Diets of sympatric flatfishes, Hippoglossoides platessoides, Pleuronectes ferrugineus, Pleuronectes americanus, from Sable Island Bank, Canada

Prey exploitation was documented for Hippoglossoides platessoides, Pleuronectes ferrugineus , and P. americanus collected from southeast Sable Island Bank in February and June 1989. Diets varied significantly by sample and with fish species and length. Of 239 species consumed by flatfishes, 66 were determined to be principal prey. Crustaceans, particularly amphipods, were the most frequently exploited prey of all three flatfish species. Small H. platessoides fed on suprabenthic fauna, while larger fish exploited epifauna and hyperiid suprafauna. P. ferrugineus exploited epibenthic fauna, consuming crustaceans and tunicates when small and polychaetes when larger. P. americanus preyed on epifauna; smaller fish exploited polychaetes while larger fish usually consumed crustaceans associated with ectoproct colonies. Feeding intensity was dramatically lower in February, food being found in stomachs of only 36% of H. platessoides and 49% of P. ferrugineus , and lacking in the stomachs of P. americanus . In June, stomachs of 86% of H. platessoides , 94% of P. ferrugineus and 96% of P. americanus contained food. Results indicate that prey resources for the three flatfish species are partitioned by specific habitat and prey type preferences.     

Prevalence, intensity, and differential development of Pseudodelphis oligocotti (Nematoda: Dracunculoidea) in sympatric fish hosts of the northeastern Pacific coast

Counter to expectations of coevolved parasite-host relationships, parasites frequently infect hosts that never contribute to their reproduction, making the identification of a parasite's true host-specificity problematic. Pseudodelphis oligocotti (Nematoda: Dracunculoidea) infects several coastal Pacific fishes, but its course of development appears highly variable, suggesting that incidence does not reflect effective host range. To determine the host range of P. oligocotti and describe its relationship to various potential hosts, 24 fish species were examined from several British Columbia localities for prevalence, intensity, and extent and tissue location of parasite development. Pseudodelphis oligocotti infects 9 species of fishes from 5 orders, of which penpoint gunnel, Apodichthys flavidus, showed the highest prevalence and intensity, up to 80% and 19 (+/- 17.1 SD) worms per host, respectively. Although subadult and adult P. oligocotti occurred in all 9 fishes, larvigerous P. oligocotti only occurred in A. flavidus and rarely in the northern clingfish, Gobiesox maeandricus. Infective first-stage larvae were recovered from gill tissue of A. flavidus. Thus, at most only 2 of the 9 host species infected by P. oligocotti actually contribute to its transmission. The occurrence of P. oligocotti in diverse hosts may be accounted for by the parasite's indiscriminant mode of transmission via ingestion of free-living intermediate copepod hosts, where highly exposed or more suitable fishes (or both) are closely related by diet and microhabitat. This study demonstrates how parasite transmission and host ecology can greatly affect observed host range and ultimately its potential for expansion.     

Alimentary tract helminths of four pleuronectid flatfish in relation to host phylogeny and ecology

Eighteen species of helminths were analysed in relation to host–parasite specificity and the effect of host ecological preferences on the establishment of the parasite fauna in the alimentary tract of four pleuronectid flatfish, flounder Pleuronectes flesus , witch flounder Glyptocephalus cynoglossus , American plaice Hippoglossoides platessoides , and Atlantic halibut Hippoglossus hippoglossus in northern Norway. Thirteen species were generalists and the diversity of the parasite faunas decreased with increasing depths inhabited by the host. Similarities were greatest between the parasite faunas of flounder and American plaice and least between flounder and witch flounder. Host ecology, rather than phylogenetic relationships of these hosts, mainly influences the composition and diversity of the parasite communities of flatfishes in northern Norway.     

Effects of age, sex and abundance on the bathymetric pattern of American plaice in the southern Gulf of St Lawrence

American plaice Hippoglossoides platessoides density in September in the southern Gulf of St Lawrence was strongly related to depth, with peak densities at intermediate depths (70–90 m). Bathymetric pattern was similar for all ages of plaice (3–12 + year) and varied little among years. Densities were highest at similar depths for males and females, but depth distribution tended to be more spread out for females. Depth distribution was not significantly density dependent except for 10-and 11-year-old males and for females aged 12 years and older. In the three significant cases, depth distribution tended to spread out as abundance increased. Water temperature and depth were closely linked in the southern Gulf, but plaice depth preferences could not be attributed solely to temperature selection.     

