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Acanthocephalans are parasites with complex lifecycles that are important components of aquatic systems and are often model species for parasite-mediated host manipulation. Genetic characterization has recently resurrectedPomphorhynchus tereticollisas a distinct species fromPomphorhynchus laevis, with potential implications for fisheries management and host manipulation research. Morphological and molecular examinations of parasites from 7 English rivers across 9 fish species revealed thatP. tereticolliswas the onlyPomphorhynchusparasite present in Britain, rather thanP. laevisas previously recorded. Molecular analyses included two non-overlapping regions of the mitochondrial gene – cytochrome oxidase and generated 62 sequences for the shorter fragment (295 bp) and 74 for the larger fragment (583 bp). These were combined with 61 and 13 sequences respectively, from Genbank. A phylogenetic analysis using the two genetic regions and all the DNA sequences available forP. tereticollisidentified two distinct genetic lineages in Britain. One lineage, possibly associated with cold water tolerant fish, potentially spread to the northern parts of Britain from the Baltic regionviaa northern route across the estuarine area of what is now the North Sea during the last Glaciation. The other lineage, associated with temperate freshwater fish, may have arrived laterviathe Rhine/Thames fluvial connection during the last glaciation or early Holocene when sea levels were low. These results raise important questions on this generalist parasite and its variously environmentally adapted hosts, and especially in relation to the consequences for parasite vicariance.

Adult specimens of Pomphorhynchus fuhaiensis were identified from common carp (Cyprinus carpio L.) in Ulungur Lake of northwest China, and acanthors, acanthellae, cystacanths dissected from Gammarus lacustris in a small tributary of Ulungur River for the first time. The acanthocephalans were also found in crucian carp (Carassius carassius L.), tench (Tinca tinca L.), oriental bream (Abramis brama orientalis Berg), and ide (Leuciscus idus L.) in the lake. This species is distinguished from other species in Pomphorhynchus by its large, spherical bulb and very long neck as well as by a cylindrical proboscis armed with 15-17 longitudinal rows of 9-12 hooks each. The anterior proboscis hooks are almost uniform in size and shape, the sixth hook in a short row and the seventh hook in long row decrease abruptly in size posteriorly with the last end hook being a little larger than the prebasal hook, and in a ring; posterior proboscis hooks much more widely spaced. Furthermore, the lemnisci are claviform. The mean neck:trunk ratio is about 0.5, which is larger than most other species in Pomphorhynchus. Females are larger than males. In males, the testes are in one-third to one-half of the trunk, equal, ovoid-spheroid, usually contiguous, and small relative to the body size, and there are 6 ovoid cement glands. Pomphorhynchus fuhaiensis is similar to Pomphorhynchus laevis but can be distinguished by the number of longitudinal rows of hooks. Pomphorhynchus laevis is armed with 18-20 longitudinal rows of 11-13 hooks, P. fuhaiensis is armed with 15-17 longitudinal rows of 9-12 hooks.

Summary Species diversity and composition of the parasite communities of barbel (Barbus barbus) at the infracommunity and component community levels were studied in the Lower Danube River, Bulgaria. During the two-year investigations, five parasite species have been found in 92 host fish: Bathybothrium rectangulum (Cestoda), Acanthocephalus anguillae and Pomphorhynchus laevis (Acanthocephala) and larval stages of Contracaecum sp. and Raphidascaris acus (Nematoda). Bathybothrium rectangulum and R. acus found in barbel represented new host records in Bulgaria. Parasite communities of barbel were species-poor and highly unbalanced. Pomphorhynchus laevis represented the dominant (core) species (prevalence 98.9 %), the second most frequent component parasite was Contracaecum sp. (P = 14.1 %) and remaining three species occurred only accidentally in barbels. Differences in species richness, prevalence, intensity of infection and ecological indices between individual seasons (spring, summer, autumn) were statistically significant, but considerably affected by unequal species structure of communities with highly prevailing P. laevis. Low parasite species diversity of barbel and low values of most ecological indices, when compared with previous studies in this area (or other Bulgarian parts of the River Danube) might indicate that environmental conditions are impaired and thus, not favourable for the development of barbel parasites (primarily to their intermediate host survival) in the Lower Danube River of Bulgaria.

Parasite distribution among hosts is a fundamental aspect of host–parasite interactions. Aggregated parasite distributions within and across host species are commonly reported and potentially influenced by many factors, whether host or parasite specific, or related to host–parasite encounter and compatibility. Yet, the respective role of each in observed parasite distributions are often unclear. Here, we documented the distribution of the acanthocephalan parasitePomphorhynchus laevis sensu lato(s.l.) in two replicate fish host populations. Aggregated distributions were observed in both populations, within and across fish host species. We found a positive abundance–prevalence relationship across fish species, suggesting that resource availability (fish host biomass density) was the main driver ofP. laevis s.l.distribution. This was supported by further positive associations between mean parasite load and fish biomass density. We found little evidence for intensity-dependent regulation within host (i.e. intra-host competition among co-infecting parasites). Furthermore,P. laevis s.l.infection had no detectable effect on fish condition indices, except on the body condition of female barbel (Barbus barbus). Therefore,P. laevis s.l.tended to accumulate with size/age within fish species, and with fish biomass density among fish species, with apparently negligible limitations due to intra-host intensity-dependent regulation of parasite, or to parasite-induced morbidity in fish. The relative availability of final hosts for trophic transmission thus appears to be the main driver ofP. laevis s.l.distribution among fish.

We suggest helminthological investigations of cod as a supplement to traditional biological and hydrographical methods for elucidation of ecological changes in the Baltic Sea. It is under discussion if oxygen deficit or seal abundance should explain the present critical situation of Baltic cod. A comparative investigation of endoparasitic helminths in Baltic cod (Gadus morhua), captured in the same marine habitat with an interval of 35 years (1983/2018) recorded 11 species of helminths comprising trematodes (Hemiurus luehei, Podocotyle atomon, Lepidapedon elongatum), nematodes (Contracaecum osculatum, Hysterothylacium aduncum, Capillaria gracilis, Cucullanus cirratus), cestodes (Bothriocephalus sp.) and acanthocephalans (Echinorhynchus gadi, Pomphorhynchus laevis, Corynosoma semerme). Significant prevalence and intensity increases were recorded for third-stage larvae of the nematode C. osculatum (liver location) and larvae of C. semerme (encapsulated in viscera). Both parasite species use grey seal as their final host, indicating the recent expansion of the Baltic seal population. A lower E. gadi intensity and an increased prevalence of L. elongatum of small cod (31–40 cm body length) suggest a lowered intake of amphipods (intermediate host) and elevated ingestion of polychaetes, respectively, but no significant changes were seen for other helminths.

