Effects of trematode double infection on the shell size and distribution of snail hosts

Infection with larval trematodes sometimes alters the phenotypes of their snail hosts. While some trematode species have distinct effects on host phenotypes, it is still unclear how snail phenotypes are altered when they are parasitized with multiple trematode species. Here, we report that double infection with trematode species averages the effects of parasitic alteration on host phenotype. We found that snail hosts Batillaria attramentaria (Batillariidae) infected with Cercaria batillariae (Heterophyidae) have abnormally large shells and distribute in lower areas of the intertidal zone. Snails with another dominant trematode species, the renicolid cercaria I (Renicolidae), have slightly larger shells and distribute in upper areas of the intertidal zone. A number of double infections with both trematodes was observed in this study. Snails infected with both trematode species exhibited an intermediate size and inhabited a depth between those of snails solely infected with either trematode species, suggesting that the two trematodes simultaneously affected the snail phenotypes. Because altered host phenotypes are frequently beneficial to parasites, two trematode species may compete for successful transmission through alteration of host phenotypes.     

Diversity of trematode genetic clones within amphipods and the timing of same-clone infections

The genetic diversity of trematodes within second intermediate hosts has important implications for the evolution of trematode populations as these hosts are utilized after the parasites reproduce asexually within first intermediate hosts and before sexual reproduction within definitive hosts. We characterised the genetic clonal diversity of the marine trematode Maritrema novaezealandensis within amphipod (Paracalliope novizealandiae) second intermediate hosts using four to six microsatellite loci to determine if multiple copies of identical trematode clones existed within naturally infected amphipods. To determine the relative timing of infections by identical clones within hosts, trematode metacercariae were assigned to six developmental stages and the stages of identical clones were compared. The genotypes of 306 trematodes were determined from 44 amphipods each containing more than one trematode. Six pairs of identical trematode clones were recovered in total (representing five amphipods: 11% of amphipods with greater than one trematode) and all pairs of clones belonged to the same developmental stage. This suggests that identical clone infections are effectively synchronous. A general decrease in the number of metacercariae recovered, prevalence, and mean intensity of infection for each subsequent developmental stage coupled with large numbers of metacercariae (>9) only being recovered from recent infections, supports the occurrence of post-infection amphipod mortality and/or within-host trematode mortality. Taken together, our results indicate that natural infections are characterised by high genetic diversity, but that amphipods also periodically encounter "batches" of genetically identical clones, potentially setting the stage for interactions within and between clonal groups inside the host.     

Seasonal dynamics of the trematodes fauna in herring gull (Larus argentatus Pontopp.) of Kola Bay

Trematode fauna of the herring gulls from Kola Bay (Barents Sea) was investigated in March, May, June, and September 2005. The data on the trematode species composition and indices of the invasion of gulls with trematodes are given for each season. It was established, that trematode species composition is increased from spring to summer, and intensity of the gulls' invasion with some trematode species is increased from summer to autumn. Ecological factors causing seasonal differences of the trematode fauna in gulls are discussed.     

The role of spatial and temporal heterogeneity and competition in structuring trematode communities in the great pond snail, Lymnaea stagnalis (L.)

We assessed how spatial and temporal heterogeneity and competition structure larval trematode communities in the pulmonate snail Lymnaea stagnalis . To postulate a dominance hierarchy, mark-release-recapture was used to monitor replacements of trematode species within snails over time. In addition, we sampled the trematode community in snails in different ponds in 3 consecutive years. A total of 7,623 snails (10,382 capture events) was sampled in 7 fishponds in the Jind?ich?v Hradec and T?eboň areas in South Bohemia (Czech Republic) from August 2006 to October 2008. Overall, 39% of snails were infected by a community of 14 trematode species; 7% of snails were infected with more than 1 trematode species (constituting 16 double- and 4 triple-species combinations). Results of the null-model analyses suggested that spatial heterogeneity in recruitment among ponds isolated trematode species from each other, whereas seasonal pulses in recruitment increased species interactions in some ponds. Competitive exclusion among trematodes led to a rarity of multiple infections compared to null-model expectations. Competitive relationships among trematode species were hypothesized as a dominance hierarchy based on direct evidence of replacement and invasion and on indirect evidence. Seven top dominant species with putatively similar competitive abilities (6 rediae and 1 sporocyst species) reduced the prevalence of the other trematode species developing in sporocysts only.     

