Invasive Activity of Allogromia Pseudopodial Networks: Skyllocytosis of a Gelatin/Agar Gel1

Time-lapse phase-contrast videomicroscopy revealed that the psudopodial network of two allogromiid foraminiferense display an invasive behaviour, previously undescribed, which I term Skyllocytosis (Greek: skylo—to rend, tear, pluck). When these networks encounter an interface between a gelatin/agar overlay and a glass substratum, portions of the overlay are penetrated and partly surrounded by reticulopodia. By the coordinated activity and contraction of these reticulopodia, small segments of the overlay are ripped away. Manageable portions of the overlay are subsequently transported towords the cell body. In carnivorous foraminifera skyllocytosis may account for the removal of soft, autolysed tissues from dead invertebrate prey.     

Prey capture and digestion in the carnivorous sponge<Emphasis Type="Italic"> Asbestopluma hypogea</Emphasis> (Porifera: Demospongiae)

Asbestopluma hypogea (Porifera) is a carnivorous species that belongs to the deep-sea taxon Cladorhizidae but lives in littoral caves and can be raised easily in an aquarium. It passively captures its prey by means of filaments covered with hook-like spicules. Various invertebrate species provided with setae or thin appendages are able to be captured, although minute crustaceans up to 8 mm long are the most suitable prey. Transmission electron microscopy observations have been made during the digestion process. The prey is engulfed in a few hours by the sponge cells, which migrate from the whole body towards the prey and concentrate around it. A primary extracellular digestion possibly involving the activity of sponge cells, autolysis of the prey and bacterial action results in the breaking down of the prey body. Fragments of the prey, including connective cells and muscles, are then phagocytosed and digested by archaeocytes and bacteriocytes. The whole process takes 8–10 days for a large prey. This unique feeding habit implies the capture and digestion of a macro-prey without any digestive cavity. It would appear to be an adaptation to life in deep-sea oligotrophic environments. Carnivorous sponges provide actual evidence, through a functional example, that a transition is possible from the filter-feeder poriferan body plan towards a different organizational plan through loss of the aquiferous system, a transition that has been hypothesized for the early evolution of Metazoa.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

How snakes eat snakes: the biomechanical challenges of ophiophagy for the California kingsnake, Lampropeltis getula californiae (Serpentes: Colubridae)

In this study we investigated how ophiophagous snakes are able to ingest prey snakes that equal or exceed their own length. We used X-ray video, standard video, dissection, and still X-rays to document the process of ophiophagy in kingsnakes (Lampropeltis getula) feeding on corn snakes (Elaphe guttata). Most kingsnakes readily accepted the prey snakes, subdued them by constriction, and swallowed them head first. In agreement with previous observations of ophiophagy, we found that the predator snake forces the vertebral column of the prey snake to bend into waves. These waves shorten the prey's body axis and allow it to fit inside the gastrointestinal (GI) tract and body cavity of the predator. Dissection of a kingsnake immediately following ingestion revealed extensive longitudinal stretching of the anterior portion of the GI tract (oesophagus and stomach), and no visible incursion of the prey into the intestine. X-ray video of ingestion showed that the primary mechanism of prey transport was the pterygoid walk, with some contribution from concertina-like compression and extension cycles of the predator's vertebral column in two out of three observations. Complete digestion was observed in only one individual, as others regurgitated before digestion was finished. X-ray stills taken every 4 days following ingestion revealed that the corn snakes were about half digested within the first 4 days, and digestion was complete within 15 days.     

The digestive process of the dinoflagellate, Oxyrrhis marina Dujardin, feeding on the chlorophyte, Dunaliella primolecta Butcher: a combined study of ultrastructure and free amino acids

The digestive process of Oxyrrhis marina Dujardin feeding on Dunaliella primolecta Butcher commences with the capture of the phototroph, perhaps involving trichocysts which restrain the prey, followed by engulfing by a membrane that appears to originate from near the fiagella pit of the O. marina. The prey, still within the capture membrane, enters the O. marina and is digested over a period estimated to be of the order of 12-24h. During digestion the prey first becomes more electron dense and the contents coagulate. Later the prey becomes less distinct and disintegrates; by this stage remains from several prey may be enclosed within one vacuole. Small O. marina , captured by large prey-depleted O. marina , suffer the same fate. Absence of any correlation between changes in intracellular amino acids and digestion of prey probably resulted from each O. marina containing several prey at various stages of digestion. However, the value of the glutamine/glutamate (Gln/Glu) ratio remained at around 0-3, whilst the population changed from one dominated by N-replete D. primolecta to one dominated by prey-replete O. marina , N-deplete D. primolecta and prey-deplete O. marina both have Gln/Glu of < 0.1. The Gln/Glu ratio may therefore be of use in assessing the nutrient status of heterotrophic microflagellates.     