13 pages; International audience; Parasitism is an important process in ecosystems, but has been largely neglected in ecosystem research. However, parasites are involved in most trophic links in food webs with, in turn, a major role in community structure and ecosystem processes. Several studies have shown that higher nutrient availability in ecosystems tends to increase the prevalence of parasites. Yet, most of these studies focused on resource availability, whereas studies investigating resource quality remain scarce. In this study, we tested the impact of the quality of host food resources on infection by parasites, as well as on the consequences for the host. Three resources were used to individually feed Gammarus pulex (Crustacea: Amphipoda) experimentally infected or not infected with the acanthocephalan species Pomphorhynchus laevis: microbially conditioned leaf litter without phosphorus input (standard resource); microbially conditioned leaf litter enriched in phosphorus; and microbially conditioned leaf litter without phosphorus input but complemented with additional inputs of benthic diatoms rich in both phosphorus and eicosapentaenoic acid. During the 110 day experiment, infection rate, parasite load, host survival, and parasite-mediated behavioral traits implicated in trophic transmission were measured (refuge use, geotaxis and locomotor activity). The resources of higher quality, regardless of the infection status, reduced gammarid mortality and increased gammarid growth. In addition, higher quality resources increased the proportion of infected gammarids, and led to more cases of multi-infections. While slightly modifying the geotaxis behavior of uninfected gammarids, resource quality did not modulate the impact of parasites on host behavior. Finally, for most parameters, consumption of algal resources had a greater impact than did phosphorus-enriched leaf litter. Therefore, manipulation of resource quality significantly affected host-parasite relationships, which stressed the need for future research to investigate in natura the relationships between resource availability, resource quality and parasite prevalence.

Interspecific interactions between parasites sharing the same host are often antagonistic; the presence of one species decreases the number of individuals or negatively affects both the distribution and reproduction of the other species. Antagonistic interactions between co-infecting parasites may translate into direct competition or interactive segregation, but elements of both may be present. Potential interactions between two acanthocephalan species, Pomphorhynchus laevis and Acanthocephalus anguillae, were studied in the field in two of their natural fish definitive hosts. There was no evidence for competitive exclusion between P. laevis and A. anguillae. However, a negative interaction was found for the first time in the field between these two species. Based on the analysis of parasite abundance and total biomass using a static regression approach, I found that the abundance and total biomass of parasites was also limited by host characteristics. These results are consistent with previous laboratory studies on competition between P. laevis and A. anguillae.

Parasites with complex life-cycles and trophic transmission are expected to show low specificity towards final hosts. However, testing this hypothesis may be hampered by low taxonomic resolution, particularly in helminths. We investigated this issue using two intestinal fish parasites with similar life-cycles and occurring in sympatry, Pomphorhynchus laevis and Pomphorhynchus tereticollis (Acanthocephala). We used species-specific ITS1 length polymorphism to discriminate parasite species from 910 adult acanthocephalans collected in 174 individual hosts from 12 fish species. Both P. laevis and P. tereticollis exhibited restricted host range within the community of available fish host species, and transmission bias compared to their relative abundance in intermediate hosts. The two parasites also exhibited low niche overlap, primarily due to their contrasting use of bentho-pelagic (P. laevis) and benthic (P. tereticollis) fish. Furthermore, parasite prevalence in intermediate hosts appeared to increase with taxonomic specificity in definitive host use. Comparison of P. laevis and P. tereticollis adult size in the two main definitive hosts, barbel and chub, suggested lower compatibility towards the fish species with the lowest parasite abundance, in particular in P. laevis. The determinants of low niche overlap between these two sympatric acanthocephalan species, and the contribution of definitive host range diversity to parasite transmission success, are discussed. Keywords: Compatibility, Complex life-cycle, Freshwater, Host range, Index, Reproduction, Specificity

Species of the genus Pomphorhynchus Monticelli, 1905 (Acanthocephala: Pomphorhynchidae) are obligate endoparasites infesting mostly freshwater fish. Morphological identification is challenging due to high intraspecific variations. The use of molecular analyses enabled new insights into the diversity and revealed high cryptic presence and unknown distribution patterns for various European species. In Austria only one species, Pomphorhynchus laevis (Müller, 1776), has been reported so far. We conduct an integrative analysis of Pomphorhynchus in Austria with a combination of morphological and molecular methods. Our results revealed the presence of three species of Pomphorhynchus in Austrian waters: Pomphorhynchus laevis, Pomphorhynchus tereticollis (Rudolphi, 1809) and Pomphorhynchus bosniacus Kiskároly and Čanković, 1967. While P. bosniacus was the predominant species in the Danube, P. laevis was recorded exclusively in Styria. Pomphorhynchus tereticollis occurred mainly in rivers of Styria except for one individual found in the Danube. We document the first occurrence of P. bosniacus and P. tereticollis in Austria. We found a high intraspecific haplotype variation in P. bosniacus suggesting that the species has a longer history in Central and Western Europe. It was previously misidentified as P. laevis, which is also true for P. tereticollis. A large number of hosts examined were infected with only juvenile and cystacanth stages suggesting paratenic infections. Our study highlights the importance of using an integrative taxonomic approach in the identification of species of Pomphorhynchus. Keywords: Acanthocephala, Pomphorhynchus spp., Austria, Fish, Autofluorescence imaging, Integrative taxonomy, 3-D reconstruction

The round goby, Neogobius melanostomus, is a Ponto-Caspian fish considered as an invasive species in a wide range of aquatic ecosystems. To understand the role that parasites may play in its successful invasion across Western Europe, we investigated the parasitic diversity of the round goby along its invasion corridor, from the Danube to the Upper Rhine rivers, using data from literature and a molecular barcoding approach, respectively. Among 1666 parasites extracted from 179 gobies of the Upper Rhine, all of the 248 parasites barcoded on the c oxidase subunit I gene were identified as Pomphorhynchus laevis. This lack of macroparasite diversity was interpreted as a loss of parasites along its invasion corridor without spillback compensation. The genetic diversity of P. laevis was represented by 33 haplotypes corresponding to a haplotype diversity of 0·65 ± 0·032, but a weak nucleotide diversity of 0·0018 ± 0·00015. Eight of these haplotypes were found in 88·4% of the 248 parasites. These haplotypes belong to a single lineage so far restricted to the Danube, Vistula and Volga rivers (Eastern Europe). This result underlines the exotic status of this Ponto-Caspian lineage in the Upper Rhine, putatively disseminated by the round goby along its invasion corridor.

SUMMARYPredicting how elevated temperatures from climate change alter host–parasite interactions requires understandings of how warming affects host susceptibility and parasite virulence. Here, the effect of elevated water temperature and parasite exposure level was tested on parasite prevalence, abundance and burden, and on fish growth, using Pomphorhynchus laevis and its fish host Squalius cephalus. At 60 days post-exposure, prevalence was higher at the elevated temperature (22 °C) than ambient temperature (18 °C), with infections achieved at considerably lower levels of exposure. Whilst parasite number was significantly higher in infected fish at 22 °C, both mean parasite weight and parasite burden was significantly higher at 18 °C. There were, however, no significant relationships between fish growth rate and temperature, parasite exposure, and the infection parameters. Thus, whilst elevated temperature significantly influenced parasite infection rates, it also impacted parasite development rates, suggesting warming could have complex implications for parasite dynamics and host resistance.

