The feeding apparatus of a chitinivorous ciliate

The chitinivorous ciliate Ascophrys, an ectosymbiont of the shrimp Palaemon serratus, is enclosed by a thick cyst wall except for a ventral hiatus exposing a circular area of exoskeleton to the interior of the cyst. The exoskeleton underlying the cyst wall remains intact, but the circular area of exoskeleton is dissolved enzymatically and ingested. The feeding ciliate forms a cavity in the exoskeleton into which it sinks. Its complex oral apparatus resembles a pump encircled by cytoplasm containing Golgi and high concentrations of coated vesicles that join pellicular pores between cilia. The ingestive apparatus is formed of microtubular lamellae that originate in the midplane of the body, descend toward a coated membrane on the surface, and ascend again as a lamellar lining to a complex food tube that ends in the middle of the body surrounded by food vacuoles. The cytoplasm enclosed between the descending lamellae and the food tube is crowded with membrane organelles that recycle as food vacuole membranes at the coated membrane. We hypothesize that vacuoles containing dissolved exoskeleton are drawn up into the oral tube and are released into the cytoplasm at the terminus of the tube, where their contents are concentrated and excess vacuolar membrane collapsed into membrane organelles.     

Behavioral Energetics of Lactation in a Herbivorous Carnivore,the Red Panda (Ailurus fulgens)

In most mammals, the energetic costs of lactation significantly increase a female's daily energy requirements. Previous research indicates that such energetic costs may be met through changes in increased food consumption ranging from around 35 % to 150 %. In this paper, changes in food intake during lactation are measured in the red panda (Ailurus fulgens), a species of the order Carnivora which possesses a digestive system suited for a carnivorous diet but yet exclusively feeds on bamboo. Four feeding characteristics were studied: duration of feeding bouts, number of bamboo leaves consumed per mouthful, number of bamboo leaves consumed per minute, and interval between mouthfuls of bamboo. In three lactating females, three of four feeding behaviors significantly increased up to 200 % above the rate observed during non-lactation. Males showed no change in feeding behavior during the same reproductive months with identical available foods. Red pandas appear to suffer a more severe energetic cost during lactation (at least with respect to food consumption) than other mammals previously studied. This may relate to their inefficient digestive capacity to process a herbivorous diet of bamboo. The data presented here suggest that general discussions of the relative costs of reproduction and in turn parental investment should include a female's relative digestive efficiency during stressful reproductive periods.     

Behavioral Modes Arise From a Random Process in the Nudibranch Melibe

Stochastic analysis was applied to observations of spontaneous behavior in the carnivorous mollusc Melibe leonina. Six behaviors were denned that could be easily recognized on inspection and it was found that transitions between each of these behaviors could be fully described by a first-order random process without memory of past behavioral choices. The behaviors are organized by frequency of transition into two modes, a feeding mode and a resting mode. Transitions within modes are more likely than transitions between modes, and the feeding and resting modes are linked by a preferred pair of behavioral transitions. The amount of time spent in the feeding mode is positively correlated with body size, but the average length of a feeding episode is independent of size. This suggests that body size regulates the probability of entry into feeding behavior but does not influence the basic pattern of feeding. In the presence of food the animals express nearly continuous feeding behavior, suggesting that food reduces the probability of exiting the feeding mode. This model of spontaneous behavior in Melibe is used to form hypotheses amenable to further exploration through neurophysiological experiments.     

Abundance and Community Structure of Picoplankton and Protists in the Microbial Food Web of Barguzin Bay,Lake Baikal

We examined the vertical abundance of bacteria, phytoplankton and protists along a transect of six stations from near-shore (Stn. 1) to off-shore (Stn. 6) in Barguzin Bay of Lake Baikal, in the summer of 2002. Chlorophyll concentrations at Stn. 1 were higher (>10μg l⁻¹) than at the other five stations (<3μg l⁻¹). Planktonic and sessile diatoms dominated at Stn. 1, while pico-phytoplankon was dominant at other stations. Densities of heterotrophic bacteria were high in both the epilimnion and the thermocline at all stations. Nanoflagellates were abundant in the epilimnion, and ciliates in the thermocline, but no horizontal trend could be found for these heterotrophs. At Stn. 1, not only filter feeding (Strombidium and Strobilidium) and raptorial (Balanion) ciliates but also predatory ciliates (Prorodon and Spathidiosus) dominated, while at other stations only the filter feeding and raptorial ciliates were dominant. In off-shore stations (Stns. 5 and 6), significant correlations were detected between concentrations of chlorophyll a and density of filter feeding or raptorial ciliates, suggesting tight food linkages between phytoplankton and these ciliates. The concentration of dissolved organic carbon (DOC) was significantly correlated with chlorophyll a concentration, although there was no significant correlation between DOC concentration and bacterial density. We suggest that there is a shift of the dominant food linkage from a herbivorous food chain in near-shore areas to a microbial food web in off-shore areas in Barguzin Bay of Lake Baikal.     