Ultrastructure and histochemistry,of the stomach of Asplanchna sieboldi

Stomach cells of female Asplanchna sieboldi are specialized for absorption and intracellular digestion of nutrients. Evidence is presented to show that electron-opaque colloidal substances, present in the medium and within digestive vacuoles of the prey (Paramecium), are taken up by the stomach cells at the apical cell membrane and sequestered within food vacuoles which contain hydrolases working in both the acid and alkaline pH range. The stomach cells are also implicated in the absorption of molecules below the resolving power of the electron microscope. In rotifers possessing a complete digestive tract, this task is presumed to be handled by the intestine.     

A method for in situ estimation of prey selectivity and predation rate in large plankton, exemplified with the jellyfish Aurelia aurita (L.)

A method to estimate predation rates of large predatory zooplankton, such as jellyfish and ctenophores, is outlined. Large plankton size allows direct visual tracking of the predator during the process of foraging. The presented method is novel in the sense that it measures predation rate of a specific individual plankton predator in situ.After prey has been evacuated from the gut of an individual predator, the predator is incubated in situ, and observed by SCUBA-divers who recapture the individual after a defined time. Given that this incubation time is shorter than prey digestion time, predation rate can be calculated as increase in gut content over time. Clearance rates for different prey can be calculated from predation rates and prey concentrations in the water, allowing accurate estimates of prey selectivity. Thus, the problem of unknown feeding history and feeding environment, which can otherwise be a problem in prey selectivity studies of in situ-captured predators, is circumvented. Benefits and limitations of the method are discussed.The method was applied to adult medusae of the common jellyfish Aurelia aurita. A large variation in number of captured prey was detected both among individual jellyfish and among the various oral arms and gastric pouches within individuals. Clearance rates varied strongly with prey type. The medusae selected large crustacean prey (cladocerans and copepods/copepodites) over echinoderm larvae and copepod nauplii. Prey distribution within the medusae indicates that both tentacles and oral arms were used as prey capturing sites. Food passage time from prey capturing organs to gastric pouches was estimated.     

Feeding by larvae of Hypoatherina tropicalis (Pisces: Atherinidae) and its relation to prey availability in One Tree Lagoon,Great Barrier Reef,Australia

Synopsis Feeding of and food availability for larvae of Hypoatherina tropicalis were investigated in One Tree Lagoon, Great Barrier Reef, Australia, during November 1981 and January 1982. These surface-dwelling larvae and their microzooplankton prey were sampled as near to simultaneously as possible on 12 occasions during the daytime. Larvae of all sizes (5–17 mm SL) fed successfully over the observed range of mean prey densities (12–235 per liter), and the overall feeding incidence was 98.9%. Larger larvae consumed greater numbers and more categories of prey than did smaller larvae. Larvae selected copepods of all sizes, and nauplii, gastropods, bivalves, and foraminiferans that were greater than 75 ¢s mm in width. Tintinnids (mostly 37–74 µm in width) were generally avoided by larvae, but were occasionally important in the diets when they constituted more than 60% of the total available prey, regardless of the density of the selected prey categories. Larvae less than 14 mm SL ingested meroplankton (gastropods, bivalves, foraminiferans, and polychaetes) in direct relation to the densities available, and without regard to the densities of copepods available. However, the largest larvae (14–17 mm SL) ingested meroplankton in inverse relation to the density of copepods available, indicating that larvae consumed more meroplankton when the concentration of copepods was low. Such flexibility and opportunism in feeding behavior may increase the larvae's chances of obtaining adequate nutrition during periods of suboptimal feeding conditions.     

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%).     

Foraminiferan (Protozoa) epizoites on deep-water arcturids (Crustacea,Isopoda)

Foraminiferan (Protozoa) epizoites were examined on two deep-water isopods, Neastacilla sp. and Pleuroprion hystrix (Valvifera, Arcturidae), from the north Atlantic Ocean and the Nordic Seas. Most foraminiferans belonged to genus Cibicides and occurred on 27% of Neastacilla and 23% of Pleuroprion hystrix. The pattern of foraminiferan epibiosis was similar in both species, with a concentration on the dorsal body and on the posterior pereopods. The arcturids showed an increase in number of foraminiferans with increased body size, suggesting that available time span for settling on the younger stages (mancas) was relatively short. There was a trend towards larger numbers of foraminiferans occurring on larger arcturid species, suggesting that available space is the factor that determines the total number of foraminiferans for epibenthic arcturid isopod species.     

