Narrower isotopic niche size in fish infected by the intestinal parasite Pomphorhynchus sp. compared to uninfected ones

Examples of parasite-related effects on intermediate crustacean hosts are numerous but their ecological consequences on their vertebrate hosts are scarce. Here, we address the role of macroparasite infections on the trophic niche structure of definitive hosts and its potential physiological consequences using wild fish populations infected with an acantochephalan parasite Pomphorhynchus sp., a trophically transmitted intestinal worm. Infected and uninfected fish were sampled from six populations on the Marne River, France and the prevalence of intestinal parasites in the host populations ranged from 50% to 90%. Although the isotopic ratios (δ¹³ C and δ¹⁵ N) did not differ between infected and uninfected fish, we found a consistent pattern of isotopic niche size being considerably smaller in infected hosts when compared with noninfected ones. This was not explained by interindividual differences in intrinsic factors such as length/age or body condition between infected and uninfected fish. These results suggest a potential niche specialization of infected fish, which did not impair their energetic status.

Parasite infection influences the biomarker response and locomotor activity of Gammarus fossarum exposed to conventionally-treated wastewater

Modern wastewater treatment plants cannot completely remove pollutants. Often, effluents entering the aquatic environment still contain micropollutants such as pharmaceuticals or pesticides, which may impose adverse effects on aquatic biota. At the same time, a large proportion of free-living aquatic species are known to be infected with parasites, which raises the question of interactions between environmental stressors (such as micropollutants) and parasite infection. We chose the freshwater amphipod Gammarus fossarum (Koch, 1835) as a test organism to investigate potential pollutant-parasite interactions. This gammarid is frequently used in ecotoxicological tests and is also commonly infected with larvae of the acanthocephalan parasite species Polymorphus minutus (Zeder, 1800) Lühe, 1911. We exposed infected and uninfected specimens of G. fossarum to conventionally-treated wastewater and river water in a 22-day flow channel experiment. The test organisms' response was measured as mortality rates, concentrations or activities of five biomarkers, and overall locomotor activity. No significant differences were found between mortality rates of different exposure conditions. Contrastingly, three biomarkers (phenoloxidase activity, glycogen, and lipid concentrations) showed a significant increase in infected gammarids, while the effect of the water type was insignificant. Infected gammarids also showed a significantly higher locomotor activity in both water types. Our results suggest that the response of G. fossarum during the exposure experiments was mainly driven by parasite infection. This implies that parasites may act as additional biotic stressors in multiple stressor scenarios, and therefore, might play an important role when measuring the response of organisms to chemical stressors. Future ecotoxicological studies and assessments thus should consider parasite infection as an additional test parameter.

The phylogeographic puzzle of Pseudoacanthocephalus toshimai, an amphibian acanthocephalan in northern Japan

The amphibian acanthocephalan, Pseudoacanthocephalus toshimai, was considered to be an island-endemic species in Hokkaido, Japan. However, the parasite was found from Rana ornativentris, Rana tagoi, Zhangixalus arboreus, and Bufo japonicus formosus in northern Honshu (Aomori and Iwate Prefectures), which is separated from Hokkaido by the Tsugaru Strait. The mitochondrial DNA-based phylogenetic and population genetic analyses of P. toshimai showed that the northern Honshu isolates are far distantly related to the Hokkaido isolates, and that a demographic population expansion occurred in Hokkaido during the recent geological past. The rich genetic diversity of P. toshimai in northern Honshu suggests a scenario that anuran hosts invaded Hokkaido together with P. toshimai via the land bridge of the Tsugaru Strait. However, the evolutionary history of Rana pirica, a main definitive host for P. toshimai in Hokkaido, is contradictory to the introduction scenario inferred from the parasite. The finding of several geographically mismatched isolates of P. toshimai from both northern Honshu and Hokkaido suggests a possibility that the migration of the parasite infrequently occurred between the two areas even after the land bridge disappeared. More detailed information on the evolutionary history of anurans is needed to resolve the biogeographical enigma of P. toshimai.

Taxonomic resolution affects host-parasite association model performance

Identifying the factors that structure host–parasite interactions is fundamental to understand the drivers of species distributions and to predict novel cross-species transmission events. More phylogenetically related host species tend to have more similar parasite associations, but parasite specificity may vary as a function of transmission mode, parasite taxonomy or life history. Accordingly, analyses that attempt to infer host−parasite associations using combined data on different parasite groups may perform quite differently relative to analyses on each parasite subset. In essence, are more data always better when predicting host−parasite associations, or does parasite taxonomic resolution matter? Here, we explore how taxonomic resolution affects predictive models of host−parasite associations using the London Natural History Museum's database of host–helminth interactions. Using boosted regression trees, we demonstrate that taxon-specific models (i.e. of Acanthocephalans, Nematodes and Platyhelminthes) consistently outperform full models in predicting mammal-helminth associations. At finer spatial resolutions, full and taxon-specific model performance does not vary, suggesting tradeoffs between phylogenetic and spatial scales of analysis. Although all models identify similar host and parasite covariates as important to such patterns, our results emphasize the importance of phylogenetic scale in the study of host–parasite interactions and suggest that using taxonomic subsets of data may improve predictions of parasite distributions and cross-species transmission. Predictive models of host–pathogen interactions should thus attempt to encompass the spatial resolution and phylogenetic scale desired for inference and prediction and potentially use model averaging or ensemble models to combine predictions from separately trained models.

Trophic relationship between the Patinga hybrid (Piaractus mesopotamicus x Piaractus brachypomus) and Echinorhynchus gomesi Machado Filho, 1948 in fish farms

A total of 122 Patinga specimens were collected from fish farms (P1, P2 and P3), and only those from fish farm P1 were shown to be infected with Echinorhynchus gomesi. In addition, fish in this study were shown to have diets that consisted of 21 different food items, and Notodiaptomus sp. (Copepoda: Calanoida) was identified as a potential intermediate host for E. gomesi.

Trade-Offs with Growth Limit Host Range in Complex Life-Cycle Helminths

AbstractParasitic worms with complex life cycles have several developmental stages, with each stage creating opportunities to infect additional host species. Using a data set for 973 species of trophically transmitted acanthocephalans, cestodes, and nematodes, we confirmed that worms with longer life cycles (i.e., more successive hosts) infect a greater diversity of host species and taxa (after controlling for study effort). Generalism at the stage level was highest for middle life stages, the second and third intermediate hosts of long life cycles. By simulating life cycles in real food webs, we found that middle stages had more potential host species to infect, suggesting that opportunity constrains generalism. However, parasites usually infected fewer host species than expected from simulated cycles, suggesting that generalism has costs. There was no trade-off in generalism from one stage to the next, but worms spent less time growing and developing in stages where they infected more taxonomically diverse hosts. Our results demonstrate that life-cycle complexity favors high generalism and that host use across life stages is determined by both ecological opportunity and life-history trade-offs.

