How Ponto-Caspian invaders affect local parasite communities of native fish

Invasive species are a major threat to ecosystems worldwide. Their effects are versatile and mostly well studied. However, not much is known about the impact of invasion on native parasite communities, although parasites are usually important response variables for ecosystem health. To improve the knowledge on how native fish parasite communities and their dynamics are affected by invasive species and how these processes change local host-parasite interactions over time, we studied different host-parasite systems in four German rivers. Three of these rivers (Rhine, Ems, and Elbe) are heavily invaded by different Ponto-Caspian species such as the amphipod Dikerogammarus villosus and various gobiids such as Neogobius melanostomus and Ponticola kessleri that serve as potential hosts for different local parasite species, while the fourth river (Schwentine) was free of any Ponto-Caspian invaders. Due to the lack of additional uninvaded river systems, literature data on parasite communities before invasion were compared with the post invasion status for the rivers Rhine and Elbe. The results showed differences among the parasite communities of different host species from the three invaded rivers when compared to the Schwentine River. Among the local internal parasite communities, especially the acanthocephalan Pomphorhynchus laevis and the nematode Raphidascaris acus have to be considered as key species associated with invasions from the Ponto-Caspian region. As the examined invasive Ponto-Caspian fish species serves as suitable host for both parasite species, the increases in their infection rates in native fish species are examples of parasite spill back (R. acus) and spill over (P. laevis, at least in the river Rhine). These results were further supported by the analysis of literature data on parasite communities of the past 20 years. Consequences for local parasite communities range from decreased prevalence of native parasites towards an extinction of entire parasite species.

Evaluation of architectural and histopathological biomarkers in the intestine of brown trout (Salmo trutta Linnaeus, 1758) challenged with environmental pollution

In the present study novel histopathological approach, using fish intestine as a sensitive bioindicator organ of pollution impact in the freshwater ecosystem, was proposed. Histopathological alterations were compared between native brown trout (Salmo trutta Linnaeus, 1758) from the reference (Krka River spring) and pollution impacted location (influence of technological/municipal wastewaters and agricultural runoff near the Town of Knin) of the karst Krka River in Croatia. In brown trout from both locations, severe parasitic infestation with acanthocephalan species Dentitruncus trutae was found, enabling evaluation of acanthocephalan infestation histopathology, which indicated parasite tissue reaction in a form of inflammatory, necrotic and hyperplastic response that extended throughout lamina epithelialis mucosae, lamina propria, and lamina muscularis mucosae. New semi-quantitative histological approach was proposed in order to foresee alterations classified in three reaction patterns: control tissue appearance, moderate (progressive) tissue impairment and severe (regressive and inflammatory) tissue damage. The most frequent progressive alteration was hyperplasia of epithelium on the reference site, whereas the most frequent regressive alterations were atrophy and necrosis seen on the polluted site. Furthermore, histopathological approach was combined with micromorphological and macromorphological assessment as an additional indicator of pollution impact. Among 15 observed intestinal measures, two biomarkers of intestinal tissue damage were indicated as significant, height of supranuclear space (hSN) and number of mucous cells over 100 μm fold distance of intestinal mucosa (nM), which measures were significantly lower in fish from polluted area compared to the reference site. Obtained results indicated that combined histological and morphological approach on fish intestinal tissue might be used as a valuable biological tool for assessing pollution impact on aquatic organisms. Therefore, semi quantitative scoring and multiparametric morphological assessment of intestinal tissue lesion magnitude should become a common approach to handle environmental pollution impact.

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.

ACANTHOCEPHALANS PROSTHENORCHIS CF. ELEGANS (ARCHIACANTHOCEPHALA: OLIGACANTHORHYNCHIDAE), PARASITES OF PRIMATES IN THE MOSCOW ZOO

Acanthocephalans Prosthenorchis cf. elegans were found in primates in the Moscow Zoo. The larvae of these parasites (cistacanths) were found in cockroaches Blattella germanica that had been captured near aviaries of infected animals. Descriptions and drawings of adult parasites and their larvae are given. Analysis of Prosthenorchis cf. elegans genes ITS 1 rDNA and CO 1 mtDNA shows phylogenetic relations of these parasites with several representatives of the class Archiacanthocephala. The obtained molecular data, however, do not support the monophyly of the family Oligacanthorhynchidae and the order Oligacanthorhynchida.

Host-parasite relationships as determinants of heavy metal concentrations in perch (Perca fluviatilis) and its intestinal parasite infection

The concentrations of As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn and their bioconcentration factors (BCFs) were determined in two intestinal parasites, an acanthocephalan, Acanthocephalus lucii, a tapeworm, Proteocephalus percae, present in the same host, the European perch (Perca fluviatilis, L.), in the heavily polluted Ružín reservoir in eastern Slovakia. The bioaccumulation of heavy metals in the fish organs and parasites was studied for acanthocephalan and tapeworm monoinfections or mixed infections by the two parasites and for the size of their parasitic infrapopulations. Bioconcentration factors (c[parasite]/c[muscle tissue]) showed that the concentrations of As, Ni, Pb and Zn were higher in mixed infections than in monoinfections. Negative correlations between heavy metal concentrations in perch organs and the parasites were found. For example, higher concentrations of Ni and Zn in both parasite species corresponded with lower metal concentrations in perch and hard roe. Likewise, significant negative relationships between metal concentrations in fish organs and number of parasites were noticed with lower levels of Pb in fish harbouring higher numbers of tapeworms. Similarly, in both parasite species the concentrations of some essential elements (Cr, Mn) were lower at high infection intensities compared to low intensities. Our study revealed that the differential concentration of heavy metals in perch organs was affected by the type of infection (mono- or mixed-infection), and needs to be considered in field ecotoxicological and parasitological studies as a potentially important factor influencing the pollutant concentrations in fish.

Transcriptome data reveal Syndermatan relationships and suggest the evolution of endoparasitism in Acanthocephala via an epizoic stage

The taxon Syndermata comprises the biologically interesting wheel animals ("Rotifera": Bdelloidea + Monogononta + Seisonidea) and thorny-headed worms (Acanthocephala), and is central for testing superordinate phylogenetic hypotheses (Platyzoa, Gnathifera) in the metazoan tree of life. Recent analyses of syndermatan phylogeny suggested paraphyly of Eurotatoria (free-living bdelloids and monogononts) with respect to endoparasitic acanthocephalans. Data of epizoic seisonids, however, were absent, which may have affected the branching order within the syndermatan clade. Moreover, the position of Seisonidea within Syndermata should help in understanding the evolution of acanthocephalan endoparasitism. Here, we report the first phylogenomic analysis that includes all four higher-ranked groups of Syndermata. The analyzed data sets comprise new transcriptome data for Seison spec. (Seisonidea), Brachionus manjavacas (Monogononta), Adineta vaga (Bdelloidea), and Paratenuisentis ambiguus (Acanthocephala). Maximum likelihood and Bayesian trees for a total of 19 metazoan species were reconstructed from up to 410 functionally diverse proteins. The results unanimously place Monogononta basally within Syndermata, and Bdelloidea appear as the sister group to a clade comprising epizoic Seisonidea and endoparasitic Acanthocephala. Our results support monophyly of Syndermata, Hemirotifera (Bdelloidea + Seisonidea + Acanthocephala), and Pararotatoria (Seisonidea + Acanthocephala), rejecting monophyly of traditional Rotifera and Eurotatoria. This serves as an indication that early acanthocephalans lived epizoically or as ectoparasites on arthropods, before their complex lifecycle with arthropod intermediate and vertebrate definite hosts evolved.

