Utilization of exogenous glucose by the rediae of Parorchis acanthus (Digenea: philophthalmidae) and Cryptocotyle lingua (Digenea: heterophyidae)

Parasitism enhances gastropod feeding on invasive and native algae while altering essential energy reserves for organismal homeostasis upon warming

Marine bioinvasions are of increasing attention due to their potential of causing ecological and economic loss. The seaweed Gracilaria vermiculophylla has recently invaded the Baltic Sea, where, under certain conditions, it was found to outcompete the native alga Fucus vesiculosus. Parasites of grazers and temperature are among the potential factors which might indirectly modulate the interactions between these co-occurring algae through their single and combined effects on grazing rates. We tested the temperature and parasitism effects on the feeding of the gastropod Littorina littorea on F. vesiculosus vs. G. vermiculophylla. Uninfected and trematode-infected gastropods were exposed to 10, 16, 22, and 28 °C for 4 days while fed with either algae. Faeces production was determined as a proxy for grazing rate, and HSP70 expression, glycogen and lipid concentrations were used to assess the gastropod's biochemical condition. Gracilaria vermiculophylla was grazed more than F. vesiculosus. Trematode infection significantly enhanced faeces production, decreased glycogen concentrations, and increased lipid concentrations in the gastropod. Warming significantly affected glycogen and lipid concentrations, with glycogen peaking at 16 °C and lipids at 22 °C. Although not significant, warming and trematode infection increased HSP70 levels. Increased faeces production in infected snails and higher faeces production by L. littorea fed with G. vermiculophylla compared to those which fed on F. vesiculosus, suggest parasitism as an important indirect modulator of the interaction between these algae. The changes in the gastropod's biochemical condition indicate that thermal stress induced the mobilization of energy reserves, suggesting a possible onset of compensatory metabolism. Finally, glycogen decrease in infected snails compared to uninfected ones might make them more susceptible to thermal stress.

Parasitic infection alters the physiological response of a marine gastropod to ocean acidification

Increased hydrogen ion concentration and decreased carbonate ion concentration in seawater are the most physiologically relevant consequences of ocean acidification (OA). Changes to either chemical species may increase the metabolic cost of physiological processes in marine organisms, and reduce the energy available for growth, reproduction and survival. Parasitic infection also increases the energetic demands experienced by marine organisms, and may reduce host tolerance to stressors associated with OA. This study assessed the combined metabolic effects of parasitic infection and OA on an intertidal gastropod,Zeacumantus subcarinatus. Oxygen consumption rates and tissue glucose content were recorded in snails infected with one of three trematode parasites, and an uninfected control group, maintained in acidified (7·6 and 7·4 pH) or unmodified (8·1 pH) seawater. Exposure to acidified seawater significantly altered the oxygen consumption rates and tissue glucose content of infected and uninfected snails, and there were clear differences in the magnitude of these changes between snails infected with different species of trematode. These results indicate that the combined effects of OA and parasitic infection significantly alter the energy requirements ofZ. subcarinatus, and that the species of the infecting parasite may play an important role in determining the tolerance of marine gastropods to OA.

Variations in the Metabolism of the Daughter Sporocysts of Microphallus pygmaeus in a Chemically Defined Medium

A comparison is made of the variations in the mean size (length), reduced weight, oxygen uptake, metabolic rate and the number of contained fully formed metacercariae undergoing autolysis, in mature daughter sporocysts of Microphallus pygmaeus, in sea water, artificial sea water and in a chemically defined nutrient medium (modified medium 199). The work indicates that the sporocysts begin to degenerate almost immediately in the non-nutrient media but have a higher metabolic activity and remain healthy for up to 36 days in the nutrient medium.