Increased temperature has no consequence for behavioral manipulation despite effects on both partners in the interaction between a crustacean host and a manipulative parasite

Parasites alter many traits of their hosts. In particular, parasites known as "manipulative" may increase their probability of transmission by inducing phenotypic alterations in their intermediate hosts. Although parasitic-induced alterations can modify species' ecological roles, the proximate factors modulating this phenomenon remain poorly known. As temperature is known to affect host-parasite associations, understanding its precise impact has become a major challenge in a context of global warming. Gammarids are ecologically important freshwater crustaceans and serve as intermediate hosts for several acanthocephalan species. These parasites induce multiple effects on gammarids, including alterations of their behavior, ultimately leading to modifications in their functional role. Here, experimental infections were used to assess the effect of two temperatures on several traits of the association between Gammarus pulex and its acanthocephalan parasite Pomphorhynchus laevis. Elevated temperature affected hosts and parasites in multiple ways (decreased host survival, increased gammarids activity, faster parasites development and proboscis eversion). However, behavioral manipulation was unaffected by temperature. These results suggest that predicted change in temperature may have little consequences on the trophic transmission of parasites through changes in manipulation, although it may modify it through increased infection success and faster parasites development.

Ecotoxicoparasitology of mercury and trace elements in semi-aquatic mammals and their endoparasite communities

Many contaminants persist in the environment for decades or more, influencing ecosystem health. Environmental contamination with mercury (Hg) is a particular concern due to its ability to biomagnify in food webs and its lethal and sub-lethal effects in exposed organisms. Despite the known impacts of anthropogenic contamination, there remains a need for data on wildlife exposure to Hg and other contaminants, and the effects of exposure on wildlife health. The objectives of this study were to: 1) quantify differences in concentrations of mercury and other trace elements among three sympatric semiaquatic mammals of different assumed trophic position: North American river otter (Lontra canadensis), raccoon (Procyon lotor), and North American beaver (Castor canadensis), 2) compare trace element concentrations between animals captured on the Savannah River Site (SRS) in South Carolina, USA, where known inputs of Hg and other trace elements have occurred, and reference sites in South Carolina (SC) and Georgia (GA), USA, and 3) investigate the relationship between host trace element concentrations and endoparasite communities. River otters, beavers, and raccoons were sampled from the SRS, SC, and GA to quantify trace element concentrations in liver tissue and quantify endoparasite communities. Both species and sampling location were important factors determining hepatic trace element concentration, however, there was no consistent trend of elevated trace element concentrations among animals sampled on the SRS. Only Hg demonstrated biomagnification based on assumed trophic position, with river otters having the highest Hg concentrations among the sampled species. Additionally, the results suggest a possible relationship between host hepatic mercury concentration and endoparasite abundance, while hepatic selenium concentration may be related to endoparasite diversity. These findings further demonstrate how wildlife can accumulate anthropogenic contamination, although future research is needed to determine the mechanisms contributing to patterns observed between endoparasite communities and the contaminant concentrations of their mammalian hosts.

The digestive tube of Piaractus brachypomus: gross morphology, histology/histochemistry of the mucosal layer and the effects of parasitism by Neoechinorhynchus sp

The objective of the present study was to describe the histology and histochemistry of the mucosal layer of the digestive tube of Piaractus brachypomus, and the histopathology associated with parasitism by Neoechinorhynchus sp. The digestive tube of P. brachypomus consists of three macroscopically distinct portions: short, rectilinear and elastic-walled ooesophagus, J-shaped siphon stomach and a long intestine with rectilinear and curved portions, defined by patterns of villi as foregut, midgut, and hindgut. Histological and histochemical differences were observed in the mucosal layers of the different digestive tube regions, such as intense production of neutral and acidic mucous substances in the pseudostratified mucosal epithelium of the oesophagus; positive periodic acid Schiff reagent (PAS)reactions at the apex of the columnar epithelial cells of the stomach and increased intensity of histochemical reactions in the hindgut region. Neoechinorhynchus sp. was present in 85.7% of specimens examined, with a mean intensity of 7.4 ± 6.2 (±) and abundance of 6.33. Good health of the fish indicated by high relative condition factor values ( _Kn ) and occurrence of only mild to moderate alteration in the mucosal layer indicated that Neoechinorhynchus sp. exhibits low pathogenicity towards P. brachypomus hosts in farming environments, with low levels of infection.

Decreased Metabolic Rate in the Mole Crabs, Emerita analoga, Infected with the Acanthocephalan Profilicollis altmani

The relationship between a parasite and its host will have an energy cost for the host at some point; however, this basic hypothesis has seldom been evaluated. Using Emerita analoga as a model species, we investigated the aerobic metabolism, ammonia excretion rate, and locomotor performance patterns of crabs both uninfected and infected with the acanthocephalan Profilicollis altmani. Our results show that infected Emerita had a lower metabolic rate compared to uninfected ones. Whether or not this decrease is a result of the pathology of the parasite infection or due to manipulation of the host by the parasite is still unknown. We discuss the importance of using anaerobic and aerobic metabolism and more-complex scenarios in order to understand the effects on host fitness and not only on the immediate response of the host.

The development of Neoechinorhynchus buttnerae (Eoacanthocephala: Neoechinorhynchidae) in its intermediate host Cypridopsis vidua in Brazil

The family Neoechinorhynchidae includes seven species of Neoechinorhynchus from freshwater fishes of Brazil. Although several Neoechinorhynchus species are cited infecting different fish species in Brazil, there is a lack of information concerning to their life cycle and the identification of the intermediate hosts. Thus, the aim of the present study was to describe the development of Neoechinorhynchus buttnerae in its intermediate host collected in a fish farm located in Rio Preto da Eva, Amazonas, Brazil. To verify the presence of N. buttnerae in the fish pond, twenty Colossoma macropomum were captured and analyzed, being corroborated the presence of this parasite species. Samples of plankton were also collected, finding the ostracod Cypridopsis vidua as the intermediate host. For the description of the larvae development, a laboratory experimental procedure was conducted by feeding the collected ostracods with the eggs of the adult specimens taken from the sampled fish. To observe the stages of development an artificial hatch was performed. Every stage of development was photographed, measured, drawn and described. The time of development of the immature stages of N. buttnerae was 29 days, reporting the stages: acanthor, acanthella (with eight developmental changes) and cystacanth. As high infections by N. buttnerae causes morphological damages to the intestine and may compromise the quality of C. macropomum and in consequence the production of fish farmers in the Brazilian Amazon region, the knowledge of its intermediate host and the understanding of its life cycle represents a useful information to prevent and combat infections by this parasite.

Histopathological and ultrastructural assessment of two mugilid species infected with myxozoans and helminths

The histopathology and ultrastructure of the intestine of mullets, Liza ramada and Liza saliens, from Comacchio lagoons (northern Italy) naturally infected with myxozoans and helminths were investigated and described. Sixty-two (80.5%) of 77 mullets harboured one or more of the following parasites species: Myxobolus mugchelo (Myxozoa), Neoechinorhynchus agilis (Acanthocephala), Haplosplanchnus pachysomus and Dicrogaster contractus (Digenea). Co-occurrence of helminths with myxozoans was common. The main damage caused by digeneans was destruction of the mucosal epithelium of the villi, necrosis and degeneration of intestinal epithelial cells. More severe intestinal damage was caused by acanthocephalans which reach the submucosa layer with their proboscis. At the site of helminths infection, several mast cells (MCs), rodlet cells (RCs), mucous cells and few neutrophils and macrophages were observed in the epithelium. RCs and mucous cells exhibited discharge activity in close vicinity to the worm's tegument. M. mugchelo conspicuous plasmodia were encysted mainly in muscle and submucosa layers of the intestine. Indeed, spores of M. mugchelo were documented within the epithelial cells of host intestine and in proximity to MCs. Degranulation of the MCs near the myxozoans was very frequent.