Spatial and temporal variations in the trematode component community of the mudsnail Hydrobia ventrosa in relation to the occurrence of waterfowl as definitive hosts

The component community of larval trematodes infecting the mudsnail Hydrobia ventrosa (Montagu) was examined in coastal lagoons of the southern Baltic Sea among different host subpopulations in relation to the structure of the waterfowl community. The 10 trematode species observed represent the families Notocotylidae (1), Echinostomatidae (1 or 2), Heterophyidae (2). Monorchidae (1). Microphallidae (3 or 4), Psilostomatidae (1), and Hemiuridae (1). Eight of these species infect waterfowl as adults. The structure of the trematode communities was similar between sampling sites. Seven trematode taxa were commonly found at all sampling sites. Prevalence values of the 6 most abundant taxa, which infect birds as final hosts, were significantly different between neither sampling sites nor across year. Overall trematode prevalence in H. ventrosa fluctuated seasonally. Prevalence usually peaked in summer between July and September or October. Low prevalences were observed in late winter and early spring. In contrast, the seasonal maximum in waterfowl numbers differed between areas because of significant spatial differences in the bird community structure. The species composition of the component trematode community of H. ventrosa in the coastal lagoons of the southern Baltic Sea is more or less independent of the species composition of the waterfowl community. This independence presumably results from the lack of host specificity in most of the observed trematode species. Otherwise, the low host specificity in combination with the enormous waterfowl diversity in the coastal lagoons might explain the stability of the prevalence pattern of the component trematode community.     

Intermediate host of the trematode Quinqueserialis quinqueserialis (Trematoda, Notocotylidae) in the USSR and the morphology of its parthenitae and larvae

A high infection rate of muskrat with the trematode Q. quinqueserialis was recorded in Pribaikalje. Its intermediate host is the mollusc Gyraulus (Anisus) stroemi. Morphology and biology of parthenites and larval phases of the development are studied and characters of the biology of this trematode are found out.     

Component community dynamics of larval trematodes in the freshwater snail Semisulcospira nakasekoae in the Uji River, central Japan

The component community of larval trematodes in the freshwater snail Semisulcospira nakasekoae (Caenogastropoda: Sorbeoconcha: Pleuroceridae) was surveyed over 13 months from April 1996 to April 1997 inclusive. Temporal and spatial fluctuation of trematode prevalence, the frequency of multiple infections, and the duration of cercarial shedding were examined as factors that might affect trematode community structure. The spatial prevalence of some species varied significantly, but the dynamics were too small to allow an explanation of the overall pattern. The prevalence of sanguinicolids fluctuated temporally, despite a stable size distribution in the host populations (> 6.0 mm shell width), suggesting the life-cycle phenology of this species. Some pairs of species had statistically positive associations, but no pairs had negative associations. This shows the importance of positive association possibly as a result of suppression of the host defensive response on trematode community structures in molluscan hosts. The length of the patent period, which is part of the persistent period, varied among trematode species, suggesting it to be one of the factors determining prevalence in the host population.     

The biology of the trematode Echinochasmus milvi under the southern conditions of the Far East

The biology of the trematode Echinochasmus milvi Yamaguti, 1939 under the conditions of the southern Far East of the USSR is studied. The development of the trematode proceeds with the participation of intermediate hosts, molluscs of the genus Juga, additional hosts, freshwater fishes, and definitive hosts, fish-eating birds and mammals, and is completed at a temperature of 17 to 23 degrees within 21 weeks.     

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.     

Host diversity and latitude drive trematode diversity patterns in the European freshwater fauna

Aim We investigated the relationship between host and parasite diversity as well as latitudinal gradients in parasite diversity on a continental scale in European freshwater trematodes. Location European freshwaters. Methods We extracted distributional data for 564 freshwater trematodes across 25 biogeographical regions in Europe from the Limnofauna Europaea and used multiple regression analyses to test for correlations between the diversity of definitive (vertebrates) or first intermediate (gastropods) hosts and that of trematodes, and for latitudinal gradients in trematode diversity. In particular, we investigated patterns in beta diversity among latitudinal bands and between trematode species that parasitize host groups with low (autogenic) and high (allogenic) dispersal capacity. We also tested for a latitudinal gradient in the proportional representation of these two trematode groups within regional faunas. Results Latitude or first intermediate host richness had no effect on trematode richness, but definitive host richness was a strong predictor of trematode richness, among both allogenic and autogenic parasites. We found that beta diversity of trematode faunas within latitudinal bands decreased to the north, with similar values for allogenic and autogenic trematodes. Finally, we observed an increasing proportion of autogenic species toward the north of Europe. Main conclusions The richness of definitive hosts appears to be the driver of trematode diversity at a continental scale. The latitudinal gradient in beta diversity reflects patterns observed in free‐living species and probably results from recolonization in the aftermath of the ice ages. The similar beta‐diversity patterns of allogenic and autogenic trematodes and the increasing proportion of autogenic trematodes with increasing latitude are surprising. We suggest that the geographical scale of our analysis or confounding factors such as differences in habitat utilization and specialization may partly explain these patterns.     

