Rearing density and susceptibility of Rana pipiens metamorphs to cercariae of a digenetic trematode

Cercariae of many digenean trematodes target particular developmental stages of their hosts. For some digeneans that are parasites of amphibians, infection appears timed to host metamorphosis. The success and timing of metamorphosis is itself affected by a number of factors, including host density. We investigated the degree to which rearing density of Rana pipiens larvae influenced time to metamorphosis and snout-to-vent length and mass at metamorphosis, as well as establishment of cercariae of the trematode Manodistomum syntomentera Stafford, 1905. As expected, individuals metamorphosed later, were smaller, and weighed less at metamorphosis if they were reared under intermediate to high densities compared with low densities, in experimental outdoor mesocosms. Cercariae establishment was higher in smaller metamorphs that took longer to metamorphose within the low-density treatment. Additionally, cercariae establishment was lower in larvae from the low-density tanks compared with larvae from the intermediate- to high-density tanks. However, more tadpoles had failed to metamorphose in the intermediate to high rearing densities by the time cercariae were no longer available from natural collections of first intermediate hosts, Physa spp. Larval amphibians under crowded conditions should experience increased susceptibility to trematode establishment in nature, but only if they metamorphose within the time period when cercariae are still available.     

Biochemical and histochemical studies of alkaline and acid phosphatases in a digenetic trematode, Pegosomum egretti

The biochemistry and histochemistry of Pegosomum egretti have been studied using standard techniques. Phosphatases were analysed colorimetrically; the optimum pH for acid phosphatase activity was 5.0 and for alkaline phosphatase was 10.0. The results were compared with those of other trematodes. Histochemical localization of acid and alkaline phosphatases revealed differences in enzymes activity in various tissues. These differences in the site and pattern of distribution of the two enzymes have been discussed in relation to transport of raw materials and the metabolism of the cell concerned.     

Alterations in Biomphalaria glabrata plasma induced by infection with the digenetic trematode Echinostoma paraensei

Alterations in the noncellular hemolymph components of M line Biomphalaria glabrata snails infected with the trematode Echinostoma paraensei for 1, 2, 4, 8, 15, 30, or 60 days were monitored by direct microscopical examination, and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in conjunction with quantitative densitometry. A prominent particulate substance was first noted in the hemolymph of infected snails at 1 day postexposure (PE), persisted through day 15, and subsided by day 30. This substance, which was not observed in control snails, contained 2 major polypeptides of 190-200 and 80-120 kDa. Infection with E. paraensei also induced substantial changes in soluble hemolymph polypeptides. PAGE lanes loaded with plasma samples from M line snails infected for 4, 8, 15, and 30 days exhibited a generalized increase in staining intensity relative to controls. A diffuse band centered at approximately 100 kDa, but of variable width, was selectively enriched relative to control preparations in snails with 4-, 8-, 15-, and 30-day-old infections. Standard protein assays also indicated an increase in total protein content of plasma samples from snails infected for 2-60 days, with significant increases noted at 4, 8, and 30 days. Infected snails of the 10-R2 strain of B. glabrata also contained particulate material in their hemolymph. However, soluble hemolymph components of 10-R2 snails exhibited relatively little change, or declined, as a result of infection. For either strain, no new bands could be detected in plasma samples from infected snails, nor were any bands consistently deleted as a result of infection. Although both snail strains exhibit alterations in hemolymph components as a result of infection, their responses differ qualitatively and quantitatively.     

Parasitic castration of Eurhomalea lenticularis (Bivalvia: Veneridae) by a digenetic trematode: quantitative histological analysis

The clam Eurhomalea lenticularis may be parasitized by digenean trematodes of the family Plagiorchidae, specifically in the gonads (parasitic castration). A quantitative histological analysis of the parasitized gonads demonstrated a significant decrease in gonadal area, in the size of individual acini, and in the numbers of differentiated germ cells compared to unparasitized clams. Castration may be caused by mechanical compression due to trematode sporocyst growth. However, the uniform loss of germ cells in areas without sporocysts suggests that a more generalized mechanism is responsible. We suggest that parasitic castration has a primary effect on the host's neuroendocrine and gametogenic systems that regulate gamete production.     

Factors influencing the distribution of digenetic trematode infections in a mudsnail (Hydrobia ventrosa) population inhabiting salt marsh ponds in Iceland

This study analyzed the influence of several abiotic and biotic variables on the distribution of digenetic trematode infections in a mudsnail, Hydrobia ventrosa, population inhabiting 12 ponds on the Melabakkar salt marsh in Iceland, the northwestern limits of the geographical distribution. Nine trematode species were found to infect the snail population, which included Microphallus pirum, Microphallus breviatus, Microphallus claviformis, Maritrema subdolum (Microphallidae), Cercaria Notocotylidae sp. 11 Deblock, 1980, C. Notocotylidae sp. 12 Deblock, 1980, C. Notocotylidae sp. 13 Deblock, 1980 (Notocotylidae), Cryptocotyle concavum (Heterophyidae), and Psilostomum brevicolle (Psilostomatidae). Correlations between biotic variables (snail density in the ponds and vegetation cover), abiotic variables (distance of each pond from the sea, pond elevation above chart datum, size, average depth, salinity, and some characters of the littoral zone and sediments), and trematode infections were analyzed. These variables indirectly affected the trematode infections because some determined how attractive the ponds were for the final hosts, which were various species of marine and shore birds. We propose that their habitat use and defecating habits are the main determinants of the trematode distribution in the area.     

