Digestive Tract Of Larvae Research Articles

Responses of echinoid larvae to food patches of different algal densities

High densities of larvae have been found in areas of high primary production, but it remains unclear whether this is the result of hydrodynamics or of larval aggregative behaviour in the presence of food. In this study, we examined changes in the vertical distribution and swimming patterns of four-armed larvae of the sea-urchin Echinometra lucunter (Linnaeus) around food patches of a range of microalgal densities. We reared larvae in the laboratory in a high or low concentration of either single (Isochrysis galbana) or mixed (I. galbana, Dunaliella tertiolecta, Thalassiosira weissflogii) microalgal species. In Plexiglas cylinders, we experimentally constructed haloclines in which the salinity of the bottom water-layer was 33‰ and that of the top water-layer was 24‰. In a thin layer in the middle of the halocline, we inserted a food patch that consisted of 0, 2500, 5000 or 10 000 T. weissflogii cells ml−1. The presence of a food patch had a pronounced effect on the vertical distribution of larvae. This effect depended upon the algal density of the food patch and varied with dietary conditioning. The number of larvae that were above or within the patch decreased with increasing algal density, and was greater if larvae were reared in low-ration or single-species diets than in high-ration or mixed-species diets. Tracking of individual vertical swimming paths showed that within a few minutes, larvae swam into the patches of low algal density, and to positions just below the patches of the two higher algal densities, and remained there until the end of the experimental period. The greater number of algal cells in the digestive tracts of larvae from treatments with a food patch than in those without a patch confirmed that larvae were feeding on the microalgal cells of the patch. To our knowledge, this is the first study to experimentally show an aggregative behavioural response of invertebrate larvae to a food patch. Such a response may reduce the probability of food limitation and therefore enhance larval survival.

Expression of metallothionein genes during the post-embryonic development of Drosophila melanogaster.

Expression of the two Drosophila melanogaster metallothionein genes, Mtn and Mto, has been analyzed by in situ hybridization during post-embryonic development. Mtn and Mto transcripts were detected exclusively in the digestive tract of larvae, pupae and adults reared on standard medium. Mtn and Mto expression domains overlap, but each gene is also expressed at unique sites. Mtn mRNA levels are approximately 10 and 20 times higher than those of Mto in larvae and adults, respectively. Copper and cadmium ions strongly induce Mtn and Mto mRNA accumulation in the midgut. Zinc is a weaker inducer, acting only at high concentrations. Mtn gene expression is induced by these three metals in Malpighian tubules, while Mto gene expression in this organ is induced only by zinc. Iron is a poor inducer of metallothionein mRNA accumulation. Functions of MTN and MTO proteins in metal homeostasis and detoxification are considered.

A Comprehensive Program for the Evaluation of Artificial Diets

AbstractThe evaluation of artificial diets for marine fish larvae involves much more than feeding trials. Information on the diet in the water column (buoyancy, leaching, etc.), the digestive capabilities and requirements of the larvae, and the fate and uptake of the diet inside the larval digestive tract are all necessary to the understanding of the success or failure of a given artificial diet. Interdisciplinary teams of investigators are required to fully evaluate and formulate artificial diets.

Partial characterization of digestive tract proteinases from western corn rootworm larvae, Diabrotica virgifera

AbstractWe have partially characterized the proteolytic activity within luminal contents of the digestive tracts of larvae of the western corn rootworm, Diabrotic virgifera LeConte. At least 15 proteinases were detected based on chromatographic behavior on ion exchange high‐performance liquid chromatography and their mobility on sodium dodecyl sulfate gels containing gelatin. Inhibitors of proteolytic activity indicated that these enzymes are primarily sulfhydryl proteinases. Native polycrylamide gel electrophoresis revealed that a single proteinaceous inhibitor, egg white cystatin, was capable of abolishing a substantial part of the proteolytic acitivity. Our data suggest, accordingly, that gene transfer experiments utilizing the cystatin gene may generate lines of maize which have increased resistance to western corn rootworm larvae. © 1992 Wiley‐Liss, Inc.

A study on the bacterial flora of giant prawn, Macrobrachium rosenbergii, larvae fed with Artemia salina nauplii

A study was carried out to determine whether low survival rate during the early stages of Macrobrachium rosenbergii development correlated with bacteria associated with the prawns' first feed, nauplii of the brine shrimp Artemia salina. These bacteria and the bacterial flora present in the digestive tract of 1–30-day-old prawn larvae were analyzed and compared. Aeromonas liquefaciens and Vibrio anguillarum were the most common bacteria isolated from the prawn larva intestine but were absent from brine shrimp nauplii. A total of nine strains of bacteria isolated from both species were selected for experiments aimed at determining their pathogenicity. Larvae of three different ages were challenged with massive concentrations of each bacterial monoculture, but neither rapid mortalities ensued nor were any significant changes apparent in the intestinal floral composition. These results indicate the early establishment of an autochthonous, homeostatic bacterial flora in the larval digestive tract. In addition, the protozoans Epistylis and Zoothamnium and the fungus Lagenidium were detected. All of these were effectively controlled in vitro by 20 ppm of merthiolate. The role of these microorganisms as potential pathogens of prawn larvae is briefly discussed.