Digestive and feeding characteristics of the chondrosteans

Synopsis Structure and function of the digestive system and feeding characteristics of the chondrosteans are reviewed. Although the group exhibits a wide diversity of feeding habits including piscivory, benthophagy, and planktivory, they are principally carnivores throughout their life history. Examination of digestive system structure reveals the basic structure to be similar among the species with some modification to accomodate the different food types. For the species studied, composition of the adult digestive enzyme complement is consistent with the carnivorous habits with proteases dominating and only low levels of carbohydrase activity. There are three secretory phases during development of the digestive system. Each corresponds with different food habits of the different life-history intervals. Vision is apparently not utilized for feeding in any interval. Instead food is recognized and located primarily by gustation, olfaction, textural qualities, and, possibly, electroreception.     

Vacuolar pH is one factor that regulates hydrolase secretion

Lysosomal hydrolases are continually secreted by Acanthamoeba as a consequence of membrane cycling between the vacuolar compartment and the cell surface. In pinocytosing amoebae acid hydrolases can be separated into two groups on the basis of their secretion kinetics. We have previously shown that in Acanthamoeba acid hydrolases are almost exclusively restricted to a single compartment, digestive vacuoles, and that pH-dependent differential binding of hydrolases to vacuolar membrane can account for the different rates of hydrolase secretion from this compartment. In this report we show that the hydrolase secretion pattern changes and that all of the hydrolases are released with the same kinetics after phagocytosis of yeast or in growth media supplemented with ammonium acetate or chloroquine, but not after phagocytosis of polystyrene beads. The changes in the pattern of hydrolase secretion correlate with changes in vacuolar pH. The vacuolar pH of pinocytosing amoebae and amoebae saturated with beads is about 4.8. This value is increased to 6.8 by accumulation of weak bases and to about 6.1 when digestive vacuoles are saturated with yeast. These results indicate that vacuolar pH modulates hydrolase transport and secretion.     

Effects of Chloroquine on the Feeding Mechanism of the Intraerythrocytic Human Malarial Parasite Plasmodium falciparum1

Ultrastructural investigations of P. falciparum cultivated in vitro in human erythrocytes revealed new features of the feeding mechanism of the parasite. Mature trophozoites and schizonts take up a portion of the host cytosol by endocytosis which is restricted to cytostomes and which involves the invagination of both parasitophorous and parasite membranes. The resulting endocytic vesicles, surrounded by two concentric membranes, migrate towards the central food vacuole membrane. The external membrane of the endocytic vesicles apposes that of the food vacuole, leading to the internalization of vesicles bounded by a single membrane into the vacuolar space where they are rapidly degraded. We conclude from this sequence of events that endocytic vesicles fuse with the food vacuole. Treatment of infected cells with therapeutic concentrations of chloroquine inhibited the last step of the feeding process, i.e. vacuolar degradation. This was manifested by the accumulation within the vacuolar space of intact vesicles bounded by single membranes. The implications of these findings for the antimalarial activity of chloroquine are discussed.     

Does diet variation determine the digestive tract length of Capoeta banarescui Turan,Kottelat, Ekmekci and Imamoglu, 2006?

This study tested the spatial variations in the digestive/intestine tract length of Capoeta banarescui, with regard to their diets in different habitats. Highly varied diets observed in a previous study within the same river system posed the question whether this flexibility is reflected in the digestive tract and intestine length of the species in the Ye?il?rmak River, Turkey. Totals of 382 specimens (standard length 4.6–19.1 cm) were captured by electro‐fishing along the river in September 2012 at 11 locations spanning elevations from 34 to 992 m. The stomach, intestine and total digestive tract lengths were measured, and stomach contents analysed from 196 specimens. For statistical analyses, the stomach, intestine and total digestive tract length were expressed as percentages of total weight and standard length. The data provided evidence that the digestive tract and intestine lengths varied significantly among locations in association with the diet. Fish having dominantly carnivorous diets (e.g. chironomid larvae/invertebrates) in two locations had significantly shorter intestines and digestive tracts than those with diets dominated by benthic algae and other plants. The data indicated that C. banarescui showed broad flexibility in their feeding habits. Feeding heavily on plant materials might lead to the development of longer digestive tracts, increasing the active surface area for digestion; alternatively, there may be less invested in development of the digestive tract when feeding primarily on carnivorous diets where the respective digestive enzymes are readily available. The data suggest that phenotypic plasticity in the digestive tract length of C. banarescui is associated more with the abundant protein‐rich carnivorous food sources in the studied habitats. Whether this digestive tract plasticity has a genetic background remains to be verified in future studies.     