Pomphorhynchus tereticollis (Rudolphi, 1809) is here redescribed on the basis of Rudolphi’s material, deposited in the Museum für Naturkunde Berlin, and on acanthocephalans recently collected from the type host Platichthys flessus (L.) and the region embodying the type locality. Out of the paratypes of P. tereticollis, the lectotype and paralectotypes have been designated. Their morphology fits well with that of newly collected material of P. tereticollis dissected from the type fish host from the Baltic coast near Stralsund. The resurrection of P. tereticollis, previously considered a synonym of Pomphorhynchus laevis (Zoega in Müller, 1779), is supported by several morphological features distinguishing the two Pomphorhynchus species: 1. The basal parts of the proboscis hooks located on the posterior proboscis half possess proximal projections in P. tereticollis but not in P. laevis. This shape of the hook bases is clearly visible only in unfixed fresh worms; 2. The last hooks are situated at the anterior part of the bulbus or rarely at the posterior-most end of the proboscis in P. tereticollis, while they lie anterior to the end of the proboscis in P. laevis; 3. The proboscis hooks No. 5 or 6 are markedly stout (robust) and clearly distinct in comparison with the surrounding hooks in P. tereticollis, while less robust and more similar to the hooks in P. laevis. In addition, genetic divergence between P. tereticollis and P. laevis based on ITS1, ITS2 and COI sequencing supports the existence of two distinct species and reveals that some isolates previously identified as P. laevis were actually P. tereticollis. Previous and present morphological and genetic data show that both Pomphorhynchus species occur in freshwaters throughout Europe and may infect the same fish hosts, such as chub and barbel, and also several species of isopods (Gammaridae). This study also provides morphological evidence that Pomphorhynchus intermedius Engelbrecht, 1957 is a synonym of P. tereticollis, because the only discrimination character of the former species, the “existing but small proximal projections of basal parts of the proboscis hooks located on the posterior proboscis half” are present also in P. tereticollis.

SUMMARY Immunopathological and ultrastructural studies were conducted on the intestine of barbel Barbus barbus and sheatfish Silurus glanis that were naturally infected with the acanthocephalan Pomphorhynchus laevis. Enteric helminths often cause inflammation of the digestive tract, inducing the recruitment of different types of immune cells at the site of infection. The results of our study clearly demonstrated that mast cells (MC) were the dominant immune cells which occur at the site of inflammation in both hosts. MC were associated with fibroblasts and were found in close proximity to, and inside, the capillaries of the intestine, thus, migration of mast cells via the bloodstream was suggested. Significant degranulation of MC was present. Immunohistochemical staining revealed met-enkephalin and serotonin (5-HT) in intestinal MC of both uninfected and infected barbel and the absence of the antimicrobial peptides piscidin 3 and piscidin 4 in both species. Data are discussed with respect to host immune response to an intestinal helminth and compared with other host-parasite systems.

In this report, European common toads; Bufo bufo, European green toads Bufo viridis and marsh frogs Rana ridibunda were collected in Amasya, Çorum, and Tokat Provinces (Middle Black Sea Region of Turkey) 2005 and 2006 and examined for helminths. Two of 2 (100 %) Bufo bufo and 8 of 8 (100 %) Bufo viridis and 57 of 63 (90.5 %) Rana ridibunda were infected with 1 or more helminths. The helminths of B. bufo included Oswaldocruzia filiformis and Oxysomatium brevicaudatum. The helminth fauna of B. viridis comprised 5 species: 1 species of trematode (Pleurogenoides medians), 1 species of cestode (Nematotaenia dispar) and 3 species of nematodes, (Oswaldocruzia filiformis, Cosmocerca ornata, and Oxysomatium brevicaudatum), while the helminth fauna of Rana ridibunda comprised 9 species: 4 species of trematodes (Gorgodera cygnoides, Gorgoderina vitelliloba, Haematoloechus breviansa, and Opisthioglyphe ranae), 3 species of nematodes Oswaldocruzia filiformis, Cosmocerca ornata, and Oxysomatium brevicaudatum), and 2 species of acanthocephalans (Pomphorhynchus laevis and Acanthocephalus ranae). Oswaldocruzia filiformis, Cosmocerca ornata, and Oxysomatium brevicaudatum were collected from all three host species. In addition, Pleurogenoides medians represents a new host record for Bufo viridis in Turkey.

Three Eurasian otters (Lutra lutra) originating from Pazardzhik Region (South Bulgaria) were examined for helminth parasites. Three species of acanthocephalans were recorded: Pomphorhynchus laevis, Acanthocephalus anguillae and A. ranae. These species are not specific parasites of otters, the former two occurring in various freshwater fishes and the latter being a parasite of anurans. A review of acanthocephalan species recorded from L. lutra is presented. The possible transmission routes by which otters become infested with acanthocephalans are considered to be either paratenic transfer of encysted extra-intestinal juveniles in paratenic hosts or postcyclic transmission of mature intestinal worms in definitive hosts.

OA Förderung 2016 Background: A large number of studies demonstrated that acanthocephalans exhibit a high metal accumulation potential and thus can be used as sensitive accumulation indicators. However, similar to free-living bioindicators, a seasonal variation in metal concentrations in parasites might occur. Accordingly, the influence of seasonality has to be elucidated if parasites should be applied as sentinels. Methods: In order to assess a possible seasonal profile of element concentrations, the concentrations of As, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, V and Zn in the acanthocephalan Pomphorhynchus laevis and in its host barbel (Barbus barbus) were analysed in a seasonal manner (spring, summer and autumn) using inductively coupled plasma mass spectrometry (ICP-MS). Results: Five elements (As, Cd, Cu, Pb and Zn) were detected in significantly higher concentrations in the parasites compared to host muscle, intestine and liver. Their levels in P. laevis showed a clear seasonal pattern, while the concentrations in the fish tissues remained similar during the year. The highest concentrations in the parasites were found in autumn, followed by spring and summer. Evidence from the literature suggests that this profile coincides with the seasonality of acanthocephalan transmission, as their annual concentration profile reflected the mean individual weight pattern during the year. Parasite infrapopulations in autumn consisted mainly of young worms which are characterised by an accelerated metabolism and a higher surface to volume ratio resulting in higher element concentrations when compared to older worms which are assumed to slow down their metabolism and additionally excrete metals with their eggs. Conclusions: Based on the available data from the present study and literature, a model is suggested, which visualises the accumulation kinetic of several elements under natural conditions. According to the element accumulation data the lifespan of P. laevis in barbel was roughly estimated to range between six and eight months.

The parasitological studies were carried out on bream and perch from brackish water of Pomeranian Bay and the Szczecin Lagoon — a mouth of the Odra River. Bream and perch hosted 21 and 13 parasitic species, respectively. The species richness and diversity of parasites were much higher for bream and the abundance of parasites in bream was nearly four-fold higher than that in perch. Faunistic similarity of both parasite communities was low. The dominant group of parasites in both fish hosts was digeneans. Five species were specialists of bream, while only one species was a perch specialist. Five new host records have been reported in Poland for the following species: Myxobolus dispar, Hysterothylacium aduncum, Khawia sinensis, Echinorhynchus gadi and Pomphorhynchus laevis.