The role of the basal lamina in mouth formation in the embryo of the starfish Pisaster ochraceus.

Details of mouth formation in normal and exogastrulated Pisaster ochraceus larvae have been studied by light microscopy and transmission and scanning electron microscopy. As the archenteron begins to bend, the cells in the presumptive mouth region dissociate and migrate into the blastocoele where they become mesenchyme cells. This leaves a defect in the "blind" endodermal tube, which is covered by a basal lamina. Subsequently this exposed basal lamina bulges to form a blister which appears to extend across the blastocoele to make contact with spikelike projections from the future stomodeal region of the ectoderm. Mesenchyme cell processes are associated with both the basal lamina blister and the ectoderm in this region and may provide both motive power and guidance for contact. Shortly after contact is made the blister of basal lamina from the endoderm fuses with the basal lamina of the ectodermal cells and the ectoderm begins to invaginate. At this time the lateral walls of the presumptive oesophagus are largely formed of naked basal lamina with some loosely associated cells on the endodermal side. Eventually the lateral walls of the proximal part of the oesophagus become cellular, giving rise to an epithelium. A cell plug located between the stomodeum and oesophagus persists for some time before finally breaking down to complete the larval digestive tract. Experiments with exogastrulae suggest that many of these developmental patterns are determined before gastrulation.

Etude histoenzymologique des activites proteasiques dans le tube digestif des larves et des adultes de Bar, Dicentrarchus labrax (L)

A comparative study of pepsine-like (pH 2) and trypsin- or chymotrypsin-like (pH 9) activities in the digestive tract of larvae and adults of sea bass, Dicentrarchus labrax (L.) has been carried out using the substrate-film method. The results obtained suggest that, at the beginning of the exotroph phasis, the digestion of proteins is observed almost exclusively in the middle and posterior parts of the intestine. Gastric digestion with the participation of the secretions of the gastric glands occurs rather late in the early life. A proteolytic activity at pH 9 was revealed in the pyloric caeca. It is less marked in 8–10- month-old juveniles than in 45–60-day-old larvae.

Resolution of Proteases in the Keratinolytic Larvae of the Webbing Clothes Moth

The proteases of the larvae of the webbing clothes moth, Tineola bisselliella, were investigated because of this organism's phylogenetic rank as a member of the lower invertebrates, its unique position as one of the relatively few organisms that can digest keratin and its importance as a serious fabric pest. Both the number and nature of different proteolytic enzymes present were investigated and the various activities partially fractionated by ammonium sulphate precipitation and chromatography on DEAE-cellulose and Sephadex G200 columns. A complex mixture of peptidases and proteinases has been found in extracts of whole larvae and has been shown to be associated with the larval digestive tract. The proteinases include metal-chelator-sensitive proteinases (metalloproteinases) and serine proteinases but no SH-proteinases or acid proteinases. The serine proteinases include both trypsin-like and chymotrypsin-like activities. Four major and three minor anionic trypsin-like enzymes and a single major cationic trypsin-like enzyme have been detected. Only a single anionic chymotrypsin-like enzyme appears to be present. The trypsin-like enzymes are unaffected by the naturally occurring proteinase inhibitors, chicken ovomucoid, soybean trypsin inhibitor and lima bean trypsin inhibitor, while the chymotrypsin-like enzyme is inhibited by soybean trypsin inhibitor only. The enzymes resemble the serine proteinases from microorganisms in their pH stability. The peptidases include both aminopeptidase and carboxypeptidase activities and both are present in multiple forms. Sixteen aminopeptidase bands have been detected and all are present in individual larvae. They are not inhibited completely by reagents specific for any of the common active sites, and have different specificity requirements. Two carboxypeptidases have been detected on acrylamide gels and have been completely separated on DEAE-cellulose. No evidence could be found for the existence of any of these proteases as inactive precursors.

Bacteria in the Digestive Tract of Alfalfa Weevil Larvae1

A knowledge of the normal bacterial flora of an insect's digestive tract is important in identifying potential pathogens from diseased specimens. In a survey of the bacterial flora of various insect orders, Steinhaus (1941) isolated 83 different types of bacteria of which 53% were gram negative rods. In the Coleoptera 86% of the 21 types isolated were gram negative rods. Other workers (Buchner and Stephens 1959, Stevenson 1966) investigating species of Orthoptera found a more heterogenous composition of bacteria. The present paper reports on the isolation and identification of bacteria from the digestive tract of larvae of the alfalfa weevil, Hypera postica (Gyllenhal).

A Qualitative Analysis Of The Digestive Secretions Of The Larva Of The Japanese Beetle (Popillia Japonica Newm.)1

An analysis of the secretions of the digestive tract of larvae has shown the presence of the basic ions of aluminum, ferrous iron, calcium, magnesium, potassium, sodium, and ammonium. The acidic ions found present were carbonate, chloride, nitrite, and phosphate.