Effects of chloroquine on the feeding mechanism of the intraerythrocytic human malarial parasite Plasmodium falciparum

Ultrastructural investigations of P. falciparum cultivated in vitro in human erythrocytes revealed new features of the feeding mechanism of the parasite. Mature trophozoites and schizonts take up a portion of the host cytosol by endocytosis which is restricted to cytostomes and which involves the invagination of both parasitophorous and parasite membranes. The resulting endocytic vesicles, surrounded by two concentric membranes, migrate towards the central food vacuole membrane. The external membrane of the endocytic vesicles apposes that of the food vacuole, leading to the internalization of vesicles bounded by a single membrane into the vacuole space where they are rapidly degraded. We conclude from this sequence of events that endocytic vesicles fuse with the food vacuole. Treatment of infected cells with therapeutic concentrations of chloroquine inhibited the last step of the feeding process, i.e. vacuolar degradation. This was manifested by the accumulation within the vacuolar space of intact vesicles bounded by single membranes. The implications of these findings for the antimalarial activity of chloroquine are discussed.     

Avian daily foraging patterns: Effects of digestive constraints and variability

Summary Birds show a typical daily pattern of heavy morning and secondary afternoon feeding. We investigate the pattern of foraging by a bird that results in the lowest long-term rate of mortality. We assume the following: mortality is the sum of starvation and predation. The bird is characterized by two state variables, its energy reserves and the amount of food in its stomach. Starvation occurs during the day if the bird's reserves fall to zero. The bird starves during the night if the total energy stored in reserves and the stomach is less than a critical amount. The probability that the bird is killed by a predator is higher if the bird is foraging than if it is resting. Furthermore, the predation risk while foraging increases with the bird's mass. From these assumptions, we use dynamic programming techniques to find the daily foraging routine that minimizes mortality. The principal results are (1) Variability in food finding leads to routines with feeding concentrated early in the day, (2) digestive constraints cause feeding to be spread more evenly through the day, (3) even under fairly severe digestive constraints, the stomach is generally not full and (4) optimal fat reserve levels are higher in more variable environments and under digestive constraints. This model suggests that the characteristic daily feeding pattern of small birds is not due to digestive constraints but is greatly influenced by environmental variability.     

食物在贻贝棘尾虫(原生动物,纤毛虫)细胞内的消化过程

利用免疫荧光显微术、透射电镜及电镜酶细胞化学技术对食物在腹毛类纤毛虫-- 贻贝棘尾虫细胞内的消化过程进行了追踪观察.食物在进入消化腔隙的初期,外面包被着一层膜结构,但此外层膜很快被消化而消失;尔后食物在贻贝棘尾虫体内的消化过程可分为两种方式:一种方式为直接在消化腔隙内完成,此过程同1982年Kaul et al.和Das s et al.的报道;而另一部分食物的消化过程表现为食物逐步向细胞质内突入,以致最终完全被细胞质包围形成一被膜包裹的圆泡状结构;在此过程中,细胞质边缘突出众多含有酸性磷酸酶等物质的小囊泡结构,小囊泡与食物融合,其内的酸性磷酸酶等水解酶释放出来, 食物的表膜逐渐瓦解,个体逐渐变小,最终消化后的营养物质被释放到细胞的消化腔隙内; 这种食物通过胞口与胞咽达消化腔隙后,再由细胞质将其包裹形成的食物泡,我们称之为" 后成食物泡".这两种消化方式与贻贝棘尾虫的消化胞器为一腔隙结构相适应[动物学报 5 4(3):510-516,2008].     