[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.

Parasites of juvenile brook trout (Salvelinus fontinalis) from Hunt Creek, Michigan

Four parasite species (Crepidostomum cooperi, Cystidicoloides ephemeridarum, Acanthocephalus dirus, Salmincola edwardsii) infected 215 juvenile brook trout (105 young-of-year; 110, 1-yr-old) from Hunt Creek, Michigan, in 2003, 2004, and 2005. Prevalences of these species in 2004 (main study year) varied from 29 to 37%. Crepidostomnum cooperi had the highest mean intensity and mean abundance, followed by C. ephemeridarum. The number of fish infected with each parasite species was significantly higher in 1-yr-old fish than in young-of-year fish. Also, the mean intensities and mean abundances of C. cooperi and C. ephemeridarum and the mean abundance of A. dirus were significantly higher in older fish. The mean intensity of C. cooperi and prevalence of A. dirus were significantly higher in fish between creek sections. Fish length had a significant positive effect on the abundances of C. cooperi and C. ephemeridarum; parasite species richness, on the abundances of A. dirus and S. edwardsii; and parasite species richness in the 2003 and 2004 trout cohorts, respectively. Crepidostomum cooperi, C. ephemeridarum, A. dirus, and S. edwardsii commonly infect Michigan brook trout. The small number of parasite species infecting Hunt Creek brook trout is similar to the number of parasite species of brook trout from other Michigan creeks.

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.

Sexual differences in larval life history traits of acanthocephalan cystacanths

Sexual differences in life history traits, such as size dimorphism, presumably arise via sexual selection and are most readily observed in adults. For complex life-cycle parasites, however, sexual selection may also have consequences for larval traits, e.g., growth in intermediate hosts. Two acanthocephalan species (Acanthocephalus lucii and Echinorhynchus borealis) were studied to determine, whether larval life histories differ between males and females. The size of female A. lucii cystacanths had a much stronger relationship with intermediate host size than males, suggesting females invest more in growth and are consequently more limited by resources. No relationship between host size and cystacanth size was observed for E. borealis. For both species, female cystacanths survived longer in a culture medium composed entirely of salts, which could suggest that females have greater energy reserves than males. A comparative analysis across acanthocephalan species indicated that sexual size dimorphism at the adult stage correlates with cystacanth dimorphism. However, the relationship was not isometric; cystacanths do not reach the same level of sexual dimorphism as adults, possibly due to resource constraints. Our results suggest that larval life histories diverge between males and females in some acanthocephalans, and this is seemingly a consequence of sexual selection acting on adults.

Helminths of the two mountain frogs, banded frog, Rana camerani Boulenger, 1886 and Uludağ frog Rana macrocnemis Boulenger, 1885 (Anura: Ranidae), collected from the Antalya province

In this study, two mountain frogs (Rana camerani and Rana macrocnemis) were collected in the Antalya Province in south-western Turkey during 2001 and 2002 and were examined for helminths. Out of 15 Rana camerani, 10 (66.7%) were infected with 1 or more helminths and out of 20 Rana macrocnemis, 17 (85%) were infected with 1 or more helminths. The helminth fauna of Rana camerani included 4 species of which were 3 trematode species (Haplometra cylindracea, Pleurogenoides medians, Opisthioglyphe rastellus), and 1 nematode species (Cosmocerca ornata). The helminth fauna of Rana macrocnemis included 3 species with 1 trematode species (H. cylindracea), 1 nematode species (C. ornata), and 1 acanthocephalan species (Acanthocephalus ranae). H. cylindracea and C. ornata were observed in both of the mountain frogs.

VIRULENCE OF CORYNOSOMA CONSTRICTUM (ACANTHOCEPHALA: POLYMORPHIDAE) IN HYALELLA AZTECA (AMPHIPODA) THROUGHOUT PARASITE ONTOGENY

Development and growth of parasites depend on resources provided by the host and the parasite's ability to use them. Identifying specific costs incurred by the host provides insight for assessment of parasite energy budgets, which differ among taxa and ontogenetic stages. Data from this study were analyzed using an accelerated failure-time model with intensity as a covariate. Results indicated significantly reduced survival of amphipods, Hyalella azteca, infected with the acanthocephalan Corynosoma constrictum compared with uninfected controls. Male and female amphipod survivorship and infection intensity did not differ; however, amphipods with high-intensity infections (> 16 larvae) died earlier compared with amphipods with low-intensity infections (< 3 larvae). The majority of infected amphipods died between 12 and 24 days postexposure, a period of rapid larval development. It is hypothesized that host death may be due either to an increase in overall larval nutritional demands or to parasite-mediated depletion of a specific host substance. Results from this study suggest that developing C. constrictum satisfies energy requirements by depriving amphipod hosts of resources normally used for somatic growth and maintenance.

GEOGRAPHIC ANALYSIS OF HOST USE, DEVELOPMENT, AND HABITAT USE OF AN ACANTHOCEPHALAN SPECIES, LEPTORHYNCHOIDES THECATUS

Leptorhynchoides thecatus (Linton, 1891), an acanthocephalan parasite of freshwater fishes, varies in host use, development, and habitat use throughout North America. Spatial structure of these characteristics was examined from data extracted from the literature. Geographic patterns were inferred from point comparisons using correllograms and then tested with Moran's I statistic for global and local significance, and visually from regional means within major river drainages. Species of Micropterus Lacepède, 1802 (black basses) were common hosts in most regions, except the Lower Mississippi and South Atlantic regions where species of Lepomis Rafinesque, 1819 (sunfishes) were common hosts. Development, described as the proportions of adults relative to cystacanths (extraintestinal juveniles), decreased with latitude. Habitat use of L. thecatus showed marked geographic patterns. Leptorhynchoides thecatus occurred in the intestine of sunfishes in the South Atlantic and Lower Mississippi regions, in the ceca in fish of all species included in the study in the Missouri and Texas-Gulf regions, and both in ceca and intestines in fish of all species in northern regions. Leptorhynchoides thecatus showed geographic patterning within the variable traits across the range of the species. These patterns may be the result of ecological factors or of genetic differences that might indicate L. thecatus comprises multiple cryptic species.