Protective responses of intestinal mucous cells in a range of fish-helminth systems

Histopathological, immunofluorescence and ultrastructural studies were conducted on the intestines of four fish species infected with different taxa of enteric helminths. Brown trout (Salmo trutta trutta), eel (Anguilla anguilla) and tench (Tinca tinca) obtained from Lake Piediluco (central Italy) were examined. Brown trout and eel were infected with two species of acanthocephalans, and tench was parasitized with a tapeworm species. In addition to the above site, specimens of chub (Squalius cephalus) and brown trout infected with an acanthocephalan were examined from the River Brenta (north Italy). Moreover, eels were examined from a brackish water, Comacchio lagoons (north Italy), where one digenean species was the predominant enteric worm. All the helminths species induced a similar response, the hyperplasia of the intestinal mucous cells, particularly of those secreting acid mucins. Local endocrine signals seemed to affect the production and secretion of mucus in the parasitized fish, as worms often were surrounded by an adherent mucus layer or blanket. This is the first quantitative report of enteric worm effects on the density of various mucous cell types and on the mucus composition in intestine of infected/uninfected conspecifics. We provide a global comparison between the several fish-helminth systems examined.

The discovery of acanthocephalans parasitizing chaetognaths

A comprehensive literature review shows that 12 types of pathogens, micropredators and parasites are reported to interact with chaetognaths, mostly digenean trematodes, cestodes and nematodes larval stages. Through analysis of 78,152 chaetognaths from a monthly zooplankton time series (Jan 1996-Dec 1998) collected in the Mexican Central Pacific twelve acanthocephalan larvae parasitizing chaetognaths were discovered. This is the first record of an acanthocephalan parasitizing chaetognaths, raising to 13 the types of symbionts known to interact with them (excluding predators). Cystacanth larval specimens of Corynosoma sp. (Polymorphidae) were observed parasitizing the head, trunk and caudal cavities of three of the eight chaetognath species inhabiting this tropical coastal region (Flaccisagitta enflata, Flaccisagitta hexaptera and Zonosagitta bedoti). Because Corynosoma sp. parasitized chaetognaths during different months and years (Jan-Feb 1996, Mar and Jul 1997, Jan, Jun, Aug-Sep 1998) and because the total length of these cystacanths varied between 165-480 µm, suggesting growth inside the hosts, we conclude that chaetognaths are intermediate hosts of Corynosoma sp. The twelve parasitized chaetognaths were juveniles (without gonads) or immature adults (none in reproductively mature stage IV); therefore Corynosoma may have a negative influence on host reproduction. Marine crustaceans (amphipods, decapods, copepods, mysids and euphausiids) and fishes are common intermediate or paratenic hosts of acanthocephalans. Fish, sea birds and marine mammals are definitive hosts for marine Corynosoma species. The present discovery implies that acanthocephalans are transmitted trophically through different intermediate hosts (crustaceans, chaetognaths and/or fish); thus chaetognaths can also be part of the marine acanthocephalan life cycle.

Temperature-related Intraspecific Variability in the Behavioral Manipulation of Acanthocephalan Parasites on Their Gammarid Hosts

Understanding the effect of temperature on ecologically important species has become a major challenge in the context of global warming. However, the consequences of climate change cannot be accurately predicted without taking into consideration biotic interactions. Parasitic infection, in particular, constitutes a widespread biotic interaction, and parasites impact their hosts in multiple ways, eventually leading to consequences for communities and ecosystems. We explored the effect of temperature on the anti-predator behavior of a keystone freshwater invertebrate, the amphipod Gammarus fossarum. Gammarids regularly harbor manipulative acanthocephalan parasites that modify their anti-predator behavior in ways that potentially increase the probability of trophic transmission to their definitive hosts. We investigated the impact of temperature on gammarids infected by two acanthocephalan parasites, Pomphorhynchus tereticollis and Polymorphus minutus. Uninfected and naturally infected gammarids were acclimatized to different temperatures, and their behavior was measured. Our results showed that the effect of infection on the phototaxis of gammarids increased with increasing temperature, with a stronger effect induced by P. tereticollis. In contrast, temperature had no effect on the alteration of refuge use or geotaxis observed in infected gammarids. Our results provide the first direct evidence that temperature can affect the extent of behavioral alteration brought about by certain parasite species. However, the consequences of increased trophic transmission remain elusive; the supposedly key anti-predatory behavior was not significantly affected by exposure of gammarids to different temperatures.

[Infection of the pacific saury Cololabis saira by acanthocephalans in the Kuril Islands area]

The Pacific saury Cololabis saira (Brevoort, 1856) is one of the important target species of commercial fisheries. Food manufacturers and consumers encounter problems due to the infection of the saury by acanthocephalans, which are quite difficult to clean out completely during on-board catch processing. Infection of C. saira was not studied on a regular basis, therefore, our knowledge about the parasites of saury is fragmentary. This paper contains infection indices (only acanthocephalans) of the Pacific saury caught in the Kuril Islands area (Russian Exclusive Economic Zone) in 2015.

[FIRST RECORD OF RHADINORHYNCHUS COLOLABIS (ACANTHOCEPHALA: RHADINORHYNCHIDAE) FROM THE CHERRY SALMON IN THE SEA OF JAPAN]

Drawing, description and characteristics of Rhadinorhynchus cololabis, registered for the first time from Oncorhynchus masou in the Sea of Japan (northern part of Primorye Territory) are given. Ten species of acanthocephalans from the cherry salmon in the Primorsky Territory were recorded.

[ECOLOGICAL AND PARASITOLOGICAL CHARACTERISTICS OF THE SMALL REDFISH SEBASTES VIVIPARUS (PISCES: SCORPAENIDAE)]

The results of the parasite fauna research represent peculiarities of formation and ecological, faunistic and zoogeographical characteristics of parasite fauna of the small redfish Sebastes viviparus Krayer. 1845. This species is distinguished among the other North Atlantic Sebastes by the richest fauna of myxosporidians, trematodes, nematodes and acanthocephalans. The parasite fauna of S. viviparus is formed mainly of boreal species and to a lesser extent of Arctic-boreal species. According to the vertical zonality of parasites in fishes of the North Atlantic they are mainly represented by mesobenthic and epicontinental species. The parasite fauna in small redfish possesses significantly more pronounced geographic specificity than that of other North Atlantic Sebastes species.