Effects of Food Availability and Predation on a Marine Zooplankton Community — a Study on Copepods in the Baltic Sea

The importance of food resources versus predatory effects in determining the abundance pattern of zooplankton varies over time and space. Here, we evaluate the population dynamics of dominant calanoid copepods (Acartia spp. bifilosa/A. longiremis and Eurytemora affinis) in a reference area and a eutrophied area in the northern Baltic Sea Proper. We base the paper on a combination of statistical analyses of a long term (12 years) data set on population biomass dynamics, laboratory experiments on the feeding biology of these species and literature data of their susceptibility to predation. Overall, copepods were equally abundant at both sites, but Eurytemora was more abundant in the eutrophied area while Acartia spp. dominated in the non-eutrophied reference area. There was, however, no significant difference between the two areas in biomass dynamics (biomass specific rate of change) of the two groups of copepods. However, in spring and early summer the population biomass increased faster for Eurytemora as compared to Acartia spp. This is consistent with our findings from feeding and respiration experiments. Eurytemora exhibited generally higher ingestion rates and had a higher growth efficiency (ratio of ingestion to respiration rates), which suggests an advantage over Acartia spp. when food availability increases. Both species generally showed a rapid population decline starting in late summer, most likely caused by intensive predation by fish and mysid shrimps. In late autumn and winter, biomasses of both genera continued to decrease, but the decline was fastest for Eurytemora. During this period of the year, when the food availability is sparse, Acartia spp. may have an advantage over Eurytemora, as we found that the former ingests a broader size range of food particles and it has also been reported to be able to switch from filter feeding to raptorial feeding. This study shows that dominant copepods in the net-zooplankton community in our study area were structured both by food availability and predation. The relative importance of these effects varied seasonally.     

Development of digestive secretions in white sturgeon juveniles (Acipenser transmontanus)

Development of the digestive enzyme complement corresponded with this species' carnivorous habits and a natural dietary shift at metamorphosis from larval pelagic zooplanktivory to benthic carnivory. During the first developmental stanza when the digestive tract was differentiating and the larvae were dependent on endogenous nutritional reserves, digestive enzyme concentrations were low. Initiation of gastric secretion (pepsin and acid) was concomitant with onset of exogenous feeding. Highest amylolytic and lipolytic activities were recorded from feeding larvae prior to their metamorphosis to juveniles.     

Regulation of diurnal filter feeding by a novel gill structure in Amblypharyngodon melettinus (Teleostei,Cyprinidae)

A unique gill structure, apparently associated with filter feeding on phytoplankton and suspended microdetritus, has been found in Amblypharyngodon melettinus, an abundant small Cyprinidae of Sri Lanka. The gill lamellae, the site of gas exchange, are bordered by a double row of fine appendices which are spread over the interlamellar gaps during daytime, but folded up at night. A respiratory function of the appendices can be excluded. The changing position of appendices correlates with the diurnal pattern of feeding (day) and swimming (night). The mechanism for movement of the appendices consists of hinge-like joints formed from the basement membranes of pavement cells, driven by variation in lamellar blood pressure. Food collection is based on both an efficient hydrosol filter produced by dense populations of clavate mucous cells of the buccopharyngeal epithelia and the lamellar appendices which cause a slower and more turbulent water current in the buccopharyngeal cavity. This may ensure the proper contact of food particles with the sticky mucous surface before they leave the buccopharyngeal cavity. The uniqueness of this structure is that the filter can be switched off during periodically occurring periods of high oxygen demand (high swimming activity at night) probably benefiting the process of respiration.     

Feeding and digestion in two intertidal gammarids: Marinogammarus obtusatus and M. pirloti

The diet of two intertidal species of gammarid, Marinogammarus obtusatus Dahl and M. pirloti Sexton and Spooner is described. Both species feed largely, but not exclusively, on decaying algae, but may eat some living algae and, more rarely, carrion.
Their feeding activities are influenced by the rhythmic pattern of tidal ebb and flow, feeding only when covered by water. When immersed by the incoming tide they ingest food rapidly for a while and then feed more intermittently, ingesting small amounts at a time until they are uncovered once more by the receding tide. They probably eat sufficient food to fill the gut twice in 24 hours. The optimum rate for the digestion of food is approximately five hours, although food remains in the gut for about 12 hours.
The pH of the contents of the proventriculus, digestive gland and intestine of M. obtusatus is distinctly acid. Digestive enzymes are secreted only by the digestive gland. Carbohydrases are present which will hydrolyse soluble starch, glycogen, sucrose, maltose, arbutin, salicin, raffinose and melibiose. Inulin, lactose and cellulose are not hydrolysed. Non-specific esterase and true lipase were detected by histochemical methods.
It is concluded that the food supply available to these animals is plentiful and it is unnecessary to utilize the food supply to the maximum.     