Neoechinorhynchus curemai (Acanthocephala: Neoechinorhynchidae) in Prochilodus lineatus (Osteichthyes: Prochilodontidae) from the Paraná River, Brazil

This work evaluated parasitic infections by Neoechinorhynchus curemai (Acanthocephala: Neoechinorhynchidae) in Prochilodus lineatus captured between August 2000 and August 2001 in the Paraná River, Presidente Epitácio, São Paulo, Brazil. Of 87 fishes examined, 59 were infected (25 males and 34 females). High mean intensities occurred in August 2000 (45.2, range 2-204), September 2000 (28.5, range 11-73), October 2000 (59.3, range 2-250) and February 2001 (27.3, range 3-73). There was no relationship of rainfall with mean intensity and prevalence. Males were more parasitized (P<0.05) than females. This work contributes to the knowledge of helminth parasites of fish from a little studied region of the Paraná River, showing diversity in their fauna when compared to other places in the same river.

Intra-specific host sharing in the manipulative parasiteAcanthocephalus dirus: does conflict occur over host modification?

The acanthocephalan parasiteAcanthocephalus dirusinduces a colour change in the intermediate host, the aquatic isopodCaecidotea intermedius, which increases transmission to definitive hosts (creek chub, sunfish). We examined the potential for conflict to occur between infective (cystacanth) and non-infective (acanthor, acanthella) stages ofA. dirusover the level of colour modification that should be induced when these stages share a host. Using a field survey, we showed that host sharing by infective and non-infective stages was relatively common and that infective and non-infective stages differed in their effects on colour modification. Non-infective stages induced a colour change over 40% of the body, whereas infective stages induced a colour change over 80%. Thus, conflict could occur between stages over the level of modification that should be induced. We then showed that mixed-stage infections induced a colour change in the host that was consistent with the level of modification induced by the infective stage. We discuss the potential significance of these results to patterns of host modification and their effects on stage-related survival in nature.

Occurrence of Acanthocephalans in Largemouth Bass and Smallmouth Bass (Centrarchidae) From Gull Lake, Michigan

A total of 65 largemouth bass, Micropterus salmoides, and 27 smallmouth bass, M. dolomieu, collected in April-September 2000 and April-July 2001 from Gull Lake, Michigan, were examined for acanthocephalans. Leptorhynchoides thecatus and Neoechinorhynchus cylindratus infected all the bass examined. Leptorhynchoides thecatus had the highest mean intensity (258.2 +/- 185.4 in 2000 and 145.0 +/- 61.0 in 2001) of the species infecting smallmouth bass. Although N. cylindratus had higher mean intensities (42.1 +/- 37.9 in 2000 and 68.9 +/- 70.5 in 2001) than did L. thecatus in largemouth bass, the values were not significantly different between bass species. The prevalence, mean intensity, and mean abundance of Pomphorhynchus bulbocolli in the bass species were below the values for the other acanthocephalan species. Leptorhynchoides thecatus and N. cylindratus are the most abundant intestinal helminths in bass from Gull Lake.

The impact of sexual selection on Corynosoma magdaleni (Acanthocephala) infrapopulations in Saimaa ringed seals (Phoca hispida saimensis)

In free-living animals sexual selection is a central force shaping the spatial distribution of individuals in a population as well as sexual size dimorphism. We studied the influence of sexual selection on spatial distribution, female-to-male body size ratio, and female mating success of acanthocephalans in a natural host population of Saimaa ringed seal (Phoca hispida saimensis) harbouring a single intestinal helminth species, Corynosoma magdaleni. The acanthocephalans were always found along the full length of the small intestine; however, the site selection varied among the individual seals according to the age of the infection. The distribution of male acanthocephalans was not random with respect to females, with larger males tending to aggregate around non-mated females. A higher proportion of C. magdaleni females had copulated in seals with relatively more male worms. Male-male competition for access to females can be intense in C. magdaleni infrapopulation and may select for large males. We found that the larger the infrapopulation size, the smaller the males compared to females. In addition, the greater the female bias in the infrapopulation, the smaller the testes of males. Our study shows that sexual selection may be an important determinant of spatial distribution, male body size and female mating success of C. magdaleni in Saimaa ringed seal.

POSTCYCLIC TRANSMISSION AND ITS EFFECT ON THE DISTRIBUTION OF PAULISENTIS MISSOURIENSIS (ACANTHOCEPHALA) IN THE DEFINITIVE HOST SEMOTILUS ATROMACULATUS

The relationship of fish age class to parasitism by Paulisentis missouriensis was determined by sampling at least 29 creek chubs, Semotilus atromaculatus, from Easly Creek, Richardson County, Nebraska, every month from February 1996 to March 1997. In general, mean abundance and prevalence of the acanthocephalans increased with the age or length of chubs. It is unlikely that this distribution is explained by increased consumption of intermediate hosts by older, larger fish or by predatory fish acquiring parasites from paratenic hosts. The intermediate host for P. missouriensis is the cyclopoid copepod Acanthocyclops robustus, and creek chubs do not consume more microscopic crustaceans as they age or grow. Instead, the percentage of fish in the diet of creek chubs increases. Furthermore, P. missouriensis apparently does not use paratenic hosts. In laboratory infections, P. missouriensis survived predation of its original definitive host and transferred to the predator. Postcyclically transmitted P. missouriensis survived at least 14 days in the intestine of creek chubs, where they localized around the first flexure beyond the stomach. All stages of development of both sexes were transferred successfully. Postcyclic transmission is a plausible explanation, in some cases, for the greater worm burden frequently observed in older, larger hosts and for the occurrence in top carnivores of parasites not known to have paratenic hosts. This method of transmission appears to result in distribution of acanthocephalans to groups of animals that otherwise would be inaccessible.

Differential phenoloxidase activity between native and invasive gammarids infected by local acanthocephalans: differential immunosuppression?

Manipulative endoparasites can alter the behaviour and the physiology of their intermediate hosts in ways that increase the probability of successful transmission to the final host. This requires that the parasite is able to circumvent its host's immune defence. Successful immune evasion may depend on host-parasite coevolutionary history and the appearance of new hosts invading the local host population may promote local parasite maladaptation. To test this hypothesis, we examined the effect of 2 acanthocephalan parasites, Pomphorhynchus laevis and Polymorphus minutus, on the immunity of their local and new invasive gammarid intermediate hosts, respectively Gammarus pulex and Gammarus roeseli. We found that infection by each parasite was correlated with a decrease, at different degrees, of the standing level of immune defence in local hosts--measured as the phenoloxidase (PO) enzyme activity--whereas invasive hosts infected by P. laevis had their PO-enzyme activity enhanced. These results suggest that these acanthocephalans evade their local host immune response through immunosuppression but cannot evade the immune response of their new invasive host. The potential role of this maladaptation on the success of invasive species is discussed.

Interspecific interactions between Acanthocephala in the intestine of brown trout: are they more frequent in Ireland?