Development and Validation of a Biodynamic Model for Mechanistically Predicting Metal Accumulation in Fish-Parasite Systems

Because of different reported effects of parasitism on the accumulation of metals in fish, it is important to consider parasites while interpreting bioaccumulation data from biomonitoring programmes. Accordingly, the first step is to take parasitism into consideration when simulating metal bioaccumulation in the fish host under laboratory conditions. In the present study, the accumulation of metals in fish-parasite systems was simulated by a one-compartment toxicokinetic model and compared to uninfected conspecifics. As such, metal accumulation in fish was assumed to result from a balance of different uptake and loss processes depending on the infection status. The uptake by parasites was considered an efflux from the fish host, similar to elimination. Physiological rate constants for the uninfected fish were parameterised based on the covalent index and the species weight while the parameterisation for the infected fish was carried out based on the reported effects of parasites on the uptake kinetics of the fish host. The model was then validated for the system of the chub Squalius cephalus and the acanthocephalan Pomphorhynchus tereticollis following 36-day exposure to waterborne Pb. The dissolved concentration of Pb in the exposure tank water fluctuated during the exposure, ranging from 40 to 120 μg/L. Generally, the present study shows that the one-compartment model can be an effective method for simulating the accumulation of metals in fish, taking into account effects of parasitism. In particular, the predicted concentrations of Cu, Fe, Zn, and Pb in the uninfected chub as well as in the infected chub and the acanthocephalans were within one order of magnitude of the measurements. The variation in the absorption efficiency and the elimination rate constant of the uninfected chub resulted in variations of about one order of magnitude in the predicted concentrations of Pb. Inclusion of further assumptions for simulating metal accumulation in the infected chub led to variations of around two orders of magnitude in the predictions. Therefore, further research is required to reduce uncertainty while characterising and parameterising the model for infected fish.

[BIODIVERSITY OF ACANTHOCEPHALANS (ACANTHOCEPHALA) IN FRESHWATER FISHES OF ASIATIC SUB-ARCTIC REGION]

The analysis of taxonomical and ecological diversity of acanthocephalans in fishes of Asiatic sub-Arctic region freshwaters, summarizing changes in modern views on species composition, life cycles, and ecology of background groups of these parasites is given. A priority role of studies provided by O. N. Bauer and his scientific school in organization and development of these aspects of acanthocephalology is demonstrated. Special attention is paid to the assessment of acanthocephalan biodiversity of the genus Neoechinorhynchus, the background group of freshwater fish parasites of the Asiatic sub-Arctic region, and an original key for their species is given. The distribution of acanthocephalans of the genus Acanthocephalus in northeastern Asia is analyzed and prospective study of this parasite group, evolutionary associated with freshwater isopods of the genus Asellus as intermediate hosts, is outlined. The absence of documented evidences on intermediate hosts of other background parasites of freshwater fishes in the region, acanthocephalans of the genus Metechinorhynchus, is revealed. It is assumed that subsequent taxonomic revisions based both on morphological and molecular genetic studies are necessary for the reliable revealing of species composition in each genus of the background acanthocephalans from freshwater fishes of Northern Asia. Theoretical significance of the study of acanthocephalan life cycles and revealing their natural intermediate hosts for the reliable estimation of structural and functional organization of their host-parasite systems in different parts of the range is substantiated and the possibility of the distribution of taxonomic conclusions in new territories is analyzed. A brief annotated taxonomical list of freshwater acanthocephalans of the Asiatic sub-Arctic region is given.

Occurrence of immune cells in the intestinal wall of Squalius cephalus infected with Pomphorhynchus laevis

A sub-population of 34 specimens of chub, Squalius cephalus, was sampled from the River Brenta (Northern Italy) and examined for ecto- and endo-parasites. Pomphorhynchus laevis (Acanthocephala) was the only enteric helminth encountered. Immunofluorescence and ultrastructural studies were conducted on the intestines of chub. Near the site of parasite's attachment, mucous cells, mast cells (MCs), neutrophils and rodlet cells (RCs) were found to co-occur within the intestinal epithelium. The numbers of mucous cells, MCs and neutrophils were significantly higher in infected fish (Mann-Whitney U test, p < 0.05). Dual immunofluorescence staining with the lectin Dolichos Biflorus Agglutinin (DBA) and the macrophage-specific MAC387 monoclonal antibody, with parallel transmission electron microscopy, revealed that epithelial MCs often made intimate contact with the mucous cells. Degranulation of a large number of MCs around the site of the acanthocephalan's attachment and in proximity to mucous cells was also documented. MCs and neutrophils were abundant in the submucosa. Immune cells of the intestinal epithelium have been described at the ultrastructural level and their possible functions and interactions are discussed.

Does fish reproduction and metabolic activity influence metal levels in fish intestinal parasites, acanthocephalans, during fish spawning and post-spawning period?

Application of fish intestinal parasites, acanthocephalans, as bioindicators in metal exposure assessment usually involves estimation of their metal levels and bioconcentration factors. Metal levels in parasite final host, fishes, are influenced by fish physiology but there is no data for acanthocephalan metal levels. Gastrointestinal Zn, Fe, Mn, Cd, Ag levels in European chub (Squalius cephalus L.) from the Sava River were significantly higher during chub spawning (April/May) compared to the post-spawning period (September). In acanthocephalans (Pomphorhynchus laevis and Acanthocephalus anguillae) significantly higher metal levels during chub spawning were observed only for Zn in P. laevis. Bioconcentration factors were twice as high for Fe, Mn, Ag, Pb in the post-spawning period, probably as a consequence of lower gastrointestinal metal levels in fish rather than metal exposure. Therefore, bioconcentration factors should be interpreted with caution, due to their possible variability in relation to fish physiology. In addition, gastrointestinal Cu, Cd and Pb levels were lower in infected than uninfected chub, indicating that metal variability in fishes might be affected by the presence of acanthocephalans.

Corynosomaacanthocephalans in their paratenic fish hosts in the northern Baltic Sea

Cystacanth stages of three Corynosoma (Acanthocephala) species, C. strumosum and C. semerme, and a new species in the Bothnian Bay, C. magdaleni, were studied in the fourhorn sculpin (Myoxocephalus quadricornis) in 1996-1997. The length of the trunk and proboscis differentiated the three species in the fish. The stability of the Corynosoma infection was studied by comparing the present results with those collected from the same areas (central and coastal) in 1977-1982 (Valtonen, 1983a). As C. magdaleni and C. strumosum were not separated at that time, the joint infections of these two species (called "C. strumosum") were compared. The stability of infection with C. semerme in the central Bothnian Bay was noticeable (prevalences were 82.9 in earlier period and 81.9% in later period), while the prevalences of "C. strumosum" in the same areas had decreased (21 and 13.5%, respectively). This is suggested to be due to the disappearance of the marine bull-rout, Myoxocephalus scorpius, from the Bothnian Bay during the 1990s due to an overall decline in salinity throughout the Baltic Sea. In the coastal area Corynosoma infection was clearly lower than in central area in both periods.

Non-specific manipulation of gammarid behaviour by P. minutus parasite enhances their predation by definitive bird hosts

Trophically-transmitted parasites often change the phenotype of their intermediate hosts in ways that increase their vulnerability to definitive hosts, hence favouring transmission. As a "collateral damage", manipulated hosts can also become easy prey for non-host predators that are dead ends for the parasite, and which are supposed to play no role in transmission strategies. Interestingly, infection with the acanthocephalan parasite Polymorphus minutus has been shown to reduce the vulnerability of its gammarid intermediate hosts to non-host predators, whose presence triggered the behavioural alterations expected to favour trophic transmission to bird definitive hosts. Whilst the behavioural response of infected gammarids to the presence of definitive hosts remains to be investigated, this suggests that trophic transmission might be promoted by non-host predation risk. We conducted microcosm experiments to test whether the behaviour of P. minutus-infected gammarids was specific to the type of predator (i.e. mallard as definitive host and fish as non-host), and mesocosm experiments to test whether trophic transmission to bird hosts was influenced by non-host predation risk. Based on the behaviours we investigated (predator avoidance, activity, geotaxis, conspecific attraction), we found no evidence for a specific fine-tuned response in infected gammarids, which behaved similarly whatever the type of predator (mallard or fish). During predation tests, fish predation risk did not influence the differential predation of mallards that over-consumed infected gammarids compared to uninfected individuals. Overall, our results bring support for a less sophisticated scenario of manipulation than previously expected, combining chronic behavioural alterations with phasic behavioural alterations triggered by the chemical and physical cues coming from any type of predator. Given the wide dispersal range of waterbirds (the definitive hosts of P. minutus), such a manipulation whose efficiency does not depend on the biotic context is likely to facilitate its trophic transmission in a wide range of aquatic environments.