8 pages; International audience; Manipulative endoparasites with complex life cycles can alter their intermediate host immunity and behaviour in ways that increase survival probability within the host body cavity and enhance successful transmission to the definitive host. These parasitic manipulations are variable among and within parasite species and may result from co-evolutionary processes, in which the parasite is constrained for adaptation to the local intermediate host. Hence, arrival of a new host species in a local host population may promote local parasite maladaptation. This study tested the occurrence of local adaptation in two distantly located populations of the acanthocephalan parasite Pomphorhynchus laevis and its effect on the immunity and behaviour of its gammarid intermediate host Gammarus roeseli. This was done in France (an area for which G. roeseli is a recent invader) and Hungary (an area from which G. roeseli was believed to be native). As expected, we found no alteration in G. roeseli's immune defence and behaviour associated with infection by P. laevis in localities, where the gammarid is invasive. Unexpectedly, we found similar results in Hungarian populations, where the parasite was even more exposed to the host immune response. Whilst these results suggest maladaptation of the parasite to the gammarid in both countries, they also suggest that the gammarid host might be locally adapted to the parasite. Genetic analyses were performed on both the parasite and the host and the results suggest that the two subsets of populations we studied harbour rather isolated host-parasite systems, both probably deriving from a common ancestral population. We propose that G. roeseli is also of recent acquisition in Hungary, and that a recent co-evolutionary history between P. laevis and G. roeseli in association with a long generation time in the parasite has constrained parasite adaptations in Europe or even favoured host adaptation to the parasite.

The known metazoa parasite fauna of the invasive round goby Apollonia melanostoma (formerly Neogobius melanostomus) consists of 12 species. The core of the parasite fauna comprises two species: Cryptocotyle concavum and Diplostomum spathaceum; secondary species are absent; satellite species include Cercariae gen. sp. and Ergasilus sieboldi; rare species are Acanthocephalus lucii, Anguillicola crassus, Bothriocephalus sp., Dichelyne minutus, Hysterothylacium aduncum, Pomphorhynchus laevis, Piscicola geometra, and Tylodelphys clavata. Fifty percent of metazoa parasites that occurred in the invasive round goby in the Gulf of Gdańsk (an invasion that was first detected in 1990) are also typically found in the native Gulf of Gdańsk gobiids. The round goby hosts common fish parasite species: C. concavum and D. minutus, but none that are unique to the species and no Ponto-Caspian parasites. Notably, the parasite species of the invasive round goby in the Gulf of Gdańsk includes species that are atypical for this species in its native habitat. In its new habitat, the round goby variously serves the roles of definitive, second intermediate, and paratenic host for different parasite species. The fish species is involved in a parasitic system that includes fish-eating birds, fishes of different ecological groups (predatory, planktivorous, and benthivorous), and invertebrates.

The composition and diversity of the total and intestinal component endohelminth communities were determined in the cyprinid barbel from three study areas in two large river systems in Austria. Two sample sites in the Danube and one site in the River Drau are the only free flowing stretches of these rivers in Austria. Nine helminth species were identified, with the acanthocephalan Pomphorhynchus laevis being dominant in the Danube, with up to 100% prevalence. In the Drau, where the dominant species was the cestode Bathybothrium rectangulum, species diversity was higher than in the Danube.

Background. The hitherto published records of the parasite fauna of Baltic cod, Gadus morhua callarias cover commercially-caught adult fish. The aim of this study was to determine the composition of the parasite fauna of young Baltic cod, the relevant infection parameters and to relate those data to published records on the diet of cod. Materials and methods. This survey was carried out on 154 young cod, caught in May and June 2002 in the Gulf of Puck, the Baltic Sea, Poland. The fish were examined using standard methods applied in parasitology. Results. No external parasites were found. In the digestive tracts of 58 cod, 3 species of parasites belonging to 2 higher taxa (Nematoda and Acanthocephala) were found. The dominant parasite was Echinorhynchus gadi Zoega in Müller, 1776. The mean abundance ranged from 0.15 to 2.75. The prevalence ranged from 14.6%, in the smallest fish, to 66.7% in the larger ones. Only two acanthocephalan specimens of Pomphorhynchus laevis (Zoega in Müller, 1776) and five nematode larvae of Hysterothylacium aduncum (Rudolphi, 1802) were found. Conclusion. The parasite fauna of young Baltic cod is significantly sparser than in larger fish examined by other authors. It is suggested that the occurrence of the species found, can be related to the composition of diet available.

An analysis was undertaken of intestinal helminth communities in flounderPlatichthys flesusfrom two sites on the River Thames. A comparison was made between helminth community richness and diversity from these sites at the component and infracommunity levels. At the component community level, a richer and more diverse parasite community was found in flounder from the Tilbury location (marine influence) than that from the Lots Road location (freshwater influence). At the infracommunity level, more parasite species and parasite individuals per host were found at Lots Road and the percentage of similarity values were low at both locations. Helminth species with high prevalence values in the parasite communities of the flounder are the dominant species in any individual fish, harbouring multi-specific infections. The presence of more invertebrate species, which are intermediate hosts in the helminth life cycle in the Thames, fish vagility and the high prevalence and abundance values ofPomphorhynchus laevisin the flounder, may explain the differences between the two locations.

Pomphorhynchus laevis is believed on ecological evidence to exist as three strains in the British Isles. However, the strains have never been shown to be capable of being distinguished using morphological characters. A morphological comparison was made between a sample of P. laevis from Salmo trutta in L. Feeagh in the west of Ireland and a sample from Leuciscus cephalus in R. Culm in the south of England. The length and width of the trunk, neck, bulb, proboscis and hooks were measured. The number of hooks per row, the number of rows and the positions of the stoutest and longest hooks were also recorded. A Principal Components Analysis based on the morphological measurements confirmed the separation of the two populations and showed that two characters successfully identified the populations: the position of the stoutest hook and the ratio of numbers of anterior to posterior hooks.

Studies on parasite species with a wide geographic and ecological range may be confounded by still equivocal taxonomic identification. Here, we investigated genetic polymorphism and behavioural changes induced in a common intermediate host, in two different forms of Pomphorhynchus laevis based on the morphology of the larval infective stage (cystacanth). A 'smooth type' (S) and a 'wrinkled type' (W) of cystacanth were distinguished based on their surface and shape. We analysed sequence divergence at both nuclear (ribosomal gene 18S rDNA, and ribosomal internal transcribed spacers, ITS1/ITS2) and mitochondrial (cytochrome c oxidase subunit 1) genes of P. laevis cystacanths and adults at various geographical scales. A high level of sequence divergence at ITS1, ITS2 and cytochrome c oxidase subunit 1 (11, 8 and 20%, respectively) was found between these two forms. The divergence pattern consistently discriminated two groups independently of geographic origin or host, and was congruent with larval morphology. The two forms also strongly differed in the intensity of behavioural change induced in their common intermediate host, Gammarus pulex, with the S-type parasite inducing a positive phototactism, whereas W-type infected gammarids were as photophylic as uninfected ones. Overall, our data strongly support the specific status of these two forms. We suggest that smooth cystacanths correspond to P. laevis, whereas wrinkled cystacanths might correspond to the previously described and poorly documented, Pomphorhynchus tereticollis, considered a synonym of P. laevis. This study also confirms the value of a joint analysis of internal transcribed spacers and cytochrome c oxidase subunit 1 genes to biogeographic studies on these species. Finally, we emphasize the importance of linking morphological and biological characteristics of acanthocephalan cystacanths to molecular data, in the study of the evolutionary ecology and systematics of this group.