The aim of this paper was to test the hypothesis that when the 2 species of Acanthocephalan Pomphorhynchus laevis and Acanthocephalus clavula are 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 for P. laevis in the presence of A. clavula in wild trout. Results from the niche width analysis also support the observations on average position in single and concurrent infections. The niche width of P. laevis when it co-occurred with A. clavula decreased markedly in high intensity infections compared to low intensity infections.

[Ultrastructure of the surface complex of acanthocephalans with the example of Filicollis anatis (Palaeacanthocephala: Polymorphidae) and Neoechinorhynchus crassus (Eoacanthocephala: Neoechinorhynchidae)]

Fine morphology of external tegument (surface complex) of young and mature acanthocephalans Filicollis anatis and young Neoechinorhynchus crassus is described. Based on comparative analysis of the obtained results and literature data, the surface complex of all examined acanthocephalans is shown to have principally similar structure at all stages of life cycle. Differences between species examined are found in quantitative characters only and they are related either to age or ecology of worms (embryonic larvae).

A comparative analysis of adult body size and its correlates in acanthocephalan parasites

Adult acanthocephalan body sizes vary interspecifically over more than two orders of magnitude; yet, despite its importance for our understanding of the coevolutionary links between hosts and parasites, this variation remains unexplained. Here, we used a comparative analysis to investigate how final adult sizes and relative increments in size following establishment in the definitive host are influenced by three potential determinants of acanthocephalan sizes: initial (cystacanth) size at infection, host body mass, and the thermal regime experienced during growth, i.e. whether the definitive host is an ectotherm or an endotherm. Relative growth from the cystacanth stage to the adult stage ranged from twofold to more than 10,000-fold across acanthocephalan species, averaging just over 100-fold. However, this relative increment in size did not correlate with host mass, and did not differ between acanthocephalan species using ectothermic hosts and those growing in endothermic hosts. In contrast, final acanthocephalan adult sizes correlated positively with host mass, and after correction for host mass, final adult sizes were higher in species parasitising endotherms than in those found in ectotherms. The relationship between host mass and acanthocephalan adult size practically disappears, however, once phylogenetic influences are taken into account. Positive relationships between adult acanthocephalan size, cystacanth size and egg size indicate that a given relative size is a feature of an acanthocephalan species at all stages of its life cycle. These relationships also suggest that adult size is to some extent determined by cystacanth size, and that the characteristics of the definitive host are not the sole determinants of parasite life history traits.

Effects of conspecifics and heterospecifics on individual worm mass in four helminth species parasitic in fish

Intraspecific and interspecific effects on the growth and body size of helminths are rarely studied in natural situations, yet knowing what determines helminth sizes and thus fecundity is crucial to our understanding of helminth ecology and epidemiology. The determinants of average individual worm mass were investigated in four common species of helminths parasitic in trout, Salmo trutta. In the acanthocephalan Echinorhynchus truttae, there was a negative relationship between the intensity of infection by conspecifics and average individual worm size. However, in the acanthocephalans Pomphorhynchus laevis and Acanthocephalus anguillae and in the cestode Cyathocephalus truncatus, the relationship was positive: individual worms were larger on average when co-occurring with many conspecifics than when co-occurring with very few. In addition, the average mass of individual C. truncatus in a host decreased as the total mass of other helminth species in the same host increased. This interspecific effect involves the whole helminth community, as the combined effect of all other helminth species is a better predictor of reduced mass in C. truncatus than the mass of any other species taken on its own. These results illustrate the importance of considering helminth interactions and helminth growth in a natural setting.

Activity levels and predator detection by amphipods infected with an acanthocephalan parasite, Pomphorhynchus laevis

The acanthocephalan parasite Pomphorhynchus laevis (Müller, 1776) uses freshwater amphipods as its intermediate host. In order to complete the life cycle, the infected amphipod must be consumed by a fish, where the acanthocephalan will mature and reproduce. Parasite transmission, and therefore fitness, could be enhanced if infected amphipods fail to detect or avoid predatory fish. We compared the activity levels of infected and non-infected amphipods, Echinogammarus stammeri (Karaman, 1931), in both the presence and absence of odours from its natural, definitive host, the fish Leuciscus cephalus (L.). Throughout the experiment, infected amphipods were more active than were non-infected individuals. The non-infected amphipods reduced their activity after the addition of fish odours, but the infected amphipods failed to show a significant decrease. The failure of infected amphipods to reduce activity levels in the presence of fish odour may reflect a parasite strategy to increase its chances of transmission by making its amphipod host more vulnerable to predation by fish.

Effect of cystacanth body size on adult success

Laboratory-reared cystacanths of Leptorhynchoides thecatus (Acanthocephala: Rhadinorhynchidae) were used to study the effect of cystacanth size on adult success and the factors that influence cystacanth size within the intermediate host. To assess how host size and intensity of infection influence cystacanth size, infected amphipods (Hyalella azteca) were measured, and sex, length, and width of cystacanths were determined. After a subset of cystacanths was measured, small- and large-size classes of cystacanths were designated. To determine how cystacanth size relates to adult size, green sunfish (Lepomis cyanellus) were fed 10 large or small cystacanths. Fish were dissected 6 wk after infection, and worms were removed. After adult worms were permanently mounted on slides, their length and width were measured. Intensity of infection and amphipod size significantly influenced cystacanth size in that large amphipods harbored larger cystacanths than did small amphipods and heavy infections produced smaller cystacanths than did light infections. Adult worms from the small and large cystacanth-size classes showed no significant difference in size; however, large cystacanths had a significantly higher establishment and survival than did small cystacanths: 40% of large worms and 14% of small worms were recovered. The results of this study indicate that host size and host sharing influence cystacanth size and that cystacanth size is an important factor in determining adult success.

Component population study of Acanthocephalus tumescens (Acanthocephala) in fishes from Lake Moreno, Argentina

Seasonal samples of all fish species from Lake Moreno were taken in order to determine the presence of paratenia, to evaluate the status of the hosts and to characterise the transmission of Acanthocephalus tumescens (von Linstow, 1896) at the component population level. Prevalence, mean abundance, mean intensity, numbers of gravid females, relative abundance of the different fish species, relative output of eggs and relative flow rates for each host species were computed. Acanthocephalus tumescens showed low host specificity, successfully parasitizing six out of eight fish species present in the lake. No paratenic infection was registered. If prevalence, mean abundance, and number of gravid females are considered, host species can be placed in a continuum from the most to least suitable as follows: Galaxias platei Steindachner, Diplomystes viedmensis (Mac Donagh), Oncorhynchus mykiss (Walbaum), Salvelinus fontinalis (Mitchill), Percichthys trucha (Cuvier et Valenciennes) and Galaxias maculatus (Jenyns). However, when parasite flow rates and egg output were calculated, including relative abundance of each fish species, the continuum was rearranged as follows: P. trucha, O. mykiss, G. platei / G. maculatus, S. fontinalis and D. viedmensis. The first four species would be the main contributors to the population of A. tumescens in this lake, P. trucha being the major one. Different regulatory and non-regulatory mechanisms are suggested.