Influence of the cestode Ligula intestinalis and the acanthocephalan Polymorphus minutus on levels of heat shock proteins (HSP70) and metallothioneins in their fish and crustacean intermediate hosts

It is a common method to analyse physiological mechanisms of organisms - commonly referred to as biomarkers - to indicate the presence of environmental pollutants. However, as biomarkers respond to a wide range of stressors we want to direct the attention on natural stressors, i.e. on parasites. After two years maintenance under controlled conditions, roach (Rutilus rutilus) revealed no influence on levels of metallothionein by the parasite Ligula intestinalis. The same was found for Gammarus fossarum infected with Polymorphus minutus. However, the heat shock protein (HSP70) response was affected in both host-parasite systems. While the infection of roach resulted in reduced levels of HSP70 compared to uninfected roach, the infection in G. fossarum led to higher levels of HSP70. We also analysed the effect of a 14 days Cd exposure (4 μg/L) on the uninfected and infected gammarids. The exposure resulted in induced levels for both, metallothionein and HSP70 whereas the combination of stressors, parasite and exposure, revealed a decrease for levels of HSP70 in comparison to the metal exposure only. Accordingly, parasites as natural parts of aquatic ecosystems have to be considered in ecotoxicological research.

Nyctiphanes couchii as intermediate host for Rhadinorhynchus sp. (Acanthocephala, Echinorhynchidae) from NW Iberian Peninsula waters

In the mesozooplanktonic community of the coastal upwelling system of the Ría de Vigo (NW Spain), the euphausiid Nyctiphanes couchii has been identified for the first time in temperate waters of the NE Atlantic as the intermediate host for cystacanths of Rhadinorhynchus sp. Parasites were identified using morphological characters described in 20 cystacanths. The hooks of the proboscis were arranged in 14 rows of 26 hooks each, while the hooks of the basal circle were only slightly erected and were longer than remaining spines. A maximum-likelihood estimation (ML) tree inferred from the 18S rRNA data set of Palaeacantocephala revealed that our specimens belong to a highly supported clade with Rhadinorhynchus sp., Pararhadinorhynchus sp. and Transvena annulospinosa. Nonetheless, our morphological and phylogenetic analyses suggested that the status of Rhadinorhynchus pristis should be re-examined. The prevalences of parasites were 0.0019% and 0.0001% for frontal and coastal summer communities, and 0.0068% and 0.0008% for coastal and oceanic autumn communities, respectively. The presence of these cystacanths in different mesozooplankton communities throughout the study suggests that the recruitment of parasites may be affected by the oceanography.

Impact of acanthocephalan parasites on aggregation behavior of amphipods (Gammarus pseudolimnaeus)

Acanthocephalan parasites can manipulate the behavior of their amphipod intermediate hosts in ways that increase the amphipod's risk of being eaten by a predator that serves as the final host for the parasite. Some asocial amphipod species have been shown to increase the likelihood of aggregation in response to chemical cues associated with predators. If such aggregation has anti-predation benefits, it might be subject to manipulation by parasites. We tested this hypothesis by comparing the preference of parasitized and unparasitized amphipods (Gammarus pseudolimnaeus) for associating with a group of unparasitized conspecifics, both in the presence and absence of chemical cues from predatory brook sticklebacks (Culaea inconstans). Amphipods with encysted parasites (Corynosoma sp.) avoided aggregating, whereas unparasitized amphipods preferred to aggregate. We also found that the risk of predation by sticklebacks faced by an individual amphipod was significantly lower when the amphipod was in a group compared to when it was alone. This suggests that the aggregation response of unparasitized amphipods is an adaptive response to escape predation. This study provides evidence for a novel parasitic manipulation of intermediate host behavior that is likely to increase transmission to the definitive host.

Polymorphus minutus affects antitoxic responses of Gammarus roeseli exposed to cadmium

The acanthocephalan parasite Polymorphus minutus is a manipulator of its intermediate host Gammarus roeseli, which favours its transmission to the final host, a water bird. In contaminated environments, G. roeseli have to cope with two stresses, i.e. P. minutus infection and pollutants. As P. minutus survival relies on its host's survival, we investigated the influence of P. minutus on the antitoxic defence capacities and the energy reserves of G. roeseli females after cadmium exposure. In parallel, malondialdehyde, a toxic effect biomarker, was measured in G. roeseli females and in P. minutus. The results revealed that infected females displayed higher cell damage than uninfected ones, despite an apparent increase in reduced glutathione and metallothionein production. In fact, the increase of these antitoxic systems could be counterbalanced by carotenoid intake by the parasite, so that the overall defence system seemed less efficient in infected females than in uninfected ones. In addition, we demonstrated that cadmium induced cell damage in P. minutus, probably linked with cadmium accumulation in the parasite. Altogether, we observed a paradoxical pattern of responses suggesting that P. minutus increases cadmium toxicity in G. roeseli females although (i) it tends to increase several host antitoxic defence capacities and (ii) it bears part of the pollutant, as reflected by cell damage in the parasite.

High serotonin levels due to the presence of the acanthocephalan Hexaglandula corynosoma could promote changes in behavior of the fiddler crab Uca spinicarpa

Between February and June 2010, 113 fiddler crabs Uca spinicarpa were collected from the Chuburna lagoon system on the northern coast of the Yucatan Peninsula, México. Of the 68 crabs gathered outside their burrows, 13 were infected with 25 cystacanths of Hexaglandula corynosoma (intensity of infection from 1 to 5) and the remaining 55 crabs were uninfected. The other 45 crabs were found inside their burrows and only one was found infected with 1 cystacanth of H. corynosoma. Serotonin (5-HT) levels were higher in the group of crabs infected with H. corynosoma in contrast to the group of uninfected crabs and the group of those infected with other parasites. A redundancy analysis corroborated a positive relationship between 5-HT and the intensity of infection with H. corynosoma. In contrast, dopamine levels remained similar among different groups of crabs.

Acanthocephalan parasites: help or burden in gammarid amphipods exposed to cadmium?

We investigated the influence of the acanthocephalan parasite Polymorphus minutus on the mortality of its intermediate host, Gammarus roeseli, exposed to cadmium, by the measure of LC(50-96h) values as well as the bioaccumulation of cadmium both in the host and in its parasite. LC(50) results revealed that infected G. roeseli males died less under cadmium stress than uninfected ones; while the converse has been observed in females. Cadmium resistance of infected males could be explained by a weaker bioconcentration factor (BCF) than in females. The lower BCF in infected individuals was closely related with an uptake of cadmium by P. minutus in its host. Nevertheless, although infected females had both weaker BCF and cadmium concentration in their body, the presence of P. minutus did not induce lower mortality than uninfected females. On the contrary, their sensitivity to cadmium was increased by the presence of P. minutus. We discuss the hypothesis that differences of mortality between uninfected and infected gammarids could be explained by a difference of cadmium bioconcentration in host, and by the cadmium bioaccumulation in the parasite. Indeed, results suggested that P. minutus could help G. roeseli to face with stress, what contributed to keep the host alive and favour the parasite transmission.