Differences in shell shape of naturally infected Lymnaea stagnalis (L.) individuals as the effect of the activity of digenetic trematode larvae

The shells of Lymnaea stagnalis show great morphological variability. This phenomenon has been described as the result of an environmental influence. The main object of the present study was to compare some biometric data from shells of naturally infected and uninfected snails from 25 different lakes in the central part of Poland. The height of the shell, the height of the spiral, and the width of the shell were measured. Some inter- and intrapopulation differences among individuals were found. Greater variability of shell shape was observed among snails parasitized with digenean larvae than in nonparasitized ones. Snails infected with Echinoparyphium aconiatum, Echinostoma revolutum, Diplostomum pseudospathaceum, and Opisthioglyphe ranae differed in shell shape compared with uninfected individuals. Snails infected with Plagiorchis elegans did not differ from uninfected individuals. The same was true of snails in which the commensal oligochaete, Chaetogaster limnei, was found. The results of the present study support the assumption that the deformation of shells of the snails under study was in some way influenced by the presence of certain species of digenetic trematodes.     

Studies of pathogenicity of the digenetic trematode Ganeo tigrinum (Mehra et Negi) for the stomach of Rana tigrina (Daudin)

Ganeo tigrinum (Mehra et Negi) was seen to be attached to the stomach wall of Rana tigrina (Daudin) by suckers drawing out mucosal plugs. The tissues lodged inside the suckers were desquamated, ulcerated and necrosed. Encapsulated flukes were seen in the submucosa. The stomach wall was completely dissolved at the site of entry of the fluke, while adjacent tissues were compressed. The gastric mucosa was mechanically compressed by the fluke. Oedema, cellular infiltrate, dilated blood vessels and congested blood capillaries were seen in the infected stomach. PAS positive and alcian blue negative mucoid substances were present in large amounts in the lumen and in small amounts in the mucosal epithelial cells of the fluke-infected stomach.     

Enzyme activity in livers from chickens (Gallus domesticus) experimentally infected with the digenetic trematode, Amphimerus elongatus (Trematoda: Opisthorchiidae)

Day old Leghorn chickens were infected with the digenetic trematode Amphimerus elongatus. After different periods of growth, birds were sacrificed and liver enzyme activity determined for six enzymes. Specific activities of adenylate kinase, lactate dehydrogenase, malate dehydrogenase and phosphoglucomutase were significantly lower in infected chickens than in controls. Creatine kinase and glucosephosphate isomerase activities were unaffected by the parasite.     

Vicious circle in the intertidal: Facilitation between barnacle epibionts, a shell boring polychaete and trematode parasites in the periwinkle Littorina littorea

We studied interactions between three organisms associated with a common gastropod of northern Atlantic shores, the periwinkle Littorina littorea: barnacle epibionts Balanus crenatus, a shell boring polychaete Polydora ciliata, and tissue invading trematodes which use the periwinkles as first intermediate host. Snails collected shortly after barnacle settlement with > 50% cover of barnacles had significantly higher infestation of shell boring worms compared to unfouled snails, while trematode infestation was similar. The result was the same at two sites, and we conclude that the worm P. ciliata facilitates barnacle fouling on snails. The reverse was also the case. In an experiment with 14 weeks of exposure, snail treatments with barnacle epibionts had a significantly higher P. ciliata load than unfouled and cleaned snails. Again, trematode infestations were similar. The reciprocal positive interactions between barnacle epibionts and shell boring worms on snail houses is regarded as a case of facultative mutualism. On the other hand, for the snail basibiont, both barnacles and shell boring worms exert strongly negative effects by reducing fecundity, growth, and survival, resulting in a vicious circle for the snails. The combined effects of these associated organisms may rival in importance any competitive or predacious effects on the host L. littorea.     

Calcite in the mandibles of a marine polychaete

Calcite forms a thick pad on the anterior-ventral surface of the mandibles of Eunice aphroditois (Pallas) (Annelida, Polychaeta, Eunicida, Eunicea). The calcite pads apparently serve as an abrasive in feeding; they are possibly renewed by continuous calcite deposition. Mandibular calcite pads are not usually recognized in the fossil record because they are destroyed during the leaching of limestones for the recovery of scolecodonts.