Post-cyclic transmission in Acanthocephalus tumescens (Acanthocephala: Echinorhynchidae)

The aim of this study was to investigate the post-cyclic transmission of Acanthocephalus tumescens (von Linstow, 1896) from Galaxias maculatus Jenyns to Oncorhynchus mykiss (Walbaum). Wild G. maculatus naturally infected with A. tumescens were fed to cultured rainbow trout, which were sacrificed at the second, third and fourth weeks post infection. Normally attached male and female acanthocephalans were recovered alive from the intestine of rainbow trout. Parasites survive at least four weeks post infection, growing and attaining full sexual maturity. Prevalence and mean intensity generally decreased after infection. A. tumescens is the eighth acanthocephalan species in which post-cyclic transmission has been proven.

Helminth parasites of the southern sea otter Enhydra lutris nereis in central California: abundance, distribution and pathology

From October 1997 to May 2001, the gastrointestinal tracts from 162 beach-cast southern sea otters Enhydra lutris nereis were examined for helminth parasites and associated lesions. Carcasses were collected opportunistically in central California between Pt. San Pedro and Pt. Arguello. The primary goals of this study were to examine spatial and temporal variability in mortality due to parasite infection, identify factors associated with increased risk of infection, and illustrate the process of intestinal perforation by Profilicollis spp. Two genera and 4 species of acanthocephalans (Profilicollis altmani, P. kenti, P. major, Corynosoma enhydri) were found in 46.3% (Profilicollis spp.) and 94.4% (C. enhydri) of the carcasses examined. Three species of Digenea (Microphallus pirum, M. nicolli, Plenosoma minimum) were found in 47% of carcasses, at times in massive numbers (> 3000 per cm2). This is the first report of the latter 2 species from the sea otter. Mortality resulting from infection by Profilicollis spp. occurred in 13.0% (n = 21) of sampled carcasses, either directly, due to perforation of the intestinal wall and peritonitis (9.9%, n = 16), or indirectly, due to inhibition of host nutrient uptake or depletion of host energy reserves to fight chronic infections (3.1%, n = 5). The most massive infections (< 8760 parasites), and all cases of intestinal perforation occurred in carcasses infected by P. altmani and/or P. kenti. Mortality due to infection by Profilicollis spp. occurred more frequently among juvenile and old-adult females (chi2 = 17.479, df = 9, p = 0.045) from sand and mixed habitats in Monterey and Santa Cruz in the north of the sea otter range (chi2 = 9.84, df = 4, p = 0.045). Spatial differences in sea otter mortality coincided with the relative distributions of Profilicollis altmani, P. kenti, and P. major, and may reflect differences in sea otter diet, or differences in intensity of infection in intermediate hosts. Mortality rate due to infection by Profilicollis spp. decreased between 1998 and 2001, though differences were not significant (chi2 = 3.983, df = 3, p = 0.40), and may vary on multi-year cycles due to environmental factors such as density of definitive hosts (e.g. the surf scoter Melanitta perspicillata), or El Niño. Corynosoma enhydri did not cause significant damage to the intestine of the host, even when present in great numbers.

Effects of concurrent infections on Hymenolepis diminuta (Cestoda) and Moniliformis dubius (Acanthocephala). I. General effects and comparison with crowding. 1961

Hymenolepis diminuta developing in the presence of Moniliformis dubius are lighter, shorter, have a lower average weight:length ratio, and are limited to the posterior part of the intra-intestinal range they occupy in single infections. M. dubius in the concurrent infections are lighter, possibly shorter, have a lower average weight:length ratio, and tend to attach further anterior than in single infections. No effects were noted on the percent recovery of either helminth. Highly significant regressions of the wet weight, length, and weight:length ratio of H. diminuta and M. dubius on the number of larvae administered in single infections have been demonstrated. The weight and length of the H. diminuta, and the weight and weight:length ratios of the M. dubius, from concurrent infections were significantly lower than values predicted for single-species infections with a comparable number of worms. In crowded single-species infections, the distribution of attachment points of the H. diminuta is extended to include the anterior three-fourths of the intestine; in concurrent infections the tapeworms are limited to the posterior part of this range. Under crowded conditions, the M. dubius extend their linear intestinal distribution only slightly, all of the acanthocephalans attaching in the anterior half of the small intestine; in concurrent infections the acanthocephalans tend to be limited to the anterior part of this range. The distributional limitations in concurrent infections and the similarities between the effects of concurrent infection and crowding suggest that similar mechanisms, i.e., competition, possibly for carbohydrate, may be involved in the production of the effects of concurrent infection.

Intra- and interspecific density-dependent effects on growth in helminth parasites of the cormorant, Phalacrocorax carbo sinensis

The action of intra- and interspecific competition, mediated by density-dependent effects on growth, was investigated among the 3 helminth species found in the alimentary tract of 104 cormorants, Phalacrocorax carbo sinensis. Intraspecific density-dependent effects on worm sizes were observed in the abundant nematode Contracaecum rudolphii, as shown by a negative correlation between mean worm size and intensity of infection. Higher intensities of infection by C. rudolphii were also associated with more variable worm sizes in the nematode Syncuaria squamata, suggesting a one-sided and density-dependent interspecific effect. There was also clear evidence of some form of negative interaction between the nematode S. squamata and the acanthocephalan Southwellina hispida from two fronts. First, there was a strong negative correlation between the intensities of infection of the 2 species across hosts. Second, sizes of worms of 1 species became more variable as the number of worms of the other species per host increased, and vice versa. This interspecific density-dependent effect on growth was thus apparently symmetrical. We also found evidence that worm size is a predictor of egg output in the 3 helminth species, indicating that intra- and interspecific density-dependent effects on growth can affect population dynamics in these worms. These results illustrate the complex nature of density dependence in helminth growth, and how its effects can act both within and among species.

Acanthocephalans from crabs in the southeastern U.S., with the first intermediate hosts known for Arhythmorhynchus frassoni and Hexaglandula corynosoma

Cystacanths of Hexaglandula corynosoma were discovered in the fiddler crabs Uca spinicarpa and Uca rapax collected in Mississippi and Florida. Adults were present in yellow-crowned night herons, Nyctanassa violacea, collected in Florida. Cystacanths are very similar to adults, varying only in size and state of development. This is the first record of H. corynosoma from the United States and the first record of an intermediate host for any species of the genus. Cystacanths of Arhythmorhynchus frassoni were present in U. rapax from Florida. The proboscis size, shape, and armature of the cystacanths are identical to those of adults from clapper rails (Rallus longirostris) collected in several southeastern states. This is the first report of an intermediate host for A. frassoni. Profilicollis altmani cystacanths were collected from mole crabs (Emerita talpoida) at Atlantic Beach, North Carolina. These specimens, together with adults obtained from shore birds in Louisiana and Mississippi, are consistent with the view that P. altmani, Profilicollis kenti, and Profilicollis texensis are synonyms, with P. altmani having nomenclatural priority.