Population dynamics of a parasite Pallisentis in two species of fish Channa punctatus and Channa striatus

In an aquatic environment, there is a profound and inverse relationship between environment quality and disease status of fish. Parasites are one of the most serious limiting factors in aquaculture. Therefore, the present investigation has been undertaken to sort out the population dynamics of Pallisentis (Acanthocephala), in relation to host sex from freshwater fishes, Channa of Rohilkhand region. A total of 517 fishes (Channa punctatus, n = 198 and C. striatus, n = 319) were examined regularly from August 2006 to February 2010. Overall prevalence of Pallisentis in C. striatus was higher in females (67.78%) as compared to males (63.52%). In case of C. punctatus, overall prevalence of Pallisentis was higher in males (53.77%) as compared to females (52.17%) whereas, relative density was higher in females (61.41%) than in males (52.72%). Intensity (2-3 parasite/host, in both sexes), density (1.36 in males and 1.69 in females) and infection index (0.73 in males and 0.88 in females) were recorded.

Molecular phylogeny of the Acanthocephala (class Palaeacanthocephala) with a paraphyletic assemblage of the orders Polymorphida and Echinorhynchida

Acanthocephalans are attractive candidates as model organisms for studying the ecology and co-evolutionary history of parasitic life cycles in the marine ecosystem. Adding to earlier molecular analyses of this taxon, a total of 36 acanthocephalans belonging to the classes Archiacanthocephala (3 species), Eoacanthocephala (3 species), Palaeacanthocephala (29 species), Polyacanthocephala (1 species) and Rotifera as outgroup (3 species) were analyzed by using Bayesian Inference and Maximum Likelihood analyses of nuclear 18S rDNA sequence. This data set included three re-collected and six newly collected taxa, Bolbosoma vasculosum from Lepturacanthus savala, Filisoma rizalinum from Scatophagus argus, Rhadinorhynchus pristis from Gempylus serpens, R. lintoni from Selar crumenophthalmus, Serrasentis sagittifer from Johnius coitor, and Southwellina hispida from Epinephelus coioides, representing 5 new host and 3 new locality records. The resulting trees suggest a paraphyletic arrangement of the Echinorhynchida and Polymorphida inside the Palaeacanthocephala. This questions the placement of the genera Serrasentis and Gorgorhynchoides within the Echinorhynchida and not the Polymorphida, necessitating further insights into the systematic position of these taxa based on morphology.

[Convergence of the cyst in cysticercoids (Cestoda, Hymenolepidata) and the tegument in cystacanths (Acanthocephala)]

It was shown that despite fundamental differences in the organization of the tegument of cystacanths and the cyst wall of cysticeroids, they have a number of features similar in localization, morphology, terms of formation, and functional value. These include a powerful outer layer of glycocalyx on the surface of the tegument, filling of the distal department with dense substance, and the presence of complicated fibrillar systems. It is supposed that the nature of these particularities is convergent and is determined by the similarity of the life cycles of Hymenolepidata and Acanthocephala.

The response of intestinal mucous cells to the presence of enteric helminths: their distribution, histochemistry and fine structure

Histochemical and ultrastructural investigations were conducted on the mucous cells of the intestine of brown trout, Salmo trutta L., naturally infected with the cestode Cyathocephalus truncatus (Pallas, 1781) and the acanthocephalan Echinorhynchus truttae Shrank, 1788. A subpopulation of 45 S. trutta were examined of which 15 specimens harboured E. truttae, 15 of which were infected with C. truncatus and 15 fish, the control group, were uninfected. In histological sections, hyperplasia and hypertrophy of the mucous cells were evident at the site of parasite infection. Enhanced mucus secretion was also recorded in infected fish. The number of mucous cells close to the site of parasite attachment within the intestine was significantly higher than the number detected in uninfected individuals and in infected individuals at sites 1 cm or greater from the point of parasite attachment. There were no significant differences between the number of mucous cells found at the latter two sites. Alcian blue and periodic acid-Schiff's staining of representative histological sections revealed a significant increase in the number of mucous cells staining positively for acid glycoconjugates compared to the number of cells found in the intestines of uninfected S. trutta. In transmission electron microscopy sections, each mucous cell typically possessed an elongated, basally positioned nucleus. The cytoplasm was observed to possess numerous electron dense and lucent vesicles, in addition to well-developed rough endoplasmic reticulum, Golgi apparatus and a few round mitochondria.

Carotenoid-based colour of acanthocephalan cystacanths plays no role in host manipulation

Manipulation by parasites is a catchy concept that has been applied to a large range of phenotypic alterations brought about by parasites in their hosts. It has, for instance, been suggested that the carotenoid-based colour of acanthocephalan cystacanths is adaptive through increasing the conspicuousness of infected intermediate hosts and, hence, their vulnerability to appropriate final hosts such as fish predators. We revisited the evidence in favour of adaptive coloration of acanthocephalan parasites in relation to increased trophic transmission using the crustacean amphipod Gammarus pulex and two species of acanthocephalans, Pomphorhynchus laevis and Polymorphus minutus. Both species show carotenoid-based colorations, but rely, respectively, on freshwater fish and aquatic bird species as final hosts. In addition, the two parasites differ in the type of behavioural alteration brought to their common intermediate host. Pomphorhynchus laevis reverses negative phototaxis in G. pulex, whereas P. minutus reverses positive geotaxis. In aquaria, trout showed selective predation for P. laevis-infected gammarids, whereas P. minutus-infected ones did not differ from uninfected controls in their vulnerability to predation. We tested for an effect of parasite coloration on increased trophic transmission by painting a yellow-orange spot on the cuticle of uninfected gammarids and by masking the yellow-orange spot of infected individuals with inconspicuous brown paint. To enhance realism, match of colour between painted mimics and true parasite was carefully checked using a spectrometer. We found no evidence for a role of parasite coloration in the increased vulnerability of gammarids to predation by trout. Painted mimics did not differ from control uninfected gammarids in their vulnerability to predation by trout. In addition, covering the place through which the parasite was visible did not reduce the vulnerability of infected gammarids to predation by trout. We discuss alternative evolutionary explanations for the origin and maintenance of carotenoid-based colorations in acanthocephalan parasites.