The ultrastructure of the fore-gut of the redia of Parorchis acanthus Nicoll (Digenea: Philophthalmidae) from the digestive gland of Nucella lapillus L

The fore-gut of the redia of Parorchis acanthus is ingestive in function. It consists of a buccal cavity, suctorial pharynx and an oesophagus divided into anterior and posterior regions. The syncytial lining is continuous with that covering the body surface, except for the posterior region of the oesophagus which is lined by a separate syncytium. This latter has different cytoplasmic inclusions and the unusual feature of a single ventral nucleus in the outer cytoplasmic epidermis. Intrinsic and extrinsic muscles are responsible, respectively, for the fairly rapid passage of food through the fore-gut and for support. Secretion bodies in the epidermis are probably discharged into the lumen and pass with food into the intestine where they may be involved in extracellular digestion. Young rediae feed mainly by mouth while older, immotile rediae absorb nutrients mainly through the body surface.

The ultrastructure of the intestine of the redia of Parorchis acanthus Nicoll (Digenea: Philophthalmidae) from the digestive gland of Nucella lapillus L

The intestine of the redia of Parorchis acanthus is lined by a gastrodermis and surrounded by inner longitudinal and outer circular muscles. The gastrodermis consists of alternating rings of dense and lucent cells of similar dimensions, with similar nuclei and with microvilli on the lumenal surface. The dense cells contain ribosomes, dense secretion bodies, vesicles and a few lipid bodies. Ribosomes, dense bodies and lipids are absent from the lucent cells but vesicles are present which, as in the dense cells, pass along the microvilli to be discharged into the lumen. Both types of cells are secretory, absorptive and transportive. The lucent cells, in addition, store glycogen in areas of the cytoplasm devoid of organelles. Tips of processes from the parenchyma cells are engulfed in pockets in the basal plasma membrane, of both, facilitating transport of nutrients from the gastrodermis directly into the parenchyma

Parasites alter community structure

Parasites often play an important role in modifying the physiology and behavior of their hosts and may, consequently, mediate the influence hosts have on other components of an ecological community. Along the northern Atlantic coast of North America, the dominant herbivorous snail Littorina littorea structures rocky intertidal communities through strong grazing pressure and is frequently parasitized by the digenean trematode Cryptocotyle lingua. We hypothesized that the effects of parasitism on host physiology would induce behavioral changes in L. littorea, which in turn would modulate L. littorea's influence on intertidal community composition. Specifically, we hypothesized that C. lingua infection would alter the grazing rate of L. littorea and, consequently, macroalgal communities would develop differently in the presence of infected versus uninfected snails. Our results show that uninfected snails consumed 40% more ephemeral macroalgal biomass than infected snails in the laboratory, probably because the digestive system of infected snails is compromised by C. lingua infection. In the field, this weaker grazing by infected snails resulted in significantly greater expansion of ephemeral macroalgal cover relative to grazing by uninfected snails. By decreasing the per-capita grazing rate of the dominant herbivore, C. lingua indirectly affects the composition of the macroalgal community and may in turn affect other species that depend on macroalgae for resources or habitat structure. In light of the abundance of parasites across systems, we suggest that, through trait-mediated indirect effects, parasites may be a common determinant of structure in ecological communities.

Incorporation of exogenous D-glucose-1-(14)C and D-manose-1-(14)C into glycogen and lactate excreted by Angiostrongylus cantonensis in vitro

The amount of labelled glucose incorporated into glycogen is 6 times as much as that of labelled mannose by the female worms. They excreted lactate of labelled glucose-origin 3-4 times as much as that of labelled mannose-origin. The amount of labelled glucose incorprated in worm bodies is about 3 times as much as that of labelled mannose. Male worms absorbed a half amount of glucose by female worms. Paralelled with radioactivity studies mentioned above, chemical determinations of sugars, lactate, and glycogen were performed on the media prior and posterior to incubation and the worms. The results obtained from chemical determinations fairly agreed with those on lactate production and sugar consumption from radioactivity studies, but not on glycogen content of worms after incubation. Chemical determination shows no glycogen synthesis in worms incubated in mannose media while the radioactivity of labelled mannose was detected, though it is very low in activity, from glycogen of worms in the media. Coupled with previously reported findings, results from the present study show mannose to be far less significant in the carbohydrate metabolism of Angiostrongylus cantonensis as compared with glucose.