Selective association and transport of Campylobacter jejuni through M cells of rabbit Peyer's patches

M cells in the Peyer's patches may facilitate transport of pathogens such as Campylobacter jejuni from the intestine. We evaluated this hypothesis by using electron microscopy to examine Peyer's patches in ligated adult rabbit ileal loops inoculated with 5-mL suspensions of 10(9) cfu/mL of Campylobacter jejuni. Peyer's patches taken at intervals from 15 min to 2 h after inoculation of loops in anaesthetized rabbits provided evidence that Campylobacter jejuni selectively adhered to M cells as opposed to absorptive epithelial cells and was transported, apparently intact, into the M cell follicle. Although intercellular organisms were seen within the follicle, many others were phagocytosed by lymphoid cells. The proximity of the lymphatic and blood circulatory systems to the M cell follicle makes this a probable route for systemic spread of Campylobacter jejuni.     

Amplified detection, using a monoclonal antibody, of an aphid-specific epitope exposed during digestion in the gut of a predator.

Monoclonal antibodies are invaluable tools for identifying and quantifying prey remains in the fore-guts of predators. However, they must be target-specific, detect an epitope that is well replicated within the prey (to enhance assay sensitivity) and, critically, recognise a site that can resist digestion. A monoclonal antibody is reported that proved to be aphid-specific and capable of detecting, and accurately identifying, as little as 16.5 ng of aphid protein within a heterologous mixture of invertebrate material. The antibody was selected by screening hybridoma lines for antibodies that bound with semi-digested aphid proteins. The antibody detected an epitope that was found, against expectation, to significantly increase in concentration with time (by approx. 50% over 6 h) in the gut of the carabid predator Pterostichus melanarius. The resultant extended antigen detection period and half-life, and the high specificity of this antibody, showed it to be an enhanced tool for studying interactions between aphids and their predators in the field. It was concluded that the antibody was initially generated to a surface epitope on a high molecular weight native protein (> 200 kD). This epitope, however, was then either replicated on internal sites progressively revealed by digestion, or new epitopes became available as the conformation of the protein changed during digestion.     

The Oral Gland Cells of Oikopleura dioica (Tunicata Appendicularia)

Light and electron microscopic studies showed that the oral gland cells have two quite different zones. Medially, the basal zone is in contact with body fluids and the endostyle. Its strongly pyroninophile cytoplasm contains the extremely digitated nucleus and numerous small mitochondria. Laterally, the apical zone contacts the epidermis and it may also send a process between epidermal cells and deliver cell fragments into the primordium of the new house. This cell zone contains numerous membranes. It is concluded that the oral gland cells are light producing glands and that the membrane-rich cell fragments which are incorporated into the house wall are the source of the bioluminiscence which has been reported from empty houses. The ontogenetically related subchordal cells have a similar structure and it is possible that also these cells are light producers.     

Does Formation of Multicellular Colonies by Choanoflagellates Affect Their Susceptibility to Capture by Passive Protozoan Predators?

Microbial eukaryotes, critical links in aquatic food webs, are unicellular, but some, such as choanoflagellates, form multicellular colonies. Are there consequences to predator avoidance of being unicellular vs. forming larger colonies? Choanoflagellates share a common ancestor with animals and are used as model organisms to study the evolution of multicellularity. Escape in size from protozoan predators is suggested as a selective factor favoring evolution of multicellularity. Heterotrophic protozoans are categorized as suspension feeders, motile raptors, or passive predators that eat swimming prey which bump into them. We focused on passive predation and measured the mechanisms responsible for the susceptibility of unicellular vs. multicellular choanoflagellates, Salpingoeca helianthica, to capture by passive heliozoan predators, Actinosphaerium nucleofilum, which trap prey on axopodia radiating from the cell body. Microvideography showed that unicellular and colonial choanoflagellates entered the predator's capture zone at similar frequencies, but a greater proportion of colonies contacted axopodia. However, more colonies than single cells were lost during transport by axopodia to the cell body. Thus, feeding efficiency (proportion of prey entering the capture zone that were engulfed in phagosomes) was the same for unicellular and multicellular prey, suggesting that colony formation is not an effective defense against such passive predators.     