Identification of the copepod intermediate host of the introduced broad fish tapeworm, Diphyllobothrium latum, in Southern Chile

The broad fish tapeworm, Diphyllobothrium latum, is an exotic species in both Chile and Argentina, and until now, its copepod host has remained unknown in South American waters. The objective of this study was to identify calanoid copepod species that may be intermediate hosts for D. latum in Lake Panguipulli, Chile. In this lake, the highest levels of infection by this tapeworm occur in the introduced rainbow trout, Oncorhynchus mykiss. Of the 2 calanoid copepods found in Lake Panguipulli, Diaptomus diabolicus and Boeckella gracilipes, only D. diabolicus became infected on experimental exposure to coracidia. Prevalence (mean intensity) of experimental infection in adult copepods was 73.2% (2.8 procercoids per host). Diaptomus diabolicus has been demonstrated to be a new intermediate host; this is the first record of a copepod host for D. latum in South America.     

Competitive Growth Strategies in Intermediate Hosts: Experimental Tests of a Parasite life-History Model Using the Cestode, Schistocephalus solidus

In parasites with a complex life cycle, the fitness of an individual depends on its probability of reaching the final host and on its fecundity. Because larval growth in intermediate hosts may affect both transmission and adult size, selection should optimize growth patterns that are conditional on the presence and number of conspecific competitors. A recent model predicts that the total parasite volume per host should increase with intensity if larvae are able to vary growth depending on the number of conspecifics in the host (Life History Strategy hypothesis, i.e. LHS). Further, we would here expect growth rates to increase with intensity. By contrast, under the simplest alternative hypothesis of Resource Constraints (i.e. RC), the total parasite volume should remain constant. We experimentally infected copepods Macrocyclops albidus with the cestode Schistocephalus solidus to achieve 1, 2 or 3 parasites per host taking care that hosts had similar quality status at each infection level, and compared larval growth trajectories at the three intensity levels. The asymptotic total parasite volume was larger in double and triple infections than in single infections. Furthermore, the asymptotic total parasite volume was significantly larger in triple than in double infections but only in larger copepods that were less constrained by a host-size ceiling effect. These results, together with the fact that growth rates increased with intensity, support the LHS hypothesis: procercoids of a tapeworm may “count” their conspecific competitors in their first intermediate host to harvest its resources strategically until the next step in their complex life cycle. Co-ordinating editor: A. Biere     

Parasite‐induced Changes in the Anti‐predator Behavior of a Cricket Intermediate Host

Many parasites with complex life cycles are known to modify their host phenotype to enhance transmission from the intermediate host to the definitive host. Several earlier studies explored these effects in acanthocephalan and trematode parasites, especially in aquatic ecosystems; however, much less is known about parasite‐mediated alterations of host behavior in terrestrial systems involving nematodes. Here, we address this gap by investigating a trophically transmitted nematode (Pterygodermatites peromysci) that uses a camel cricket (Ceuthophilus pallidipes) as the intermediate host before transmission to the final host, the white‐footed mouse (Peromyscus leucopus). In a laboratory experiment, we quantified the anti‐predatory responses of the cricket intermediate host using simulated predator cues. Results showed a decrease in jumping performance among infected crickets as compared with uninfected crickets, specifically in terms of frequency of jumps and jumping distance. Additionally, the relationship between parasite load and frequency of jumps is negatively correlated with the intensity of infection. These behavioral modifications are likely to increase vulnerability to predation by the definitive host. An analysis of the age‐intensity pattern of infection in natural cricket populations appears to support this hypothesis: parasites accumulate with age, peak at an intermediate age class before the intensity of infection decreases in older age groups. We suggest that older, heavily infected crickets are preferentially removed from the population by predators because of increased vulnerability. These results show that cricket intermediate hosts infected with P. peromysci have diminished jumping performance, which is likely to impair their anti‐predatory behavior and potentially facilitate parasite transmission.     

Fitness of indirectly transmitted pathogens: restraint and constraint

Many pathogens of medical and veterinary importance have obligatory multihost life cycles. Yet, theoretical models aiming to predict patterns of pathogen reproductive success and the limited empirical data available with which to evaluate them, focus on directly transmitted microparasites. Patterns of host exploitation and the relative fitness of individual pathogen genotypes throughout the different host stages of multihost life cycles have thus remained ignored. We examined correlated responses to artificial selection of Schistosoma mansoni lines selected for high or low infection intensity in the intermediate host. Pathogen fitness in the intermediate host was strongly inversely correlated with pathogen fitness in the definitive host. Moreover, high pathogen infection intensity was associated with decreased, rather than increased, virulence to its intermediate host. These results raise important implications regarding the impact of genetic constraints on the maintenance of genetic and phenotypic polymorphisms in natural populations, the evolution and coevolution of parasite virulence and host specialization, as well as the success of host-directed control programs.     