Autoradiographic studies on the uprake of (14C)-glucose by Bithynia tentaculata (mollusca : Gastropoda) and its larval digeneans

Autoradiographs revealed that sporocysts of Cercaria helvetica XII and rediae of Sphaeridiotrema globulus, incubated in a medium containing [14C]-glucose, exhibited slight radioactivity in their body wall after only 30 seconds incubation. Activity in sporocysts and rcdiae gradually increased as the incubation period was extended until after 4 minutes, a heavy reaction was observed in the parasite body wall as well as in the germ balls and developing cercariae within the parasite brood chambers. The redial caecum appeared to incorporate the labelled compound much more intensely than did the redial body wall.

When uninfected Bithynia tentaculata, as well as B. tentaculata infected with either S. globulus or C. helvetica XII, were maintained in pond water containing [14C]-glucose, activity could be detected in the gills of both infected and uninfected snails after 5 hours incubation. After 12 hours a much heavier labelling was apparent in the gills, together with moderate activity in the haemocoelic spaces, foot musculature, stomach wall, and gut contents. After 20 hours a more intense labelling was apparent in these regions of the snail body and, in addition, some activity could be detected in the digestive gjand tubules of the host and, in infected snails, in the bodies of developing parasites. After 30 hours incubation the labelled compound had become incorporated into most of the host tissues but was most intense in the digestive gland tubules. Heavy activity was also evident in the parasites at this stage although certain cystogenous gland cells of the cercariae of both parasite species did not incorporate the labelled compound.

Amino acid flux in the sporocysts of Cercaria emasculans Pelseneer, 1906 in vitro

Quantitative paper chromatography and radioactive tracers were used to study the flux of alanine through the sporocysts ofCercaria emasculans in vitro. The following evidence indicates that simple diffusion is the main mechanism of permeation: (1) the sporocysts cannot accumulate alanine against a concentration gradient; (2) the concentration of alanine in the sporocysts is a direct linear function of the concentration of alanine in the external environment; (3) addition of 10−2M glucose to the medium does not enhance permeation; (4) neither heat-killing the sporocysts nor treating them with 10−3M iodoacetate slows the rate of permeation; (5) theQ10's for the permeation are similar to those to be expected in a process involving simple diffusion; (6) the amino acid molarities in the parasite and host tissuesin vivoare strikingly similar. No utilization of alanine during the course of 3 h incubations could be detected by autoradiography.

The dynamic nature of the equilibrium between the sporocysts and the external environment is emphasized by the exchange of alanine that occurred even under isotonic conditions.

Fresh sporocysts leaked alanine and proline during 1 and 4 h incubationsin vitro. The significance of this is not known.

Observations on the effect of the rediae of Fasciola hepatica on the lipid composition of the hepatopancreas of Lymnaea truncatula

In the uninfected hepatopancreas of L. truncatula 7·0–11·0% of the dry weight is lipid. Of the total lipid 60% is neutral lipid and 40% is phospholipid. Free fatty acid is the major neutral lipid component; triglycerides, diglycerides, monoglycerides, sterols and esterified sterols are also present. The phospholipids identified were phosphatidyl choline, phosphatidyl ethanolamine, lyso-phosphatidyl choline and sphingomyelin. The fatty acids were analysed by gas chromatography. The major fatty acid is C16 (palmitic) and 60% of the total fatty acids are saturated.

In the hepatopancreas of L. truncatula infected with the rediae of F. hepatica, but with the rediae removed, 5·4–9·4% of the dry weight is lipid. Of this total lipid 73% is neutral lipid and 27% is phospholipid. All the fractions of neutral lipid, except the fatty acids are smaller than in the uninfected hepatopancreas. The fatty acids show an increase of 38%. The same phospholipids identified in the uninfected hepatopancreas are present, but all the fractions show a decrease in amount with the exception of the phosphatidyl choline fraction, which is present in approximately equal amounts in both the uninfected and the infected hepatopancreas. The major fatty acid is palmitic acid.