flight initiation by lotic mayfly larvae of Baetis tricaudatus exposed to the longnose dace ( Rhinichthys cataractae ) is affected by an individual's size and its physiological state.
2. We used a three factorial ANOVA design to test whether flight initiation distances (FIDs) were affected by Baetis size (small, large), starvation level (low, high), and the length of a predator-free foraging period (short, long).
3. FIDs were significantly affected by the interaction between Baetis size and starvation level, and the main level effects of starvation and Baetis size. FIDs of small larvae were unaffected by starvation level and the length of the predator-free feeding period, whereas starvation reduced FIDs of large larvae 2-fold.
4. Subsequent experiments showed that size-dependent differences in FIDs could not be attributed to size-specific differences in the economics of rates of food intake or gut evacuation. For both small and large larvae, food intake rates declined with increasing time spent foraging and both small and large larvae consumed the majority (70–75%) of food within the first 3 h of the 12-h feeding period. Similarly, gut evacuation declined with increasing starvation time and rates of evacuation did not differ between small and large larvae. These data suggest that size-dependent differences in flight initiation by Baetis larvae do not involve the energetics of food intake or processing.     

Size-dependent flight initiation by a lotic mayfly in response to a predatory fish

1. Laboratory experiments were performed to determine whether flight initiation by lotic mayfly larvae of Baetis tricaudatus exposed to the longnose dace ( Rhinichthys cataractae ) is affected by an individual's size and its physiological state.
2. We used a three factorial ANOVA design to test whether flight initiation distances (FIDs) were affected by Baetis size (small, large), starvation level (low, high), and the length of a predator-free foraging period (short, long).
3. FIDs were significantly affected by the interaction between Baetis size and starvation level, and the main level effects of starvation and Baetis size. FIDs of small larvae were unaffected by starvation level and the length of the predator-free feeding period, whereas starvation reduced FIDs of large larvae 2-fold.
4. Subsequent experiments showed that size-dependent differences in FIDs could not be attributed to size-specific differences in the economics of rates of food intake or gut evacuation. For both small and large larvae, food intake rates declined with increasing time spent foraging and both small and large larvae consumed the majority (70–75%) of food within the first 3 h of the 12-h feeding period. Similarly, gut evacuation declined with increasing starvation time and rates of evacuation did not differ between small and large larvae. These data suggest that size-dependent differences in flight initiation by Baetis larvae do not involve the energetics of food intake or processing.     

Satiation,digestive tract evacuation and return of appetite in the European minnow,Phoxinus phoxinus (Cyprinidae) following short periods of pre-prandial starvation

Synopsis In adultPhoxinus phoxinus (Cyprinidae), starvation for 4 or 16 days had no significant effect on the rate of foregut evacuation of the first satiation meal consumed after the starvation period. Starvation for 4 and 16 days had no significant effect on the rate of return of appetite after that first meal. A model based on the rates of foregut evacuation and return of appetite predicted that in the presence of excess food, the foregut contents would represent about 4% of total body weight. This prediction was corroborated experimentally. The effect of the length of starvation on the size of the first meal was not consistent. The results suggest that the hyperphagia noted in minnows starved for 16 days is a consequence of the persistence on succeeding days of the rates of evacuation and return of appetite achieved on the first day of realimentation.     

The influence of meal size on prey DNA detectability in piscivorous birds

Molecular methods allow noninvasive assessment of vertebrate predator–prey systems at high taxonomic resolution by examining dietary samples such as faeces and pellets. To facilitate the interpretation of field‐derived data, feeding trials, investigating the impacts of biological, methodological and environmental factors on prey DNA detection, have been conducted. The effect of meal size, however, has not yet been explicitly considered for vertebrate consumers. Moreover, different noninvasively obtained sample types remain to be compared in such experiments. Here, we present a feeding trial on abundant piscivorous birds, Great Cormorants (Phalacrocorax carbo), to assess meal size effects on postfeeding prey DNA detection success. Faeces and pellets were sampled twice a day after the feed of large (350–540 g), medium (190–345 g) and small (15–170 g) fish meals contributing either a large (>79%) or small (<38%) share to the daily consumption. Samples were examined for prey DNA and fish hard parts. Molecular analysis of faeces revealed that both large meal size and share had a significantly positive effect on prey DNA detection rate postfeeding. Furthermore, large meals were detectable for a significantly longer time span with a detection limit at ~76 hr and a 50% detection probability at ~32 hr postfeeding. In pellets, molecular methods reliably identified the meal consumed the previous day, which was not possible via morphological analysis or when examining individual faeces. The less reliable prey DNA detection of small meals or meal shares in faeces signifies the importance of large numbers of dietary samples to obtain reliable trophic data.