The role of Cytograpsus angulatus (Crustacea; Brachyura) in the life cycles of Microphallus szidati (Digenea; Microphallidae) and Falsifilicollis chasmagnathi (Acanthocephala; Filicollidae): various aspects of their ecological parasitology

Based on a study of the larvae from two helminth species parasitizing the crab Cyrtograpsus angulatus Dana, 1851 (Microphallus szidati Martorelli, 1986 and Falsifilicollis chasmagnathi Holcman-Spector et al., 1977), from Mar chiquita lagoom (Argentina) together with the analyses of their life cycles and rates of prevalence, intensity and association coefficient (compared in definitive and intermediate host) the following conclusions have been reached: a) C. angulatus suns to be an excellent intermediate host in the life-cycles of the studied helminths; b) the size of the crabs and the occurrence of natural amputations in the females (Spivak & Politis, in press) appeared correlated with prevalence; c) in the studied crabs the prevalence for F. chasmagnathi is higher in males than in females; d) the intensity did not appear correlated with size and sex of the intermediate host; e) M. szidati and F. chasmagnathi are closely associated with the intermediate host; f) C. angulatus and Himantopus melanurus Vieillot, 1817 (Aves; Recurvirostridae) are reported as new intermediate and definitive hosts, respectively, for F. chasmagnathi; g) Chasmagnathus granulata Dana, 1851 (Crustacea; Brachyura) is reported as a new intermediate host for M. szidati.     

Occurrence and maturation of Rhabdochona gnedini (Nematoda: Rhabdochonidae) in the barbels of the Sousa River, Portugal

Data on the seasonal occurrence and maturation of Rhabdochona gnedini Skrjabin, 1946 in its definitive host, the barbel Barbus bocagei, from the Sousa River, in northern Portugal, are presented. Monthly samples were taken from November, 1998 to October, 1999. A total of 178 fish specimens were inspected. R. gnedini occurred with high prevalences during whole year, attaining the highest values of intensity in summer (overall prevalence and mean intensity 85% and 31, respectively). A clear annual cycle of maturation was observed; females with mature eggs occurred in spring and summer. Unidentified Rhabdochona larvae were recorded from the trichopteran larvae Hydropsyche sp. (prevalence and intensity 29% and one to 34, respectively). These larvae are presumptive intermediate host for R. gnedini.     

Field evidence of host size-dependent parasitism in two manipulative parasites

The distribution of parasites within host natural populations has often been found to be host age-dependent. Host mortality induced by parasites is the commonest hypothesis proposed for explaining this pattern. Despite its potential importance in ecology, the parasitism intensity in relation with the host age has rarely been studied in the field. The 2 manipulative acanthocephalans, Polymorphus minutus and Pomphorhynchus laevis, use the amphipod Gammarus pulex as an intermediate host, and their infection intensity and incidence among G. pulex populations were examined by analyzing 2 large samples of hosts collected in eastern France. Both parasites had low prevalence in the host populations, but their mean abundances were highly related with gammarid age. For the 2 acanthocephalans, results reported a disappearance or an absence of heavily infected hosts in the older host age classes. These results suggested that parasites that alter intermediate host behavior for enhancing their transmission success to the definitive host reduce the survival of their intermediate host. In conclusion, manipulative parasites might act as a mechanism regulating the density of gammarid populations.     

Prevalence and intensity of Angiostrongylus cantonensis in freshwater snails in relation to some ecological and biological factors

The purpose of the study was to record different intermediate hosts of A. cantonensis and to determine the infection prevalence and intensity of this parasite in freshwater snails in relation to some ecological and biological factors. The study was conducted at Al-Salam irrigation Canal and Al-Abtal village (north Sinai) for one year, from March 2004 to February 2005. Thirteen species of freshwater snails of nine families were examined for A. cantonensis infection. Six species were found infected with A. cantonensis larvae. These species were L. carinatus, C. bulimoides, C. cyclostomoides, B. alexandrina, L. natalensis and M. tuberculta. The infection prevalence of A. cantonensis in the examined snails ranged from 0.63 to 2.24%. L. carinatus snail had the highest prevalence, mean abundance and mean intensity of A. cantonensis infection. Positive correlations were found between both prevalence and mean abundance of A. cantonensis and host size in L. carinatus and M. tuberculata. Negative correlations were detected between salinity and prevalence, mean abundance and mean intensity of larvae of A. cantonensis. The results demonstrated seasonal and spatial variation in the prevalence, mean abundance and mean intensity of infection among examined snails. In this study, A. cantonensis larvae were found in a wide range of freshwater snails and M. tuberculata snail was recorded as a new intermediate host for the first time. In conclusion, further investigations in other areas and controlled laboratory experiments of infection approaches are required to evaluate the possible threat of this parasite on humans.     