Elevated female fecundity as a possible compensatory mechanism in response to trematode infestation in populations of Littorina saxatilis (Olivi)

Co-evolution between parasites and their hosts may lead to changes in the life-history traits of the host that promote sustainability of their populations despite parasite pressure. Such changes are expected to be especially pronounced in the host-parasite systems where parasites cause complete castration of their hosts. We have studied populations of the rough periwinkle, Littorina saxatilis, infested by castrating trematode species, in order to determine whether high infestation levels are associated with a compensatory increase in host fecundity. To test this hypothesis, we determined female fecundity in populations with trematode prevalence spanning from <1% to 30-75%, and followed long-term changes in female fecundity and trematode infestation in two heavily infested populations of L. saxatilis. The broad-scale geographic analysis of populations with different trematode burdens showed that fecundity of uninfected females is significantly higher in highly infested L. saxatilis populations than in those with low trematode burdens. This is also supported by a comparison of fecundity in two pairs of geographically adjacent populations with contrasting trematode levels, revealing higher fecundity of uninfected females in heavily infested populations. Higher fecundity could be explained by the larger size of uninfected females in some heavily infested populations but not in others. Long-term (15-20 years) intra-population analysis performed in two heavily infested L. saxatilis populations showed that female fecundity increased in parallel with a long-term increase in trematode prevalence from 20% to >75% in one population, but remained high and relatively stable in the second population, reflecting its consistently high trematode prevalence (40-65%). These data support the hypothesis that an increase in female fecundity may be a population compensation mechanism in response to heavy trematode infestation in L. saxatilis and suggest the possible involvement of both natural selection and fast (physiological) regulation mechanisms.     

Environmental factors influencing community composition of gastropods and their trematode parasites in southern Ontario

Agricultural activity and landscape features have previously been associated with diversity and prevalence of trematode species in amphibian second intermediate hosts. In this study, the density, diversity, and size of snail first intermediate hosts, and the diversity and prevalence of their trematode species, were assessed in 2 types of ponds, i.e., those adjacent to cornfields and those from the same region in southwestern Ontario that were adjacent to nonagricultural settings. Species of trematodes included, but were not restricted to, those that are known parasites of larval and adult frogs. We also assessed landscape factors likely to influence use by definitive hosts. Presence of the herbicide atrazine in ponds was measured to check that ponds adjacent to agriculture had potential to be affected by agricultural runoff. Both snail size and the proportion of snails releasing cercariae were greater in nonagricultural ponds, contrasting with a previous finding of lower trematode infection in tadpoles from nonagricultural ponds. Percentage of forest cover was associated with prevalence of certain trematode species, but not with estimates of combined prevalence. Absence of relations of trematode prevalence to measures of road density also contrasted with previous studies. We interpret our results in light of how agricultural activity might influence trematode viability, snail growth, and use by wildlife definitive hosts, independently of landscape factors.     

Mitochondrial respiratory activity of the trematode Fasciola hepatica

Polarographic studies have been made on the respiratory activity of isolated mitochondria of the trematode F. hepatica. Respiratory chain transferring electrons to oxygen and which is sensitive to cyanide was found in the mitochondria. Certain coupling between respiration and phosphorylation was observed. Intact mitochondria of the trematode exhibit the respiratory control although its level is significantly lower than that in the mitochondria from rat liver. The existence of an alternative respiratory chain was demonstrated in which electron transport is not associated with ATP synthesis.     

Environmental factors influencing trematode prevalence in grey tree frog (Hyla versicolor) tadpoles in southern Ontario

The emergence or increased prevalence of various parasites may be linked to alterations in host-parasite interactions caused by environmental changes. We investigated prevalence of trematode infections in grey tree frog (Hyla versicolor) tadpoles from ponds in nonagricultural settings versus ponds adjacent to cornfields in southern Ontario. We found that agricultural activity was a significant factor in determining the percentage of tadpoles infected by 1 or more trematodes from 1 or more species (combined trematode infection). However, we found no associations between combined trematode infection and forest cover; pond size; road density; and measures of water quality, such as nitrate level and the presence of the herbicide atrazine. Although combined trematode prevalence was associated only with agricultural activity, prevalence of Alaria species showed a positive association with forest cover. This latter result probably reflects the importance of habitat suitability for the canid definitive hosts of this trematode species.     