Morphology and function of the feeding apparatus of the lungfish, Lepidosiren paradoxa (Dipnoi)

The feeding mechanism of the South American lungfish, Lepidosiren paradoxa retains many primitive teleostome characteristics. In particular, the process of initial prey capture shares four salient functional features with other primitive vertebrates: 1) prey capture by suction feeding, 2) cranial elevation at the cranio-vertebral joint during the mouth opening phase of the strike, 3) the hyoid apparatus plays a major role in mediating expansion of the oral cavity and is one biomechanical pathway involved in depressing the mandible, and 4) peak hyoid excursion occurs after maximum gape is achieved. Lepidosiren also possesses four key morphological and functional specializations of the feeding mechanism: 1) tooth plates, 2) an enlarged cranial rib serving as a site for the origin of muscles depressing the hyoid apparatus, 3) a depressor mandibulae muscle, apparently not homologous to that of amphibians, and 4) a complex sequence of manipulation and chewing of prey in the oral cavity prior to swallowing. The depressor mandibulae is always active during mouth opening, in contrast to some previous suggestions. Chewing cycles include alternating adduction and transport phases. Between each adduction, food may be transported in or out of the buccal cavity to position it between the tooth plates. The depressor mandibulae muscle is active in a double-burst pattern during chewing, with the larger second burst serving to open the mouth during prey transport. Swallowing is characterized by prolonged activity in the hyoid constrictor musculature and the geniothoracicus. Lepidosiren uses hydraulic transport achieved by movements of the hyoid apparatus to position prey within the oral cavity. This function is analogous to that of the tongue in many tetrapods.     

Intracellular localisation of some peptidases and α-mannosidase in cotyledons of resting kidney bean, Phaseolus vulgaris

Cotyledons of resting kidney beans ( Phaseolus vulgaris , L., cv. "Processor") contain high activities of two alkaline peptidases, an aminopeptidase (EC 3.4.11) acting on Leu-Tyr and Leu-Gly-Gly and a dipeptidase (EC 3.4.13) hydrolysing Ala-Gly together with low activities of neutral naphthyiamidases (marker substrate Leu-β-NA) and of acid carboxypeptidases (EC 3.4.16; marker substrate Z-Phe-Ala). The intracellular localisation of these peptidases and that of α-mannosidase (EC 3.2.1.24) was studied by subcellular fractionations in different media. In density gradient centrifugations in non-aqueous glycerol-potassium iodide media the alkaline peptidases remained mainly in the application zone suggesting localisation in the cytosol. The carboxypeptidase and α-mannosidase activities banded mainly in the protein body zone, but about 15–30% of each activity was found in the cell wall zone. Results obtained by short centrifugation in glycerol or high-density sucrose solutions (65/70%) and by the isolation of essentially pure cell wall fractions confirmed these assignments. The results are in accordance with previous suggestions that the abundant alkaline peptidases may play a role in the mobilization of reserve proteins in germinated seeds by hydrolysing peptides which are produced initially within the protein bodies by acid proteinases and carboxypeptidases and which subsequently leak out or are transported from the autolyzing protein bodies to the cytosol.     

Developmental changes in the structure and function of mouthparts of phyllosoma larvae of the packhorse lobster, Jasus verreauxi (Decapoda: Palinuridae)

Mouthpart morphology and feeding behaviour of Jasus verreauxi phyllosomas (instars 1-13) were examined using scanning electron microscopy and video analysis, respectively, to better understand ingestion and processing mechanisms and to identify developmental changes in feeding biology. The density, robustness and complexity of mouthpart setation increased with development, oral field increased and there were a greater number of spinose projections on maxillae 1 in mid and late instar phyllosomas. The second and third maxillipeds were able to sweep a larger area due to their increased length, which effectively increased the size of the oral field. Changes in feeding behaviour were consistent with these morphological differences between instars. In late instars, the shredding and tearing efficiency of maxillae 1 increased, larger pieces of prey were pushed between the mandibles, and the mandibles were able to effectively grind food due to a slight rotation away from the transverse plane. Both morphological and behavioural observations suggests that the absolute size range of prey increases with phyllosoma body size and the prey processing (i.e. ability to capture, manipulate and grind prey) becomes more efficient with development. We suggest early instar phyllosoma are most suited to a diet comprising softer prey items, whereas later-instar phyllosoma are better equipped to deal with larger, fleshier prey.     