Inflammatory response to Dentitruncus truttae (Acanthocephala) in the intestine of brown trout

Brown trout, Salmo trutta L., were infected with the acanthocephalan Dentitruncus truttae with the most affected areas being the anterior (near the pyloric caeca) and middle intestine. The parasite attached with a proboscis which usually penetrated the mucosa, lamina propria, stratum compactum, stratum granulosum and, sometimes, the muscularis layer. Around the parasite's body was an area of inflammatory tissue. At the point of attachment the lamina propria was thickened and the stratum compactum, stratum granulosum and muscularis layer were disrupted by proboscis penetration. Rodlet cells were more numerous in infected fish (P<0.01), and were found in the epithelial layer away from the worm. Infected intestines had larger numbers of mast cells (P<0.01), often in close proximity to, and inside, the blood capillaries and associated with fibroblasts of the muscularis layer and the stratum granulosum. Their migration toward the site of infection was suggested. Intense degranulation of mast cells was encountered in all intestinal layers especially near the parasite's body. Immunohistochemical tests were conducted on sections of intestinal tissue of uninfected and infected fish revealing the presence of met-enkephalin and serotonin (5-HT) in immuno-related cells of the intestine wall. Infected trout had larger numbers of elements positive to met-enkephalin and serotonin antisera. These data provided evidence for the role of the immune system of brown trout in the modulation of the inflammatory response to D. truttae. Results are discussed with respect to host immune response to an intestinal helminth.

[Vertical distribution of acanthocephalans of the order Echinorhynchida in Lake Baikal]

Vertical distribution of acanthocephalans of the order Echinorhynchida is studied in Lake Baikal. Four species and subspecies from cottid fishes (Perciformes: Cottoidei) were examined, namely Pseudoechinorhynchus borealis (Linstow, 1901), Metechinorhynchus salmonis salmonis (Muller, 1780), M.s. baicalensis Bogolepova, 1957, M. truttae (Schrank, 1788). In the littoral (0-5 m) and sublittoral (5-100 m) areas all these species and subspecies were occurred, white in the profundal (100-300 m) and abyssal (900-1600 m) areas only Metechinorhynchus salmonis baisalensis has been found.

[Animal corynosomosis is a potential human helminthiasis in the Republic of Belarus]

In the Republic of Belarus, one representative of the genus Corynosoma - C. strumosum (Rudolphi, 1802) that is a causative agent of corynosomosis and that is of medical value is parasitic on animals. In Belarus, this proboscis worm has been encountered only in European and American minks. The author of the paper found this helminth in 2 of the 50 examined American minks in Byelorussian Polesye in 1980-2001. In this region, there were no C. strumosum larvae in fishes (1394 fishes of 21 species were studied). It is noted that the American mink plays a dominant role in the circulation of invasion and the attention of medical workers ofBelarus is drawn to the existing risk of human infection with the pathogen of Corynosomosis.

Helminth parasites of stellate sturgeon Acipenser stellatus Pallas, 1771 and Persian sturgeon Acipenser persicus Borodin, 1897 (Pisces: Acipenseridae) from the South-East Caspian Sea

A total of 182 specimens of two sturgeon species, stellate sturgeon Acipenser stellatus (N=112) and Persian sturgeon Acipenser persicus (N=70), from three coastal stations in the South-East Caspian Sea were examined for endohelminth parasites. Four helminth species were recorded: Cucullanus sphaerocephala (Nematoda: Cucullanidae) and Skrjabinopsolus semiarmatus (Digenea: Acanthocolpidae), found in both host species, and Leptorhynchoides plagicephalus (Acanthocephala: Rhadinorhynchidae) and Amphilina foliacea (Cestodaria: Amphilinidae), found only in A. stellatus. The most abundant parasites were C. sphaerocephala and S. semiarmatus in A. persicus and A. stellatus, respectively. Canonical discriminant analysis was applied for separating host species using parasite numbers data, Brillouin index of diversity, and species richness. By this means, 83% of the hosts were assigned to their correct a priori groups. The different feeding habits and habitat preferences of the two hosts are probably the major factors accounting for the difference in their parasite burdens.

[Corynosoma hannae Zdzitowiecki, 1984--a parasite of sea leopard from the Pacific sector of Antarctic]

Specimens of the acanthocephalan Corynosoma hannae Zdzitowiecki, 1984 from the Pacific (Balleni islands) and Atlantic (South Shetland) sectors of Antarctic are compared with those from the Pacific sector of Subantarctic (Auckland and Campbell islands). Probably New Zealand sea lion Phocarctos hookeri (Gray, 1844) is the secondary definitive host for Corynosoma hannae. Description and figures of the specimens examined are provided.

Differential influence of Pomphorhynchus laevis (Acanthocephala) on brain serotonergic activity in two congeneric host species

The physiological mechanisms by which parasites with complex life cycles manipulate the behaviour of their intermediate hosts are still poorly understood. In Burgundy, eastern France, the acanthocephalan parasite Pomphorhynchus laevis inverses reaction to light in its amphipod host Gammarus pulex, but not in Gammarus roeseli, a recent invasive species. Here, we show that this difference in manipulation actually reflects a difference in the ability of the parasite to alter brain serotonergic (5-HT) activity of the two host species. Injection of 5-HT in uninfected individuals of both host species was sufficient to inverse reaction to light. However, a difference in brain 5-HT immunocytochemical staining levels between infected and uninfected individuals was observed only in G. pulex. Local adaptation of the parasite to the local host species might explain its inability to manipulate the behaviour and nervous system of the invasive species.

ISOPOD (ASELLUS AQUATICUS) SIZE AND ACANTHOCEPHALAN (ACANTHOCEPHALUS LUCII) INFECTIONS

We examined the effect of isopod size and age on the success of an acanthocephalan infection and on the effects of that infection on the growth and survival of the isopods. Groups of isopods (Asellus aquaticus) belonging to 4 size classes (juveniles, maturing adults, young adults, and older adults) were exposed to infective acanthors of Acanthocephalus lucii. At the end of the experiment, survival of the isopods, lengths of male and female isopods, and numbers of different developmental stages of A. lucii larvae in infected isopods were assessed. Acanthocephalus lucii prevalence was significantly lower in juvenile isopods than in adults. Intensity of infection increased with the size of isopods at exposure, and cystacanth intensity correlated positively with isopod size at the end of the experiment. Exposed juveniles and maturing adults survived significantly better than unexposed individuals, but the opposite was true of the 2 largest size classes. At the end of experiment, exposed isopods, and, especially, cystacanth-infected isopods, were significantly larger than unexposed isopods in every size class. We suggest that isopod size not only affects the success of A. lucii infection but also affects the ability of A. lucii to affect the survival (and perhaps the growth) of the isopod hosts.

PARASITE-RELATED PAIRING SUCCESS IN AN INTERMEDIATE HOST, CAECIDOTEA INTERMEDIUS (ISOPODA): EFFECTS OF MALE BEHAVIOR AND REPRODUCTIVE PHYSIOLOGY

The acanthocephalan parasite Acanthocephalus dirus develops from the egg to the cystacanth stage inside the freshwater isopod Caecidotea intermedius. We have shown previously that cystacanth-infected male C. intermedius are less likely to initiate mating attempts with females than uninfected males in competitive situations. Here, we used a field-based experiment to examine whether cystacanth-infected males were also less likely to initiate mating attempts with females in noncompetitive situations. We found that infected males were less responsive to females than uninfected males, and we propose that the cystacanth-related change in male mating behavior is mediated by a change in the mating response of males to females rather than male-male competition. We then examined whether cystacanth-related changes in reproductive function, i.e., sperm content and fertilization ability, could explain this variation in male mating behavior. We found that cystacanth-infected males contained both developing and mature sperm and fertilized as many eggs as uninfected males. Thus, we propose that changes in reproductive function are unlikely to explain cystacanth-related variation in male mating behavior in C. intermedius.