The effects of parasite age and intensity on variability in acanthocephalan-induced behavioural manipulation

Numerous parasites with complex life cycles are able to manipulate the behaviour of their intermediate host in a way that increases their trophic transmission to the definitive host. Pomphorhynchus laevis, an acanthocephalan parasite, is known to reverse the phototactic behaviour of its amphipod intermediate host, Gammarus pulex, leading to an increased predation by fish hosts. However, levels of behavioural manipulation exhibited by naturally-infected gammarids are extremely variable, with some individuals being strongly manipulated whilst others are almost not affected by infection. To investigate parasite age and parasite intensity as potential sources of this variation, we carried out controlled experimental infections on gammarids using parasites from two different populations. We first determined that parasite intensity increased with exposure dose, but found no relationship between infection and host mortality. Repeated measures confirmed that the parasite alters host behaviour only when it reaches the cystacanth stage which is infective for the definitive host. They also revealed, we believe for the first time, that the older the cystacanth, the more it manipulates its host. The age of the parasite is therefore a major source of variation in parasite manipulation. The number of parasites within a host was also a source of variation. Manipulation was higher in hosts infected by two parasites than in singly infected ones, but above this intensity, manipulation did not increase. Since the development time of the parasite was also different according to parasite intensity (it was longer in doubly infected hosts than in singly infected ones, but did not increase more in multi-infected hosts), individual parasite fitness could depend on the compromise between development time and manipulation efficiency. Finally, the two parasite populations tested induced slightly different degrees of behavioural manipulation.     

Host phenology,geographic range size and regional occurrence explain interspecific variation in damselfly–water mite associations

In this study, we tested which host species’ characteristics explain the nature and level of parasitism for host damselfly (Coenagrionidae)–water mite (Arrenuridae) parasite associations. Prevalence and intensity of mite parasites, and mite species richness were examined in relation to geographic range size, regional occurrence, relative local abundance, phenology and body size of host damselfly species. A total of 7107 damselfly individuals were collected representing 16 species from 13 sites in southeastern Ontario and southwestern Quebec, Canada. Using comparative methods, differences in prevalence and intensity of parasitism could be predicted by a host species’ geographic range and phenology. Barcoding based on Cytochrome Oxidase I revealed 15 operational taxonomic units (OTUs) for mite species. The number of mite OTUs known to infest a given host species was explained by a host species’ regional occurrence. Our findings demonstrate the need to measure factors at several ecological scales in order to understand the breadth of evolutionary interactions with host–parasite associations and the selective ‘milieu’ for particular species of both hosts and parasites.     

First record of ostracods as natural intermediate hosts of Anguillicola crassus, a pathogenic swimbladder parasite of eels Anguilla spp

The ostracod Physocypria nipponica (Ostracoda: Candonidae) was found (prevalence 14.2%) to be the only intermediate host of the nematode Anguillicola crassus (Nematoda: Anguillicolidae), a pathogenic swimbladder parasite of eels, in a greenhouse-heated culture pond at Isshiki, Aichi Prefecture, Japan. Japanese eels Anguilla japonica from the same pond were found to be infected by adult A. crassus (prevalence 71.8%, intensity 1 to 6). This indicates that A. crassus could complete its life cycle under conditions of modern eel-culture technology where copepods were absent due to the unfavorable water quality for them, by utilizing ostracods as the intermediate host.     

High intensity and prevalence of two species of trematode metacercariae in the fathead minnow (Pimephales promelas) with no compromise of minnow anti-predator competence