The aim of this paper was to test the hypothesis that when the 2 species of AcanthocephalanPomphorhynchus laevisandAcanthocephalus clavulaare found concurrently within the intestine of brown trout under field conditions, they have the potential to interact negatively. Evidence has shown that Acanthocephala are more likely to exhibit negative interactions with their own and other species, under both field and experimental conditions. Furthermore, the likelihood of these interactions is increased in Ireland because of the absence of certain definitive hosts and the fact that concurrent infections by two or more species of Acanthocephala are more commonly observed in fish. Data collected from wild and stocked brown trout and from 2 lakes provided an opportunity to compare the 2 potentially interacting helminth species in their fundamental and realized niche and several pieces of convincing evidence are provided here to support the hypothesis. A significant negative association between the numbers of each species found in individual fish was reported and this was consistent for both wild and stocked trout. Furthermore, an analysis of the proportions of low, moderate and high intensity infections in single and concurrent infections revealed a significant reduction in increasing intensities in concurrent infections compared to single infections. Finally, strikingly different patterns of niche inhabitation were observed, particularly forP. laevisin the presence ofA. clavulain wild trout. Results from the niche width analysis also support the observations on average position in single and concurrent infections. The niche width ofP. laeviswhen it co-occurred withA. clavuladecreased markedly in high intensity infections compared to low intensity infections.

In a small isolated lake in Slovakia, the fish acanthocephalan Pomphorhynchus laevis using Gammarus balcanicus and the minnow Phoxinus phoxinus, respectively, as its intermediate and final hosts, represented a dominant helminth species. Its prevalence and intensity of infection in fish showed no significant variation during a year fluctuating above the mean values of 89 % and 6.6 worms per fish. The mean prevalence of P. laevis larvae in Gammarus was 41.4 % with a maximum in the late summer and autumn ; individual crustaceans were infected by 1-9 larvae. There was one generation of P. laevis per year. Following up an annual cycle, an occurrence of new infections of Gammarus culminated in October and in the next May for Phoxinus. The sex ratios of both the adults and larvae of acanthocephalans were near unity but favoured slightly males in spring and autumn. The distribution of P. laevis in minnows and crustaceans was highly aggregated and fitted with the negative binomial model. The spatial distribution analysis of parasites along the fish alimentary tract showed a clear preference of P. laevis for its proximal half, with the maximum numbers in the site of the first intestinal loop. Immature worms of both sexes predominated in the proximal region and moved slightly down the alimentary tract during their growth and maturation.

The acanthocephalan parasite Pomphorhynchus laevis is transmitted by a suitable intermediate host such as the amphipod Gammarus pulex to its definitive fish host. Parasite-induced alterations in both appearance and behaviour concur to render infected gammarids more vulnerable to predation, thus promoting parasite transmission. Experimental infection of laboratory bred full- and half-sib groups of three-spined sticklebacks (Gasterosteus aculeatus) provided evidence that the parasite imposes a survival cost proportional to the severity of infection on its final host. Variation among sibships in the susceptibility to infection was consistent. When given a choice, fish consumed significantly more infected than uninfected prey. Overall, more resistant fish did not prey upon infected gammarids more often than did relatively susceptible fish. Only fish with a relatively high physical condition properly adjusted prey selection to the extent of their parasite susceptibility, thus exploiting the enhanced profitability of infected prey.

Background Several parasites with complex life-cycles induce phenotypic alterations in their intermediate hosts. According to the host manipulation hypothesis, such phenotypic alterations are supposed to increase the fitness of the parasite at the expense of that of its intermediate hosts through increasing the probability of transmission to next hosts. Although the phenomenon has received a large attention, the proximate factors modulating the occurrence and intensity of host manipulation remain poorly known. It has however, been suggested that the amount of energy reserves in the intermediate host might be a key parameter, although its precise influence on the intensity of manipulation remains unclear. Dietary depletion in the host may also lead to compromise with other parasite traits, such as probability of establishing or growth or virulence. Methods Here, we address the question through performing experimental infections of the freshwater amphipod Gammarus pulex with two different populations of the acanthocephalan fish parasite Pomphorhynchus laevis, and manipulation of host nutritional condition. Following exposure, gammarids were given either a “standard” diet (consisting of elm leaves and chironomid larvae) or a “deprived” food treatment (deprived in proteins), and infection parameters were recorded. Once parasites reached the stage at which they become infective to their definitive host, refuge use (a behavioural trait presumably implied in trophic transmission) was assessed, and metabolic rate was measured. Results Infected gammarids exposed to the deprived food treatment showed a lower metabolic rate, indicative of a lower body condition, compared to those exposed to the standard food treatment. Parasite size was smaller, and, depending on the population of origin of the parasites, intensity of infection was lower or mortality was higher in deprived hosts. However, food treatment had no effect on either the timing or intensity of behavioural modifications. Conclusions Overall, while our results suggest that acanthocephalan parasites develop better in hosts in good condition, no evidence was found for an influence of host nutritional condition on host manipulation by parasites.

Intestinal mucous cell numbers and their glycoconjugate composition were investigated by histochemical methods in uninfected chub, Squalius cephalus , and in conspecifics naturally parasitised with the acanthocephalan Pomphorhynchus laevis . A sub-population of 42 chub from the River Tiber (Perugia, Italy) were sampled and screened for ecto and endoparasites. No parasites were found in gills and in other visceral organs of chub and P. laevis appeared to be the only enteric worm encountered. In all infected chub (twenty-eight out of 42) this acanthocephalan was encountered mainly in the mid-gut. In situ , an excessive yellowish mucus or catarrh was observed around each acanthocephalan. Hyperplasia and hypertrophy of the mucous cells were only evident near the site of P. laevis attachment where the total number of mucous cells and the number of those containing acidic, particularly non-sulphated mucins, or mixed glycoconjugates were significantly higher. In intestinal regions of infected fish far away from the point of parasite attachment, there were no statistical differences in the density of mucous cells in comparison to uninfected fish. Interestingly, in parasitised chub, the length of intestinal folds was significantly larger close to the sites at which P . laevis attach when compared to the length of the intestinal folds located further away from the acanthocephalans and/or in uninfected intestines. The effect of P. laevis on intestinal mucous cells of S. cephalus was compared to other parasite–host systems and the role of enhanced mucus production in parasitized intestines was discussed.

A series of ultrastructural-based studies were conducted on the interface region in different fish–helminth systems: (a) an intestinal infection of the cestode Monobothrium wageneri in tench, Tinca tinca; (b) an extensive intestinal submucosa and mucosal infection in tench by metacercariae of an unidentified digenean trematode; (c) an intestinal infection in brown trout, Salmo trutta, by the acanthocephalan Dentitruncus truttae; (d) an extraintestinal infection by larvae of the acanthocephalan, Pomphorhynchus laevis in three-spined sticklebacks, Gasterosteus aculeatus; and (e) an infection in the livers of Eurasian minnow, Phoxinus phoxinus, by larvae of the nematode Raphidascaris acus. Endoparasitic helminths frequently cause inflammation of the digestive tract and associated organs, inducing the recruitment of various immune cells to the site of infection. In each of the fish–helminth systems that were studied, a massive hyperplastic granulocyte response involving mast cells (MCs) and neutrophils in close proximity to the helminths was documented. The current study presents data on the interface region in each fish–helminth system and documents the penetration of mast cells granules within the tegument of P. laevis larvae. No extracellular vesicles containing tegumental secretions from any of the four different taxa of endoparasitic helminths species at the host–parasite interface region were seen.