Patterns of intermediate host use and levels of association between two conflicting manipulative parasites

For many parasites with complex life cycles, manipulation of intermediate host phenotypes is often regarded as an adaptation to increase the probability of successful transmission. This phenomenon creates opportunities for either synergistic or conflicting interests between different parasite species sharing the same intermediate host. When more than one manipulative parasite infect the same intermediate host, but differ in their definitive host, selection should favour the establishment of a negative association between these manipulators. Both Polymorphus minutus and Pomphorhynchus laevis exploit the amphipod Gammarus pulex as intermediate host but differ markedly in their final host, a fish for P. laevis and a bird for P. minutus. The pattern of host use by these two conflicting manipulative parasites was studied. Their incidence and intensity of infection and their distribution among G. pulex were first examined by analysing three large samples of gammarids collected from the river Tille, Eastern France. Both parasites had low prevalence in the host population. However, temporal fluctuation in the level of parasitic infection was observed. Overall, prevalence of both parasite species was higher in male than in female G. pulex. We then assessed the degree of association between the two parasites among their intermediate hosts, using two different methods: a host-centred measure and a parasite-centred measure. Both measures gave similar results; showing random association between the two acanthocephalan species in their intermediate hosts. We discuss our results in relation to the selective forces and ecological constraints that may determine the pattern of association between conflicting manipulative parasites.

First description of an apical epidermis cone in Paratenuisentis ambiguus (Acanthocephala: Eoacanthocephala) and its phylogenetic implications

The proboscis apex of the eoacanthocephalan parasite Paratenuisentis ambiguus was studied, using electron and light microscopy, for a better understanding of the parasite's attachment at the intestinal wall of its definitive hosts (Anguilla rostrata and A. anguilla). The results suggest the presence of an epidermis cone with three nuclei at the proboscis apex of P. ambiguus instead of an apical sense organ, as has been previously supposed. Dendritic terminations, sensory nerves and secretory ducts were absent. The existence of many fibres suggests a mechanical function of the epidermis cone. Probably, it presses the proboscis apex and the anterior hooks into the intestinal wall of the definitive host. The presence of an epidermis cone in other eoacanthocephalan species can be derived from data in the literature. The absence of an epidermis cone outside the Eoacanthocephala suggests that it is an evolutionary innovation, supporting the monophyly of the Eoacanthocephala.

Corynosoma cetaceum in the stomach of franciscanas, Pontoporia blainvillei (Cetacea): an exceptional case of habitat selection by an acanthocephalan

Adult acanthocephalans are typically found in the intestine of vertebrates, where they can readily absorb nutrients. However, Corynosoma cetaceum has been frequently reported in the stomach of cetaceans from the Southern Hemisphere. The ecological significance of this habitat was investigated by examining data on number, sex ratio, maturity status, biomass, and fecundity of C. cetaceum in different parts of the digestive tract of 44 franciscanas Pontoporia blainvillei. Individual C. cetaceum occurred in the pyloric stomach (PS) and, to lesser degrees, in the duodenal ampulla (DA) and the main stomach (MS). Females outnumbered males in all chambers, although the sex ratio was closer to 1:1 in the MS; there also was a higher proportion of nongravid females, with a smaller biomass in the MS than in the PS and the DA. This evidence suggests that cystacanths are released from prey tissues in the MS, where entire prey are reduced to semi-fluid chyme. The 3 chambers harbored gravid females that did not differ significantly in mean biomass or fecundity. The maturity status of females was nearly identical between the PS and the DA. In the MS, the higher proportion of non-gravid females is probably due to the occurrence of newly recruited females to this site. Mean biomass and fecundity of gravid females covaried strongly and positively among chambers within hosts. These results suggest that there are no major differences between the 3 chambers with respect to the suitability for reproduction by C. cetaceum. However, although the MS is the largest chamber, it harbored the smallest number of gravid females. Interestingly, worms were largely restricted to the aboral portion of the MS, a sheltered region where a concentration of chyme, and thus nutrient availability, likely occurs. Linear distribution differences of gravid female C. cetaceum at increasing intensities suggest that reproductive females occupy chambers according to available space. In summary, the stomach should be considered the main habitat for C. cetaceum. The choice of this habitat is puzzling because other Corynosoma species occur in the intestine, and because the stomach of cetaceans is not an absorptive site.

Ultrastructure of the acanthella of Paratenuisentis ambiguus (Acanthocephala)

The fine structure of the early acanthella of Paratenuisentis ambiguus (Eoacanthocephala) was investigated. This developmental stage is characterised by losing its ability to move and by differentiation of adult structures. The frontal syncytium, present in the first developmental stage (the acanthor), is lost, while the epidermis and central syncytium persist. The epidermis of the acanthella contains a number of giant nuclei that are arranged into several small groups. The central syncytium is subdivided into different masses, containing nuclei that will give rise to the organs of the adult. The 'uncinogenous bands' extend into the anterior body of the acanthella. Formation of the hooks takes place within these strands. In all investigated stages no extracellular materials were observed. Posterior of the uncinogenous bands lies the brain anlage and the primordia of the reproductive system. Neither a sense organ nor a nervous system were found.

Seasonal population dynamics of Neoechinorhynchus qinghaiensis in the carp, Gymnocypris przewalskii przewalskii, from Qinghai Lake, China

Studies on the seasonal population dynamics of Neoechinorhynchus qinghaiensis (Acanthocephala: Neoechinorhynchidae) in its fish host Gymnocypris przewalskii przewalskii in the Qinghai Lake, China, were carried out with samples taken in May 1991, August 1992, November 1992 and February 1993. Prevalences were higher than 44% in all seasons. The mean intensity of infection was above 124 worms per fish. The maximum intensity of worms recovered from a single fish was 1402 in the autumn of 1992. Differences in the mean abundance, mean intensity and prevalence are not statistically significant relative to season and this is likely to be related to the stable temperatures recorded at the bottom of Qinghai Lake. Over-dispersed distributions of N. qinghaiensis in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of N. qinghaiensis showed males to be less than 3.5 mm and females between 0.5 and 4.25 mm, with the main recruitment phase in the worm populations occurring in the autumn, extending through winter and spring with the lowest recruitment occurring in the summer. The maturation and copulation of worms were mainly focused in the summer season. The sex ratio of female to male was both high in winter (1.51:1) and spring (1.48:1). The higher proportion of females and the change in the worm sex ratio in winter can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.