Nahrungsaufnahme und Verdauung bei der ForaminifereAllogromia laticollaris

Individual cells of the monothalamous foraminiferAllogromia laticollaris Arnold were fedSaccharomyces cerevisiae orSchizothrix calcicola after starvation periods of 14–24 hours. The fed cells were then examined electron-microscopically after different time intervals. Food organisms, “grasped” by the reticulopodia, are enclosed by a network of numerous cytoplasmic sub-strands and transported extracellularly into the shell-covered cell-body by means of cytoplasmic streaming of rhizopodia. The prey (yeast cells) is not completely surrounded by cytoplasm, i. e., a food vacuole is not formed. Inside the cell-body, yeast cells remain within the lacunary system; they are distributed throughout the cell. Special food vacuoles do not occur within the cell-body either; food particles are broken down within the lacunes of the vacuolar system. Thus, digestion takes place in an extracellular milieu. The numerous fine cytoplasmic strands, extending through the sea-water filled lacunes, must be regarded as of great importance for exchange processes, especially for the resorption of digested substrates. This extracellular digestion within the cell-body ofA. laticollaris parallels digestion in the digestive tract of higher animals. Indigestible food residues are removed by a reversal of the ingestion processes.     

Glial cells phagocytose neuronal debris during the metamorphosis of the central nervous system in Drosophila melanogaster

 Using electron microscopy we demonstrate that degenerating neurons and cellular debris resulting from neuronal reorganization are phagocytosed by glial cells in the brain and nerve cord of the fruitfly Drosophila melanogaster during the first few hours following pupariation. At this stage several classes of glial cells appear to be engaged in intense phagocytosis. In the cell body rind, neuronal cell bodies are engulfed and phagocytosed by the same glial cells that enwrap healthy neurons in this region. In the neuropil, cellular debris in tracts and synaptic centres resulting from metamorphic re-differentiation of larval neurons is phagocytosed by neuropil-associated glial cells. Phagocytic glial cells are hypertrophied, produce large amounts of lysosome-like bodies and contain a large number of mitochondria, condensed chromatin bodies, membranes and other remains from neuronal degeneration in phagosomes. Received: 23 January 1996 / Accepted in revised form: 21 May 1996     

Ontogenetic changes in habitat use by whitefish,Coregonus lavaretus

Synopsis The whitefish, Coregonus lavaretus, in the lake Mj?sa exhibited two niche changes during their life cycle. Juveniles (< 25 cm body length) were confined to the shallow (0–30 m) epibenthic zone. Medium sized whitefish (25–35 cm body length) expanded their habitat use to include the deep (30–90 m) epibenthic zone as well as the pelagic zone. From a body length of 35 cm, habitat use was restricted to the deep epibenthic zone. Small fish in the shallow epibenthic zone ate small and medium-sized prey (zooplankton, insect larvae and surface insects). Medium-sized fish in this zone were in addition feeding on the larger amphipod, Pallasea quadrispinosa. In the pelagic zone, the diet of medium-sized whitefish was dominated by zooplankton, although some larger prey like surface insects and age-0 smelt, Osmerus eperlanus, were also eaten. In the deep epibenthic zone, the diet of both medium-sized and large (< 35 cm) whitefish consisted mainly of the large prey P. quadrispinosa.     

Phagocytosis of collagen fibrils by periosteal fibroblasts in long bone explants. Effect of concanavalin A

In an attempt to determine whether phagocytosis of collagen by fibroblasts involves binding of the fibril to the plasma membrane, the effect of the lectin concanavalin A (Con A) was studied in an in vitro model system. Metacarpal bone rudiments from 19-day-old mouse fetuses were incubated with varying concentrations of the lectin. Quantitative electron microscopic analysis indicated that Con A caused a dose-related increase in the amount of phagocytosed collagen fibrils in periosteal fibroblasts, suggesting either an enhanced uptake or a decreased intracellular breakdown of fibrils. Since a Con A-inducible increase was not seen in the combined presence of both the lectin and the proteinase inhibitor leupeptin, which is known to inhibit the intracellular digestion of phagocytosed fibrillar collagen, it is unlikely that Con A stimulated phagocytosis. Based on the finding that Con A interfered with the digestion of a synthetic substrate by the collagenolytic lysosomal enzyme cathepsin B it is suggested that the augmentation of intracellular fibrillar collagen under the influence of the lectin was due to a decreased intracellular digestion. Since Con A did not inhibit the uptake of collagen fibrils by the fibroblasts it is concluded that Con A-inhibitable binding sites for collagen molecules are unlikely to be involved in phagocytosis of collagen fibrils by fibroblasts.