Background In vertebrates, the presence of enteric worms can induce structural changes to the alimentary canal impacting on the neuroendocrine system, altering the proper functioning of the gastrointestinal tract and affecting the occurrence and relative density of endocrine cells (ECs). This account represents the first immunohistochemistry and ultrastructure-based study which documents the intimate relationship between the intestinal mucous cells and ECs in a fish-helminth system, investigating the potential effects of enteric neuromodulators on gut mucus secretion/discharge. Methods A modified dual immunohisto- and histochemical staining technique was applied on intestinal sections from both infected and uninfected fish. Sections were incubated in antisera to a range of neuromodulators (i.e. leu-enkephalin, met-enkephalin, galanin and serotonin) and the glycoconjugate histochemistry of the mucous cells was determined using a subsequent alcian blue – periodic acid Schiff staining step. Dual fluorescent staining on sections prepared for confocal laser scanning microscopy and transmission electron microscopy were also used to document the relationship between ECs and mucous cells. Results From a total of 26 specimens of Squalius cephalus sampled from the River Paglia, 16 (i.e. 62 %) specimens were found to harbour an infection of the acanthocephalan Pomphorhynchus laevis (average intensity of infection 9.2 ± 0.8 parasites host−1, mean ± standard error). When acanthocephalans were present, the numbers of mucous cells (most notably those containing acidic or mixed glycoconjugates) and ECs secreting leu-enkephalin, met-enkephalin, galanin, serotonin were significantly higher than those seen on sections from uninfected fish. The relationship between met-enkephalin-like or serotonin-like ECs and lectin DBA positive mucous cells was demonstrated through a dual fluorescent staining. The presence of tight connections and desmosomes between mucous and ECs in transmission electron micrographs provides further evidence of this intimate relationship. Conclusions The presence of P. laevis induces an increase in the number of enteric ECs that are immunoreactive to leu- and met-enkephalin, galanin, and serotonin anti-sera. The mucous cells hyperplasia and enhanced mucus secretion in the helminth-infected intestines could be elicited by the increase in the number of ECs which release these regulatory substances.

Here we report the genetic variability and presence of mtDNA-like sequences of Pomphorhynchus laevis from the chub, Squalius cephalus, caught at the sampling sites along the Sava River and its tributary the Sutla River in Croatia. Sequences of the cytochrome c oxidase subunit 1 (COI) gene of the recovered P. laevis specimens were used for haplotype network construction and phylogenetic analysis. These analyses showed that some specimens contained mitochondrial-like sequences, and they uncovered the existence of a Sava River basin strain different from known strains of P. laevis. This is the first time that P. laevis has been shown to contain mtDNA-like sequences, suggesting the need to exercise caution during COI analyses of P. laevis using universal primers. Highly conserved sequences of two nuclear markers, the ITS region and 18S rRNA, were not helpful for understanding genetic variability or differentiating strains. Furthermore, analysis of the dynamics of P. laevis infections in S. cephalus from the Sava and Sutla Rivers showed decreased prevalence and abundance at sites with inferior water quality, positive association of parasite abundance with fish size, and no clear association of parasite abundance with fish condition index or sex.

This experimental study assessed the role of the microhabitat in the uptake of metals by adult acanthocephalans. We examined the accumulation of lead by adult Pomphorhynchus laevis in the intestine of chub (Leuciscus cephalus) and compared it with that in goldfish, Carassius auratus auratus, in which the parasites penetrate the intestinal wall and enter the body cavity. Chub and goldfish experimentally infected with adult Pomphorhynchus laevis were exposed to 0.01 mg l(-1) Pb(2+) over 3 weeks. Lead was rapidly accumulated in the intestinal acanthocephalans reaching a mean concentration of 7.3 microg g(-1). This concentration was significantly greater than in the host muscle, liver and intestine and more than 730 times higher than the exposure concentration. Intraperitoneal P. laevis in goldfish exposed to lead did not accumulate the metal. Thus, it was conclusively shown that metal accumulation in acanthocephalans is associated with the intestinal location and does not occur in the body cavity.

Besides conspicuous changes in behaviour, manipulative parasites may also induce subtle physiological effects in the host that may also be favourable to the parasite. In particular, parasites may be able to influence the re-allocation of resources in their own favour. We studied the association between the presence of the acanthocephalan parasite, Pomphorhynchus laevis, and inter-individual variation in the lipid and glycogen content of its crustacean host, Gammarus pulex (Amphipoda). Infected gravid females had significantly lower lipid contents than uninfected females, but there was no difference in the lipid contents of non-gravid females and males that were infected with P. laevis. In contrast, we found that all individuals that were parasitised by P. laevis had significantly increased glycogen contents, independent of their sex and reproductive status. We discuss our results in relation to sex-related reproductive strategies of hosts, and the influence they may have on the level of conflict over energy allocation between the host and the parasite.

When two parasite species are manipulators and have different definitive hosts, there is a potential for conflict between them. Selection may then exist for either avoiding hosts infected with conflicting parasites, or for hijacking, i.e. competitive processes to gain control of the intermediate host. The evidence for both phenomena depends largely on the study of the relative competitive abilities of parasites within their common intermediate host. We studied the effects of simultaneous infection by a fish acanthocephalan parasite, Pomphorhynchus laevis, and a bird acanthocephalan parasite, Polymorphus minutus, on the behaviour of their common intermediate host, the amphipod Gammarus pulex. We compared the reaction to light and vertical distribution of individuals infected with both parasites to those of individuals harbouring a single parasite species and uninfected ones under controlled conditions. Compared to uninfected gammarids that were photophobic and tended to remain at the bottom of the water column, P. laevis-infected gammarids were attracted to light, whereas P. minutus-infected individuals showed a modified vertical distribution and were swimming closer to the water surface. The effects of both P. laevis and P. minutus appeared to be dependent only on their presence, not on their intensity. Depending on the behavioural trait under study, however, the outcome of the antagonism between P. laevis and P. minutus differed. The vertical distribution of gammarids harbouring both parasites was half-way between those of P. laevis- and P. minutus-infected individuals, whereas P. laevis was able to induce altered reaction to light even in the presence of P. minutus. We discuss our results in relation to the occurrence of active avoidance or hijacking between conflicting manipulative parasites and provide some recommendations for future research.

Sures, B., and Siddall, R. 1999. Pomphorhynchus laevis: The intestinal acanthocephalan as a lead sink for its fish host, chub (Leuciscus cephalus). Experimental Parasitology93, 66–72. Aqueous lead exposure of chub (Leuciscus cephalus) experimentally infected with the parasite Pomphorhynchus laevis resulted in a rapid accumulation of this metal in the intestinal acanthocephalans, reaching concentrations which were significantly greater than in the host muscle, liver, and intestine and approximately 1000 times higher than the exposure con centration. Parasitized chub accumulated significantly less lead in their intestinal wall than their uninfected conspecifics (Mann-Whitney U test, P ≤ 0.05). From in vitro studies it was shown that lead uptake of P. laevis cystacanths clearly increases by adding 1% eel bile to a commercial RMPI-1640 medium containing 0.1 μg ml−1 Pb2+ compared to the controls, which were maintained in RMPI-1640 medium containing lead at the same concentration but without bile. It is therefore most likely that P. laevis in chub absorb bile-bound lead from the host intestine and thus reduce its reabsorption by the intestinal wall, thereby interrupting the hepatic–intestinal cycling of the metal. This is the first example of a beneficial impact of a parasite on its host.