Diet changes in prey size selectivity in larvae of perch <Emphasis Type="Italic">Perca fluviatilis</Emphasis>

A hypothesis on change in prey size selectivity in relation to illumination level was tested on the basis of data on weight and size composition of the content of the digestive tract of larvae of perch Perca fluviatilis and on zooplankton in the layer 0–6 m (Wallersee Lake, Austria). Larvae foraging in the twilight-night period had almost two times more food in the intestine than those foraging in the daytime. The size composition of perch larvae and concentration and size composition of zooplankton hardly differed in the daytime and twilight-night samples. For the first time, it is shown on field material that more intensive feeding of larvae at twilight is related to selection of significantly larger prey than in daytime feeding. In the day-time, the larvae consumed more prey but their maximum size did not exceed 0.6 of the diameter of mouth opening of the fish; at twilight it was over 0.8. In case of feeding on so large prey, not only the weight of the consumed feed increases but the time used for capture and swallowing also considerably increases. The larvae which in the period of investigation did not yet form schools, which perform the principal defensive function, were especially vulnerable for predators feeding on relatively large prey. The decrease of the part of small-sized prey at twilight is not related to their lesser availability due to a low illumination. It is assumed that feeding on energetically more valuable but less available prey is shifted to the period of low illumination when the larvae are less exposed to predation risk. The obtained results are discussed from positions of the triotroph concept (Manteifel’, 1961).     

Trafficking of the Phosphoprotein PfCRT to the Digestive Vacuolar Membrane in Plasmodium falciparum

The digestive vacuole plays an important role in the pathophysiology of the human malaria parasite Plasmodium falciparum. It is a terminal degradation organelle involved in the proteolysis of the host erythrocyte's haemoglobin; it is the site of action of several antimalarial drugs and its membrane harbours transporters implicated in drug resistance. How the digestive vacuole recruits residential proteins is largely unknown. Here, we have investigated the mechanism underpinning trafficking of the chloroquine resistance transporter, PfCRT, to the digestive vacuolar membrane. Nested deletion analysis and site‐directed mutagenesis identified threonine 416 as a functional residue for sorting PfCRT to its site of residence. Mass spectroscopy demonstrated that threonine 416 can be phosphorylated. Further phosphorylation was detected at serine 411. Our data establish PfCRT as a phosphoprotein and suggest that phosphorylation of threonine 416 is a possible deciding signal for the sorting of PfCRT to the digestive vacuolar membrane.     

The digestive systems of carnivorous plants

To survive in the nutrient-poor habitats, carnivorous plants capture small organisms comprising complex substances not suitable for immediate reuse. The traps of carnivorous plants, which are analogous to the digestive systems of animals, are equipped with mechanisms for the breakdown and absorption of nutrients. Such capabilities have been acquired convergently over the past tens of millions of years in multiple angiosperm lineages by modifying plant-specific organs including leaves. The epidermis of carnivorous trap leaves bears groups of specialized cells called glands, which acquire substances from their prey via digestion and absorption. The digestive glands of carnivorous plants secrete mucilage, pitcher fluids, acids, and proteins, including digestive enzymes. The same (or morphologically distinct) glands then absorb the released compounds via various membrane transport proteins or endocytosis. Thus, these glands function in a manner similar to animal cells that are physiologically important in the digestive system, such as the parietal cells of the stomach and intestinal epithelial cells. Yet, carnivorous plants are equipped with strategies that deal with or incorporate plant-specific features, such as cell walls, epidermal cuticles, and phytohormones. In this review, we provide a systematic perspective on the digestive and absorptive capacity of convergently evolved carnivorous plants, with an emphasis on the forms and functions of glands.

A comparison of the forms and functions of digestive and absorptive glands in carnivorous plants sheds light on their convergent evolution.     

Diet quality and food limitation affect the dynamics of body composition and digestive organs in a migratory songbird (Zonotrichia albicollis)

Migrating songbirds interrupt their feeding to fly between stopover sites that may vary appreciably in diet quality. We studied the effects of fasting and food restriction on body composition and digestive organs in a migratory songbird and how these effects interacted with diet quality to influence the rate of recovery of nutrient reserves. Food limitation caused white-throated sparrows to reduce both lean and fat reserves, with about 20% of the decline in lean mass represented by a decline in stomach, small intestine, and liver. During refeeding on diets similar in nutrient composition to either grain or fruit, food-limited grain-fed birds ate 40% more than did control birds, and they regained body mass, with on average 60% of the increase in body mass composed of lean mass including digestive organs. In contrast, food-limited fruit-fed birds did not eat more than did control birds and did not regain body mass, suggesting that a digestive constraint limited their food intake. The interacting effects of food limitation and diet quality on the dynamics of body composition and digestive organs in sparrows suggest that the adequacy of the diet at stopover sites can directly influence the rate of recovery of body reserves in migrating songbirds and hence the pace of their migration.