Host-parasite interactions in Acanthocephala: a morphological approach

In this review recent morphological and histochemical descriptions have been compiled of (mainly outer) features of all developmental stages of the Acanthocephala as well as what is known about the host's defence measures directed against these worms. From acanthors, for instance, it is documented how they escape melanization inside the haemocoel of a suitable intermediate host after they have been activated and released from their eggshell enclosure in the gut of the arthropod. Acanthors possess a complex set of eggshell-envelopes and interstices that fulfil different tasks. While the sequence of events inside the intermediate host's haemocoel is rather well known, what happens in paratenic hosts has been little studied. In final hosts the host-parasite interactions depend on the systematic affiliation of the parasite as well as the host and on the depth of penetration of each acanthocephalan species in the intestinal wall of the host. The mode of attachment also influences the microhabitat preference inside the gut. Mammals often reveal symptoms of high morbidity when infected with acanthocephalans, while fish seem to tolerate high intensities of worms deeply penetrating into their intestinal wall without showing pronounced symptoms of disease. The review also treats the subjects of host specificity, nutrient uptake and metabolism of the worms as well as their absorbance of metals and other elements. The high absorbance capacity for heavy metals suggests the usefulness of acanthocephalans as bioindicators.

Natural transfer of helminths of marine origin to freshwater fishes with observations on the development of Diphyllobothrium alascense

Infective stages of helminths of 5 species that occur as adults in marine mammals were found in burbot, Lota lota (L.) (Gadidae), from the lower Kuskokwim River (southwestern Alaska): Diphyllobothrium alascense Rausch et Williamson, 1958; Pyramicocephalus phocarum (Fabricius, 1780); Corynosoma strumosum (Rudolphi, 1801); Corynosoma semerme (Forsell, 1904); and Pseudoterranova decipiens (Krabbe, 1878). Some larval stages were obtained also from smelt, Osmerus mordax dentex Steindachner, an anadromous fish important as prey of burbot. Burbot, which are freshwater fish, could become paratenic hosts of those helminths by means of at least 3 interactions: by consuming marine fishes in brackish waters at river mouths, by feeding on marine fishes that enter lower reaches of rivers, or by preying on anadromous fishes as they migrate up rivers. Consumption of burbot by people may result in infection by helminths of marine origin; of those recorded, only P. decipiens may be significantly pathogenic. Attempts to rear P. phocarum in dogs were unsuccessful. Plerocercoids of D. alascense, of very small size and found only in the gastric lumen of burbot, readily infected dogs. For study of their development, strobilae were obtained at intervals of 48 hr to 32 days postinfection. In heavy infections, some strobilae developed slowly, while others underwent rapid development.

Sexual competition in an acanthocephalan parasite of fish

Acanthocephalans are polygamous parasites of vertebrates and some species are known to aggregate in sexual congress to mate. Such a reproductive behaviour could lead to male-male competition for access to females and could have consequences for sexual selection. We dissected 87 gobiid fish, Gobius bucchichii, harbouring 891 acanthocephalans, Acanthocephaloides propinquus. The parasites were sexed and their body sizes were measured. Testicular volume was also evaluated in 82 males in order to establish their phenotypic sexual investment in relation to the estimated sex ratio. We found that parasite intensity (i.e. the number of individuals/fish) was not correlated with fish size, but that parasite size was significantly related to host size. Our results showed that there was a significant relationship between the mean female body size and their number within one host. We found that when the percentage of male parasites in a host increased, presumably increasing male-male competition for access to females, males had a larger testicular volume. We discuss these results in terms of energy allocation, sexual and sperm competition. We conclude that competition for space should be less important for males than competition for access to females. Moreover, increasing testis size should confer advantages to males especially for their reproductive success when sperm competition occurs.

Effects of coinfection with Pomphorhynchus bulbocolli on development of leptorhynchoides thecatus (Acanthocephala) in amphipods (Hyalella azteca)

The effect of the presence of Pomphorhynchus bulbocolli on the development of Leptorhynchoides thecatus (Acanthocephala) in amphipod intermediate hosts (Hyalella azteca) was examined. Two groups of amphipods were exposed either to eggs of both species (experimental) or only to L. thecatus eggs (control). Amphipods of both groups were dissected 39 days postexposure. The percentage of L. thecatus at the cystacanth stage and mean abundance of cystacanths and precystacanths per amphipod were determined. Contingency table analysis and Fisher's exact tests demonstrated that a significantly smaller proportion of L. thecatus reached the cystacanth stage in coinfected amphipods of the experimental group than either worms in the control group or worms in L. thecatus-only infections of the experimental group. Interspecific interaction between acanthocephalans in intermediate hosts has not been reported previously. Coinfection reduces the number of L. thecatus in amphipods available for transmission to definitive hosts. Habitat separation by eggs of L. thecatus and P. bulbocolli might reduce this effect if amphipods are less likely to become coinfected when eggs are in different microhabitats than when they are not.

Uptake of lead by Pomphorhynchus laevis cystacanths in Gammarus pulex and immature worms in chub (Leuciscus cephalus)

The uptake of lead by cystacanths of the acanthocephalan Pomphorhynchus laevis in naturally infected amphipods, Gammarus pulex, and by immature parasites in experimentally infected fish, Leuciscus cephalus, was examined following 3-week experimental exposures (0.01 and 0.1 mg l(-1) Pb2+). Both G. pulex and the cystacanths of P. laevis accumulated lead but concentrations in the parasites were lower than in the host tissues at the low lead dose and significantly lower at the high dose. P. laevis from chub exposed to 0.01 mg l(-1) lead contained significantly more of the metal than the tissues of their host. Interestingly, there was an increase in the mean lead levels in the parasites from the control chubs which was concurrent with a decrease in host tissue concentrations. The results of this experimental study therefore confirm previous suggestions that heavy metals are predominantly accumulated by acanthocephalans inside the fish definitive host and not by cystacanths in the haemocoel of the amphipod intermediate host. The microhabitat of the parasite is therefore of primary importance rather than its developmental stage. Furthermore, metal concentrations in adult acanthocephalans will respond rapidly to changes in environmental exposure of their hosts.

The cement apparatus of larval and adult Pomphorhynchus laevis (Acanthocephala: Palaeacanthocephala)

Light and electron microscopy were used to study the ultrastructure of the cement apparatus, namely cement glands and cement ducts of mature specimens of the acanthocephalan parasite Pomphorhynchus laevis Müller, 1776, recovered from the digestive tracts of fish Leuciscus cephalus Risso, 1826. In addition, the cement glands of immature P. laevis found within the body cavity of the fish Alburnus alburnus alborella De Filippi, 1844 were examined. In a mature male of P. laevis the 6 cement glands are rounded to oval in shape and each of them has an outer cytoplasmic layer containing nuclei and surrounding a space for storage of the cement material within the gland. The nuclei have an irregular outline and the cytoplasm of the cells contains round, membrane-bound secretory granules approximately 1 micron in diameter. Nuclei surrounded by secretory granules were present inside the gland lumen. Within the gland ducts of mature males, granules were present within the wall thickness and, inside the luminal area, mitochondria were encountered. In contrast, within the cement glands of immature P. laevis there were no secretory granules and the chromatin of the nuclei appeared condensed. The nature of the secretory product of the cement glands was investigated with histological and electrophoretic methods. A protein with molecular weight of 23 kDa was recorded as a major component of cement.