The composition of the parasite fauna of the flounder,Platichthys flesus, retrieved from two locations in the tidal Thames is described in detail for the first time. The combined parasite species list of the flounders from Lots Road in the upper tideway and West Thurrock in the middle tideway consisted of one protozoan (Glugea stephani), one monogenean (Gyrodactylussp.), four larval digeneans (Cryptocotyle concava,Timoniella imbutiforme,T. praeterita, andLabratrema minimus), five adult digeneans (Derogenes varicus,Lecithaster gibbosus,Podocotylesp.,Plagioporus varius, andZoogonoides viviparus), one larval cestode (unidentified tetraphyllidean), one or possibly more larval nematodes (unidentified) plus five adult nematodes (Capillariasp.,Cucullanus heterochrous,C. minutus,Contracaecumsp. andGoeziasp.), two acanthocephalans (Pomphorhynchus laevisandAcanthocephalus anguillae), three copepods (Lepeophtheirus pectoralis,Acanthochondriasp. andLernaeocera branchialis), and one mollusc (unidentified glochidia). The overall parasite community of flounders from Lots Road and West Thurrock were compared in terms of species richness and diversity. The parasite community in flounders from the former location in the upper tideway was found to be less diverse than that of its counterpart at West Thurrock in the middle estuary. The component community of Lots Road flounders was dominated by the acanthocephalanPomphorhynchus laevis.

Zoographical distribution of metazoan fish parasites in herring, Clupea harengus, from the Baltic Sea was analysed in order to use them as potential biological indicators. A total of 210 herring from six different sampling sites were investigated, harbouring 12 different parasite species [five digeneans (D), one cestode (C), three nematodes (N) and three acanthocephalans (A)]. The distribution of the parasite species differed according to region, with a distinct gradient of decreasing species richness towards the east of the Baltic Sea. The western localities at Kiel Bay, Rügen and Poland had the highest parasite diversity, including the marine parasite species Anisakis simplex (s.s.) (N), Brachyphallus crenatus and Hemiurus luehei (both D). The eastern localities had low parasite species richness, predominated by the freshwater digenean Diplostomum spathaceum. We could identify three different Baltic herring stocks, the spring-spawning herring of the western Baltic reaching from the Kattegat to the German and Polish coast, the stock of the central Baltic proper and the northern stock of C. harengus var. membras of the Gulf of Finland. The limited distribution of the herring parasites within the Baltic Sea enables their use as biological indicators for migration patterns and stock separation. The acanthocephalan Pomphorhynchus laevis that has already been used as an accumulation bioindicator for heavy metals was only recorded for the western herring stocks. However, the presence of mainly generalistic parasites and their uneven distribution patterns make their use as indicators for regional environmental and global change more difficult.

6 pages; International audience; Larvae of many trophically-transmitted parasites alter the behaviour of their intermediate host in ways that increase their probability of transmission to the next host in their life cycle. Before reaching a stage that is infective to the next host, parasite larvae may develop through several larval stages in the intermediate host that are not infective to the definitive host. Early predation at these stages results in parasite death, and it has recently been shown that non-infective larvae of some helminths decrease such risk by enhancing the anti-predator defences of the host, including decreased activity and increased sheltering. However, these behavioural changes may divert infected hosts from an optimal balance between survival and foraging (either seeking food or a mate). In this study, this hypothesis was tested using the intermediate host of the acanthocephalan parasite Pomphorhynchus laevis, the freshwater amphipod Gammarus pulex. We compared activity, refuge use, food foraging and food intake of hosts experimentally infected with the non-infective stage (acanthella), with that of uninfected gammarids. Behavioural assays were conducted in four situations varying in predation risk and in food accessibility. Acanthella-infected amphipods showed an increase in refuge use and a general reduction in activity and food intake. There was no effect of parasite intensity on these traits. Uninfected individuals showed plastic responses to water-borne cues from fish by adjusting refuge use, activity and food intake. They also foraged more when the food was placed outside the refuge. At the intra-individual level, refuge use and food intake were positively correlated in infected gammarids only. Overall, our findings suggest that uninfected gammarids exhibit risk-sensitive behaviour including increased food intake under predation risk, whereas gammarids infected with the non-infective larvae of P. laevis exhibit a lower motivation to feed, irrespective of predation risk and food accessibility.

An examination of the effects of Pomphorhynchus laevis cystacanths on the haemolymph and midgut gland carbohydrate titres of its intermediate host, Gammarus pulex (Crustacea) was undertaken. In the haemolymph, infection with cystacanths did not alter the relationship between haemolymph carbohydrate titres and body wet weight. However, in the midgut glands, infection did alter the relationship between gammarid wet weight and titres of glucose and trehalose (P

In this research, a total of 298 Eurasian marsh frogs, Pelophylax ridibundus (Pallas, 1771) were collected from different localities in Denizli province (Inner-west Anatolia Region, the eastern part of Aegean Region) Turkey between 2006 and 2009 and examined for helminths. Of 262 (87.91 %) Pelophylax ridibundus samples were infected with one or more helminths. Pelophylax ridibundus harbored eight species of digeneans (Diplodiscus subclavatus, Gorgoderina vitelliloba, Gorgodera cygnoides, Pleurogenoides medians, Prosotocus confusus, Skrjabinoeces breviansa, Encyclometra colubrimurorum and Ophistoglyhe ranae), one species of cestode (Nematotaenia dispar), two species of acanthocephalans (Acanthocephalus ranae and Pomphorhynchus laevis), and six species of nematodes (Rhabdias bufonis, Oswaldocruzia filiformis, Cosmocerca ornata, Oxysomatium brevicaudatum, Eustrongylides sp. and Abbreviata sp.). P. ridibundus represents a host record for Nematotaenia dispar in Turkey.

The fatty acid fingerprints of total lipid extracts from the four fish parasites Acanthocephalus lucii, Neoechinorhynchus rutili, Paratenuisentis ambiguus, and Pomphorhynchus laevis were investigated by capillary gas-liquid chromatography (GLC). The fatty acid patterns of the parasites were compared with those of their respective host tissue, viz., intestinal tract tissue of infected perch, brown trout, eel, and chub. The highly complex gas chromatograms revealed significant differences not only between parasite and host tissue but also between the parasites themselves. For instance, all the parasites contained much more eicosapentaenoic acid (20:5n-3) than did the respective fish intestinal tissue. Differences were also observed between the presoma and metasoma of Pomphorhynchus laevis.