Opportunity for parasites to manipulate host behavioral phenotype may be influenced by several factors, including the host ecology and the presence of cohabiting parasites in the same host. Metacercariae of Ornithodiplostomum ptychocheilus and "black spot" Crassiphiala bulboglossa have similar life cycles. Each parasite uses a littoral snail as a first intermediate host, fathead minnows as a second intermediate host, and a piscivorous bird as a final host. Metacercariae of black spot encyst in the dermal and epidermal tissues, while metacercariae of O. ptychocheilus encyst on the brain over a region that coordinates optomotor responses. Because of site differences within the host, we predicted that O. ptychocheilus metacercariae might manipulate the behavioral phenotype of minnows to facilitate transmission to the final host, but metacercariae of black spot would not. In our study population, prevalence was 100% for O. ptychocheilus , with an overall median intensity of 105 metacercariae per minnow. Prevalence of black spot was 60%, with a median abundance and intensity of 12 and 20 metacercariae per minnow for the overall sample and for infected fish, respectively. Minnows accumulated both parasites over time, producing significant correlations between intensity and minnow body length and between intensities of the 2 parasites. Minnows infected with black spot had on average twice as many O. ptychocheilus metacercariae as similar-sized minnows without any black spot cercariae. We found no correlation between body condition of minnows and intensity for either parasite. We measured 2 aspects of anti-predator competence to test for effects linked to parasite intensity. We found no correlation between intensity of either species of parasite and latency to behavioral response to attack from a mechanical model heron, nor was there any effect of parasite intensity on a measure of shoaling affinity. The absence of any detectable effect of metacercariae on anti-predator competence in minnows may reflect selection against parasite pathology from predation by non-hosts of the parasites and overwinter mortality due to low dissolved oxygen.     

Prevalence and intensity of Haemobaphes diceraus (Copepoda: Pennellidae) from shiner perch,Cymatogaster aggregata (Embiotocidae)

The prevalence and intensity of the hematophagous pennellid copepod Haemobaphes diceraus were monitored over a 10-mo period in shiner perch Cymatogaster aggregata at Pipers Lagoon, Nanaimo, British Columbia. The prevalence and mean intensity of metamorphosed adult female H. diceraus (n = 421) were 10.0% and 1.2 (+/-0.5 SD), respectively. The majority (97.9%) of infected fish had single infections, reflecting the possibility of intensity-dependent parasite-induced mortality, rejection of additional parasites, or both. Transforming females were detected throughout the year; however, there was no detectable seasonal pattern of colonization. Neither copepodids nor adult males of H. diceraus were observed on the gills of shiner perch, and this was consistent with the hypothesis that an intermediate host harbors these stages. Males of Haemobaphes sp. infected the gills of bay pipefish Syngnathus griseolineatus with a prevalence and mean intensity of 56.0% and 6.8 +/- 3.7, respectively. Transmission of H. diceraus to shiner perch probably occurs in inshore protected areas, where shiner perch ecologically overlap with the probable intermediate host of H. diceraus, the bay pipefish.     

Optimal growth strategies of larval helminths in their intermediate hosts

We consider optimal growth of larval stages in complex parasite life cycles where there is no constraint because of host immune responses. Our model predicts an individual's asymptotic size in its intermediate host, with and without competition from conspecific larvae. We match observed variations in larval growth patterns in pseudophyllid cestodes with theoretical predictions of our model. If survival of the host is vital for transmission, larvae should reduce asymptotic size as intensity increases, to avoid killing the host. The life history strategy (LHS) model predicts a size reduction <1/intensity, thus increasing the parasite burden on the host. We discuss whether body size of competing parasites is an evolved LHS or simply reflects resource constraints (RC) on growth fixed by the host, leading to a constant total burden with intensity. Growth under competition appears comparable with "the tragedy of the commons", much analysed in social sciences. Our LHS prediction suggests that evolution generates a solution that seems cooperative but is actually selfish.     

Effects of atrazine on cercarial longevity, activity, and infectivity

Susceptibility of free-living infective stages of parasites to contaminants is relatively understudied compared with independent effects on measures of host health or immunity, but may be important in affecting prevalence and intensity of parasite infections. We investigated whether atrazine, an herbicide commonly used in North America, affected the cercariae of 4 different species of digenetic trematodes, and found that effects of atrazine concentration on mortality and activity of cercariae varied among species. Mortality of Echinostoma trivolvis increased in a 200 microg/L atrazine solution, and a species of Alaria showed both decreased activity and increased mortality. We also examined whether the ability of E. trivolvis to infect the second intermediate host, larval amphibians, was compromised by atrazine exposure. Longevity and prevalence of E. trivolvis cercariae was affected at 200 microg/L atrazine, whereas intensity of infection in Rana clamitans tadpoles was reduced at both 20 microg/L and 200 microg/L atrazine. Our results indicate that the viability of cercariae of some species is compromised by exposure to atrazine, emphasizing the importance of considering the influence of contaminants on free-living stages of parasites in addressing how environmental degradation may relate to host parasitism.     

Larval morphology, genetic divergence, and contrasting levels of host manipulation between forms of Pomphorhynchus laevis (Acanthocephala)

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.