Gastrointestinal helminths in the river otter (Lutra canadensis) in Tennessee

The first records of 3 helminth parasites from otters, Lutra canadensis, collected in Tennessee are reported. Digestive tracts of 91 river otters collected from 1983 to 1993 were examined for helminth parasites. Thirty otters were infected with Baschkirovitrema incrassatum, 5 otters were infected with Acanthocephalus sp., and 1 otter was infected with 2 Strongyloides lutrae. No significant differences in prevalence, mean abundance, or mean intensity of B. incrassatum occurred between counties or months. No significant differences in the prevalence or mean intensity of B. incrassatum occurred between years, but significant yearly differences in mean abundance were recorded from 1988 through 1993 (P < 0.05). There were no statistical differences in B. incrassatum parasitization between males and females or juvenile and adult otters.

Cyathocephalus truncatus (Cestoda: Spathebothridea) in its intermediate host Echinogammarus stammeri (Amphipoda) from the River Brenta, northern Italy

A study was carried out on the occurrence of the tapeworm Cyathocephalus truncatus (Pallas, 1781) (Cestoda: Spathebothridea) in its intermediate host, the amphipod Echinogammarus stammeri, in the River Brenta. A total of 18,860 E. stammeri was examined from July 1990 to June 1994; only 25 of them (prevalence 0.13%) were infected with tapeworm larvae (intensity of infection 1 larva/host). Co-occurrence of C. truncatus larvae with the larva of the acanthocephalan Pomphorhynchus laevis (Müller, 1776) was recorded in 15 amphipods. Tapeworms were localized in the anterior portion of each amphipod's hemocoel, in intimate contact with E. stammeri internal organs such as the alimentary canal, and frequently induced its displacement. No differences in integumental pigmentation were noticed between infected and non-infected amphipods, and some infected E. stammeri females were ovigerous.

Observations on the host specificity of Pomphorhynchus patagonicus (Acanthocephala) from the Alicura Reservoir (Patagonia, Argentina)

The acanthocephalan Pomphorhynchus patagonicus was found in 3 species of fish in the Alicura Reservoir (Patagonia, Argentina). These included Oncorhynchus mykiss, Patagonina hatcheri, and Percichthys trucha. Prevalence, intensity, size of the parasites, and percentage of gravid females were analyzed. The relatively low prevalence and intensity were probably due to the low consumption of the intermediate host, Hyalella patagonica. The highest values of intensity, length, and percentage of gravid females were found in Percichthys trucha. This species is considered to be the preferred host of P. patagonicus in the reservoir. No mature eggs were found in O. mykiss; this, together with the parasite's low growth rate, underlines the hypothesis that this species is not a suitable host for P. patagonicus.

Seasonal occurrence and maturation of Neoechinorhynchus rutili (Acanthocephala) in barbel, Barbus barbus (Pisces), of the Jihlava River, Czech Republic

From April 1992 until June 1993, the seasonal occurrence and maturation of the acanthocephalan Neoechinorhynchus rutili in its definitive host, the barbel (Barbus barbus), was studied in the Jihlava River (the Danube basin), Czech Republic. The parasite occurred in barbel throughout the year (overall prevalence 84% and intensity of infection 1-533 [mean 25] acanthocephalars per fish), but there were distinct seasonal fluctuations in prevalence and mean intensity values: prevalence attained 100% in February and March, whereas its lowest value was recorded in July; the lowest values of mean intensity occurred in July-August. Both prevalence and mean intensity values distinctly increased with the body length of hosts. The parasite exhibited a distinct annual maturation cycle when egg-producing females were present mainly in the spring and summer (May-July) and, at a lesser extent, also from December to April of the next year. The seasonal maturation of N. rutili appears to be induced principally by the temperature regimen in the locality. N. rutili cystacanths were recovered from larval Sialis lutaria (Megaloptera) (prevalence 6%).

Metabolism of long-chain fatty acids, alcohols and alkylglycerols in the fish parasite Paratenuisentis ambiguus (Acanthocephala)

Specific differences between the acyl composition of lipids of the helminth Paratenuisentis ambiguus and its host eel, as shown previously, prompted us to study the lipid metabolism in this intestinal fish parasite. Adults and larvae of P. ambiguus were fed various lipid precursors, e.g., fatty acids, long-chain alcohols and 1-O-alkylglycerols, which may occur as common nutrients of intestinal parasites. Incorporation of [1-14C]palmitic acid into neutral and polar lipids was found to be similar under aerobic and near-anaerobic conditions. In adult parasites maintained in culture medium supplemented with glucose, [1-14C]palmitic acid was incorporated mainly into triacylglycerols and phosphatidylcholines, whereas [1-14C]oleic acid was incorporated preferentially into triacylglycerols. In fasted adults, as well as in larvae, [1-14C]oleic acid was mainly transferred to phosphatidylcholines. Lipolytic activity was detected in adult parasites that had been incubated with radioactive trioleoylglycerol. [1-14C]Hexadecan-1-ol was oxidized in P. ambiguus at a high rate to labeled palmitic acid, which was incorporated into various lipid classes of P. ambiguus. Small but significant proportions of radioactivity from hexadecan-1-ol were incorporated into ether glycerolipids of the parasite. A more direct precursor in ether glycerolipid metabolism, i.e., rac-1-O-[1'-14C]hexadecylglycerol, was incorporated into alkyl and 1'-alkenyl moieties of choline and etha-nolamine ether-glycerophospholipids of P. ambiguus in high yield. High proportions of labeled diacylglycerols, triacylglycerols and steryl esters were detected in surface lipids as well as lipid extracts of the culture media after incubation of P. ambiguus with [1-14C]palmitic or [1-14C]oleic acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Establishment, survival, site selection and development of Leptorhynchoides thecatus in largemouth bass, Micropterus salmoides

Establishment, survival and distribution of Leptorhynchoides thecatus (Acanthocephala) were investigated in largemouth bass, Micropterus salmoides, fed 10, 25, or 40 cystacanths and examined at 1, 3 or 5 weeks post-infection. Worms established widely in the alimentary tracts of bass but by 5 weeks post-infection had localized in the pyloric caeca and intercaecal region. Other individuals moved to parenteral sites where they remained immature, though viable. In the 10- and 25-level exposures, establishment and survivorship in the alimentary tract were roughly proportional to the dose of cystacanths. After 1 week post-infection in the 40-level exposure class, numbers of worms in the alimentary tract decreased significantly and parenteral occurrence increased significantly. Total survival of L. thecatus appeared to be density-independent. Maturation of worms was retarded temporarily as intensity of infection increased, but by 5 weeks post-infection worms from all doses were at roughly the same stage of development within sex. The caeca and intercaecal area apparently did not differ in their suitability for maturation.