New trematode species from commercial fish of the Indian Ocean

New for the science three trematode species are described--Aporocotyle nototheniae sp. nov., Prosorchis saicevi sp. nov., Pseudocardicola emmelichthy sp. nov.--from commercial fishes of the Indian Ocean. New genus Pseudocardicola gen. nov. and new subfamily Pseudocardicolinae subfam. nov. are substantiated for Pseudocardicola emmelichthy species. The differential diagnoses for all three trematode species are given.     

Meningoencephalitis in two stranded California sea lions (Zalophus californianus) caused by aberrant trematode migration

Meningoencephalitis caused by aberrant trematode migration is described in two California sea lions (Zalophus californianus) admitted to a rehabilitation hospital between May and August 2001. Both animals displayed seizure activity and were euthanized due to poor response to therapy. Gross abnormal findings included liver flukes (Zalophotrema hepaticum) in the bile ducts and areas of swelling and necrosis in the cerebrum, cerebellum, and brain stem. Histopathology revealed meningoencephalitis with necrosis, hemorrhage, and many trematode eggs within the brain. In one sea lion, an adult trematode was found on the surface of the cerebrum. These are believed to be the first reported cases of meningoencephalitis caused by aberrant trematode migration in pinnipeds.     

Patterns and consequences of behavioural responses to predators and parasites in Rana tadpoles

We examined the interactive effects of predators and trematodes on Rana sybatica and Rana clamitans larvae. We hypothesized that exposure to predators would increase tadpole susceptibility to trematode infection, by reducing tadpole activity and thereby increasing time spent on the bottom. We further hypothesized that the tadpoles would experience reduced rates of growth and development in the presence of either predators or parasites, and that predator presence would stimulate both species to develop larger tails and smaller bodies. Rana clamilans and R. sybatica reduced their activity in the presence of both predators and trematode cercariae. In the longer running R. clamitans experiment, predator-exposed tadpoles developed significantly shallower tails and wider bodies, while trematode infection had no effect on growth, development, or shape. Most significantly, we found that extended exposure to caged fish predators made R. clamitans tadpoles more susceptible to trematode infection. A possible mechanism for this increased vulnerability is that reduced activity in the presence of predators increases tadpoles' proximity to cercariae. Our study suggests that various factors that decrease tadpole activity–predator presence, trematode cercariae and certain pesticides–may act synergistically to negatively impact tadpole populations.     

Neorickettsia risticii is vertically transmitted in the trematode Acanthatrium oregonense and horizontally transmitted to bats

Potomac horse fever is known to be transmitted through the ingestion of caddisflies parasitized with Neorickettsia (formerly Ehrlichia) risticii-infected metacercaria. However, the species of trematode involved and how N. risticii is maintained in nature are unknown. In this study, gravid trematodes were recovered from the intestines of 12 out of 15 Eptesicus fuscus big brown bats and eight out of nine Myotis lucifugus little brown bats from various sites in Pennsylvania, USA. Trematode specimens isolated from six E. fuscus bats contained N. risticii DNA. The trematode was identified as Acanthatrium oregonense. N. risticii was detected within individual trematode eggs by polymerase chain reaction as well as by immunofluorescence labelling with an anti-N. risticii antibody, indicating that N. risticii is vertically transmitted (from adult to egg) in A. oregonense. Furthermore, N. risticii DNA was detected in the blood, liver or spleen of 23 out of 53 E. fuscus and M. lucifugus bats, suggesting that N. risticii can also be transmitted horizontally from trematode to bat. These results indicate that A. oregonense is a natural reservoir and probably a vector of N. risticii.     

Trematode fauna patterns of the freshwater fish on the border of the geographical range

The trematode fauna of the fishes inhabiting Lake Ladoga are represented by forty-six species; nine species of which are found here on the northern boudary of their geographic range. The depauperization of the trematode fauna compared to the southern pools is a result both of the decreasing impact of the Pont-Caspian group and of the introduction of the boreal piedmont species complex. The increase in the biological productivity of Lake Ladoga for the last 50-year period leads to enrichment of the species biodiversity. The same process increases the invasion extensiveness by trematodes, which use fish as an intermediate host. The Diplostomida, the presence of which is crucial for the young fish survival rate, dominate among the trematodes.