Increased susceptibility to predation and altered anti-predator behaviour in an acanthocephalan-infected amphipod

According to the 'parasitic manipulation hypothesis', phenotypic changes induced by parasites in their intermediate hosts are effective means of increasing trophic transmission to final hosts. One obvious prediction, although seldom tested, is that increased vulnerability of infected prey to an appropriate predator should be achieved by the parasite altering the anti-predator behaviour of its intermediate host. In this study, we tested this prediction using the fish acanthocephalan Pomphorhynchus tereticollis and the freshwater amphipod Gammarus pulex. Firstly, we estimated the relative vulnerability of infected and uninfected gammarids to predation by the bullhead Cottus gobio in the field. Second, we investigated under experimental conditions how two common anti-predator behaviours of aquatic invertebrates, refuge use and short-distance reaction to predator chemical cues, were affected by infection status. We found that the prevalence of infection in the field was 10 times higher among gammarids collected from the stomach contents of bullheads compared with free-ranging individuals collected in the same river. In a microcosm uninfected gammarids, but not infected ones, increased the use of refuge in the presence of a bullhead. Finally, a behavioural experiment using an Y-maze olfactometer showed opposite reactions to predator odour. Whereas uninfected gammarids were significantly repulsed by the chemical cues originating from bullheads, infected ones were significantly attracted to the odour of the predator. Taken together, our results suggest that the alteration of anti-predator behaviour in infected G. pulex might enhance predation by bullheads in the field. Reversing anti-predator behaviour might thus be an efficient device by which parasites with complex life-cycles increase their trophic transmission to final hosts. Further studies should pay more attention to both the increased vulnerability of infected prey to an appropriate predator in the field and the influence of parasitic infection on the anti-predator behaviour of intermediate hosts.

Altered host behaviour and brain serotonergic activity caused by acanthocephalans: evidence for specificity

Manipulative parasites can alter the phenotype of intermediate hosts in various ways. However, it is unclear whether such changes are just by-products of infection or adaptive and enhance transmission to the final host. Here, we show that the alteration of serotonergic activity is functionally linked to the alteration of specific behaviour in the amphipod Gammarus pulex infected with acanthocephalan parasites. Pomphorhynchus laevis and, to a lesser extent, Pomphorhynchus tereticollis altered phototactism, but not geotactism, in G. pulex, whereas the reverse was true for Polymorphus minutus. Serotonin (5-hydroxytryptamine, 5-HT) injected to uninfected G. pulex mimicked the altered phototactism, but had no effect on geotactism. Photophilic G. pulex infected with P. laevis or P. tereticollis showed a 40% increase in brain 5-HT immunoreactivity compared to photophobic, uninfected individuals. In contrast, brain 5-HT immunoreactivity did not differ between P. minutus-infected and uninfected G. pulex. Finally, brain 5-HT immunoreactivity differed significantly among P. tereticollis-infected individuals in accordance with their degree of manipulation. Our results demonstrate that altered 5-HT activity is not the mere consequence of infection by acanthocephalans but is specifically linked to the disruption of host photophobic behaviour, whereas the alteration of other behaviours such as geotactism may rely on distinct physiological routes.

Utilization of brown troutSalmo truttabyAcanthocephalus clavulain an Irish lake: is this evidence of a host shift?

The population biology of the fish acanthocephalanAcanthocephalus clavulawas described from 161 wild brown trout,Salmo truttasampled over a two-year period in Clogher Lake in the west of Ireland. Overall prevalence of the parasite was 86% and the mean abundance was 53 worms per fish. Despite the presence of large numbers of worms in the trout very few females (2%) attained full reproductive maturity. This suggests that trout is an accidental host. A sample of yellow eels,Anguilla anguillawas examined at a different time from the same lake. The prevalence ofA. clavulawas 97% and the average abundance was 8 worms per fish. In contrast to the situation in trout, the proportion of female worms attaining full reproductive maturity was 61% fulfilling the expected characteristic of a preferred definitive host. The possible explanations for the very high abundance ofA. clavulain trout are discussed and include the influence of fluctuations in host populations, host diet and the absence of a potential competitor.

Seasonality of recruitment and reproduction of Acanthocephalus tumescens (Acanthocephala) in fishes from Lake Moreno (Patagonia, Argentina)

The seasonality of recruitment and reproduction of Acanthocephalus tumescens at the component population level was investigated in Lake Moreno (Patagonia, Argentina). Seasonal samples of the principal fish host species were taken between spring 1999 and spring 2000. Prevalence, mean intensity, coefficient of dispersion, sex ratio, proportion of maturity stages of females, and percentages of the 2 sources of infection in the stomach of fishes were calculated. Overall prevalence, mean intensity, and coefficient of dispersion showed the same pattern of seasonal changes. The seasonal feeding patterns of fishes affect the occurrence of A. tumescens, producing 1 peak in spring and the other peak in autumn. The lower temperature in winter delay reproductive processes after the autumn period of recruitment.

Do distantly related parasites rely on the same proximate factors to alter the behaviour of their hosts?

Phylogenetically unrelated parasites often increase the chances of their transmission by inducing similar phenotypic changes in their hosts. However, it is not known whether these convergent strategies rely on the same biochemical precursors. In this paper, we explored such aspects by studying two gammarid species (Gammarus insensibilis and Gammarus pulex; Crustacea: Amphipoda: Gammaridae) serving as intermediate hosts in the life cycle of two distantly related parasites: the trematode, Microphallus papillorobustus and the acanthocephalan, Polymorphus minutus. Both these parasite species are known to manipulate the behaviour of their amphipod hosts, bringing them towards the water surface, where they are preferentially eaten by aquatic birds (definitive hosts). By studying and comparing the brains of infected G. insensibilis and G. pulex with proteomics tools, we have elucidated some of the proximate causes involved in the parasite-induced alterations of host behaviour for each system. Protein identifications suggest that altered physiological compartments in hosts can be similar (e.g. immunoneural connexions) or different (e.g. vision process), and hence specific to the host-parasite association considered. Moreover, proteins required to alter the same physiological compartment can be specific or conversely common in both systems, illustrating in the latter case a molecular convergence in the proximate mechanisms of manipulation.

Infection pattern of two sympatric acanthocephalan species in the amphipod Hyalella patagonica (Amphipoda: Hyalellidae) from Lake Mascardi (Patagonia, Argentina)

The aim of the present study was to describe the infection pattern of the acanthocephalans Acanthocephalus tumescens and Corynosoma sp. co-occurring in the intermediate host the amphipod Hyalella patagonica. Samples were collected monthly from June 2002 to May 2004 from Lake Mascardi. Amphipods were measured and classified by developmental stages. Single and double infections of larval acanthocephalans were recorded and prevalence and mean intensity were calculated. An annual life cycle of H. patagonica could be inferred with recruitment of juveniles from spring to autumn. Males and females were found all year round but females were significantly more abundant. Single infections were mainly found in smaller juvenile amphipods during winter for A. tumescens and in intermediate and large male amphipods during spring and summer for Corynosoma sp. Double infections showed low values and were mainly found in intermediate sized amphipods during spring. A segregation of the infection by season, size and developmental stages of the host was recorded and would tend to avoid competition considering these two acanthocephalan species have different definitive hosts: fishes for A. tumescens and aquatic birds for Corynosoma sp.