Background Parasites often face a trade-off between exploitation of host resources and transmission probabilities to the next host. In helminths, larval growth, a major component of adult parasite fitness, is linked to exploitation of intermediate host resources and is influenced by the presence of co-infecting conspecifics. In manipulative parasites, larval growth strategy could also interact with their ability to alter intermediate host phenotype and influence parasite transmission. Methods We used experimental infections of Gammarus pulex by Pomphorhynchus laevis (Acanthocephala), to investigate larval size effects on host behavioural manipulation among different parasite sibships and various degrees of intra-host competition. Results Intra-host competition reduced mean P. laevis cystacanth size, but the largest cystacanth within a host always reached the same size. Therefore, all co-infecting parasites did not equally suffer from intraspecific competition. Under no intra-host competition (1 parasite per host), larval size was positively correlated with host phototaxis. At higher infection intensities, this relationship disappeared, possibly because of strong competition for host resources, and thus larval growth, and limited manipulative abilities of co-infecting larval acanthocephalans. Conclusions Our study indicates that behavioural manipulation is a condition-dependant phenomenon that needs the integration of parasite-related variables to be fully understood.

9 pages; International audience; Few endoparasite species are pigmented. Acanthocephalans are an exception however, with several species being characterised by yellow to orange colouration both at the immature (cystacanth) and adult stages. However, the functional and adaptive significance of carotenoid-based colourations in acanthocephalans remains unclear. One possibility is that the carotenoid content of acanthocephalan cystacanths acts as a protective device against ultra-violet radiation (UVR) passing through the translucent cuticle of their crustacean hosts. Indeed, acanthocephalans often bring about behavioural changes in their aquatic intermediate hosts that can increase their exposure to light. Carotenoid composition and damage due to ultra-violet - B (UVB) radiation were investigated in three acanthocephalan parasite species that induce contrasting behavioural alterations in their common intermediate host, the crustacean amphipod Gammarus pulex. The fish acanthocephalans Pomphorhynchus laevis and Pomphorhynchus tereticollis both induce a positive phototaxis in gammarids, such that infected hosts spend more time out of shelters, while remaining benthic. The bird acanthocephalan Polymorphus minutus, on the other hand, induces a negative geotaxis, such that infected hosts typically swim close to the water surface, becoming more exposed to UV radiation. We show that differences in cystacanth colouration between acanthocephalan species directly reflect important differences in carotenoid content. The two fish parasites exhibit a contrasting pattern, with P. tereticollis harbouring a large diversity of carotenoid pigments, whereas P. laevis is characterised by a lower carotenoid content consisting mainly of lutein and astaxanthin. The highest carotenoid content is found in the bright orange P.minutus, with a predominance of esterified forms of astaxanthin. Exposure to UVB radiation revealed a higher susceptibility in P. laevis larvae compared with P. tereticollis and P. minutus, in terms of sublethality (decreased evagination rate) and of damage to DNA (increased cyclobutane pyrimidine dimers production). Although we found important and correlated interspecific differences in carotenoid composition and tolerance to high UVB radiation, our results do not fully support the hypothesis of adaptive carotenoid-based colourations in relation to UV protection. An alternative scenario for the evolution of carotenoid accumulation in acanthocephalan parasites is discussed.

SUMMARYLarval helminths exploit the physiology of their intermediate hosts: first, as a resource for energy and space and second by altering the immune system activity to ensure their survival. Whereas the growth pattern under parasite competition has been investigated, the effect of multiple infections on the level of parasite-induced immunodepression in a trophically transmitted helminth has been neglected. In this study, amphipodsGammarus pulexwere infected in the laboratory by the acanthocephalanPomphorhynchus laevisto investigate how parasite density in the intermediate host affected (i) cystacanth growth and (ii) the level of parasite-induced alterations of the host immune defences, two traits strongly linked to host exploitation. The study highlights that sharing a host is costly. As parasite intensity increases, competition for resources translates into a reduction in cystacanth volume. Immune manipulation is also modulated by density. Interestingly, immunodepression is higher in double-infected hosts compared to hosts with a single infection, suggesting an opportunity for cooperative immune manipulation. However, in higher multiple infections, parasites do not further down-regulate the host immune response, possibly to avoid additional costs that may outweigh the benefits of immunodepression.

SUMMARYComparisons were made between the protein concentrations and protein profiles of uninfected Gammarus pulex and those infected with cystacanths of Pomphorhynchus laevis. Comparisons of the extractable haemolymph volumes from uninfected and infected G. pulex, when related to host tissue weight, showed that there was no difference in the host tissue/haemolymph volume ratio between infected and uninfected individuals. SDS-PAGE of haemolymph samples resolved 36 bands of protein, the major components being band 6(19 kDa) and 21(33 kDa). Densitometric analysis of haemolymph samples showed that infected gammarids had total protein concentrations elevated by 84%. The (88 kDa) subunit was identified as the monomer of the respiratory protein haemocyanin. This band was significantly elevated in infected individuals (one-way ANOVA P < 0.001); increasing from 30 to 45% of the total haemolymph proteins.

SUMMARYConcentrations of the elements As, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, Sn, V, Zn were analysed by inductively coupled plasma mass spectrometry (ICP-MS) in the acanthocephalan Pomphorhynchus laevis and its fish host Barbus barbus. A total of 27 barbels were collected from the Danube River in autumn 2006 close to the town Kozloduy (685 river kilometer) on the Bulgarian river bank. Fish were divided into 3 groups. According to their P. laevis infrapopulation size hosts were considered as heavily infected (>100 worms per fish) and lightly infected (P. laevis. The 5 elements As, Cd, Cu, Pb and Zn were detected in significantly higher concentrations in parasites compared to host tissues (muscle, intestine, liver). According to the calculated mean bioconcentration factors, 3 more elements (Co, Mn, V) showed usually higher concentrations in P. laevis. Comparisons between heavily and lightly infected fish revealed significant differences only for V with higher concentrations for the heavily infected group. Concerning sex-specific metal accumulation V and Zn showed significant differences (V, at PP=0·05), with higher levels of both metals in females of P. laevis. Our results suggest that – for the metals analysed – the size of the parasite infrapopulation plays no role in the degree of metal accumulation. Similarly, parasite sex seems not to be a crucial factor for metal accumulation in the parasites. Thus, for metal monitoring purposes there is no need to take these aspects into account, which makes the use of parasites as bioindicators more applicable.

SUMMARYBiological invasions expose parasites to new invasive hosts in addition to their local hosts. However, local parasites are often less successful in infecting and exploiting their new hosts. This may have major consequences for the competitive ability of hosts, and finally on the fate of the parasite-host community. In Burgundy (Eastern France), the acanthocephalan parasite,Pomphorhynchus laevis, infects 2 amphipod species living in sympatry: the nativeGammarus pulexand the invasiveGammarus roeseli. WhileP. laevisaffects the behaviour and the immunity ofG. pulex,G. roeseliseems unaffected by the infection. In this study, we examined in detail the ability of the parasite to affect the immune system and resource storage of both gammarid species. We found that the infection was associated with a general decrease of the prophenoloxidase activity, haemocyte density, resistance to an artificial bacterial infection and level of sugar reserves inG. pulex, but not inG. roeseli. These results demonstrate a differential ability ofP. laevisto exploit its local and its invasive gammarid hosts. Potential mechanisms of these differential physiological alterations and their potential consequences on the coexistence of both gammarid species in sympatry are discussed.