Similarity in parasite community structure may be used to trace latitudinal migrations of Odontesthes smitti along Argentinean coasts

The aims of this study were to determine the existence of migratory movements and to identify ecological stocks of the silverside Odontesthes smitti along its distribution in the Southern Atlantic Ocean, using metazoan parasites as biological tags. Samples were obtained from San José Gulf (SJ) (42° 25' S; 64° 07' W) and Nuevo Gulf (NG) (42° 47' S; 65° 02' W) in north Patagonia during winter and summer and in waters off Mar del Plata (MDP) (38° 03' S; 57° 32' W), Bonaerense region, during winter. Fifteen parasite species were collected. Multivariate statistical procedures on parasite community data showed strong effect of host size on the structure of parasite assemblages. Taking into account the variations among samples due to host size, the differential structure of parasite communities between SJ and NG suggests that fish inhabiting these localities could belong to different ecological stocks. Fish from MDP and SJ caught in summer showed similar composition in their parasite assemblages, which is congruent with a migratory cycle that implies that fish caught in MDP during winter inhabit SJ during summer. Further evidence of the Patagonian origin of MDP O. smitti is the presence of the digenean Proctotrema bartolii in fish from both regions. Proctotrema bartolii is acquired by O. smitti only in the Magellanic province, where its intermediate host, Darina solenoides, is distributed. The analyses suggest that O. smitti inhabiting north Patagonian gulfs could belong to different ecological stocks and that O. smitti caught in MDP could have come from SJ.     

Parasites of Argentine anchovy in the south-west Atlantic: latitudinal patterns and their use for discrimination of host populations

Four stocks of Argentine anchovy Engraulis anchoita in the south-west Atlantic, south of 34°S were identified by the use of parasites as biological tags. A total of 671 fish were examined for parasites and 19 parasite species were found in 664 Argentine anchovies. The parasite populations and both infra- and component communities showed marked latitudinal gradients. Cluster analyses allowed the identification of four groups, one composed of autumn samples (35–37°S) and three of spring ones. Among the latter, a Patagonian group (43–46°S) was clearly separated from a Bonaerense group, which was divided into two groups: North Bonaerense (34–40°S) and South Bonaerense (40–43°S). Autumn samples were characterized by low values of prevalence for most parasite species. Among spring samples Pseudanthocotyloides heterocotyle , Lecithochirium microstomum , Parahemiurus merus , Scolex polymorphus and Corynosoma australe were characteristic of the northern region, whereas Cardiocephaloides sp., Anisakis simplex , Contracaecum sp. and Hysterothylacium aduncum were more prevalent in southern waters. Latitudinal environmental gradients and their influence on the distribution of both zooplankton and definitive hosts, could be determinants of the clines observed.     

Parasites of Cynoscion guatucupa along South American Atlantic coasts: evidence for stock discrimination

Two stocks of striped weakfish Cynoscion guatucupa in the south‐west Atlantic Ocean, were identified using parasites as biological tags. A total of 297 fish caught in Brazil, Uruguay and Argentina, contained 29 species of metazoan parasites. Univariate analysis on parasite populations, as well as multivariate discriminant analysis, calculated for juvenile and adult fish separately, allowed the identification of the two stocks, one from Argentina and Uruguay and the other from Brazil, to be made. Southern samples were characterized by higher prevalences and abundance of larval endohelminths, whereas in the northern stock, gastrointestinal and ectoparasitic species were common. Discriminant analyses on parasite infracommunities of Brazilian fish showed notable differences between juvenile and adult hosts; no such trend was observed in fish from Argentina and Uruguay, despite differences between juveniles and adults at the population level. Different oceanographic conditions and their influence on the distribution of parasites as well as of other hosts involved in their life cycles could be key factors for the differences observed among stocks of C. guatucupa .     

Parasites as fish population tags and pseudoreplication problems: the case of striped red mullet Mullus surmuletus in the Spanish Mediterranean

Studies of parasites as fish population tags often apply a single round of sampling to identify potential stocks or predict harvest localities. However, the lack of replication generates pseudoreplication, implicitly assuming that infection levels are more similar between samples from the same locality than between samples from different localities. We evaluated this assumption in the case of the striped red mullet Mullus surmuletus in three localities of the Spanish Mediterranean separated by c. 300 km. Samples of 25 fish of similar size were collected in each locality in the summer and autumn of two consecutive years. Prevalence and abundance of three long-lived parasite taxa differed significantly among localities, indicating their potential as stock indicators. However, a cluster analysis (for prevalence) and a MANOVA (for abundance) indicated strong inter-sample variability, even within the same locality, with poor spatial segregation among samples. A linear discriminant analysis (LDA) based on the abundance of 17 parasite taxa correctly assigned over 80% of fish to their locality, and 95% bootstrap confidence intervals of percent classified fish per locality were narrow, indicating good and stable predictive power. However, when a LDA based on data from the first year was used to predict the locality of fish from the second year, predictive power dropped drastically (46% of correct allocation). Overall, we interpret that parasite communities of mullets change at a much lower spatial scale than that adopted in this study. This finding strongly suggests the need for proper replication to make reliable inferences about stock structure in fish populations based on parasitological data.     

Variations in the parasite fauna of the Patagonian toothfish (Dissostichus eleginoides Smitt, 1898), with length, season, and depth of habitat around the Falkland Islands

The parasite fauna of Dissostichus eleginoides was examined from locations around the Falkland Islands. In total, of 11,362 individual parasites of 27 taxa were recovered from 105 fish. Two species, Ceratomyxa dissostichi and Sphaerospora dissostichi, represent new host records. The nematode Ascarophis nototheniae and the larval acanothocephalan Corynosoma bullosum were found to be new locality records and add to the knowledge of the biogeography and host specificity of parasites on the Patagonian Shelf. There were no significant differences in the mean abundance and prevalence of parasites recovered between sexes. Therefore, sex was not considered in further analysis and the data were pooled. Cysts of unknown etiology (CUE), the monogenean Neopavlovskioides georgianus, the larval acanthocephalan Corynosoma bullosum, and the digenean Neolepidapedon magnatestis had significant positive correlations with increasing host length. The larval Trypanorhynch cestode Grillotia erinaceus and the digenean Elytrophalloides oatesi showed significant negative correlations with increasing host length. CUEs, N. georgianus, the digenean Gonocerca physidis and E. oatesi showed statistically significant prevalence between summer, winter, and spring. The effect of depth on parasite communities was also examined, initially using a linear discriminant function analysis. The prevalence of individual parasites was then compared between depth strata using the chi-square test. The parasite communities on the shelf and deep water (> 1,000 m) were found to be different, whereas those caught at intermediate depths on the shelf slope were found to have parasite communities that were intermediate, containing a mixture of shelf and deeper-water parasites. The causes of the variations in parasite faunas in association with these intrinsic and extrinsic factors are discussed.     

Populations and assemblages of parasites in hake, Merluccius gayi, from the southeastern Pacific Ocean: stock implications

To assess fish stocks, the populations and community assemblages of metazoan parasites were compared in 1172 Chilean hake Merluccius gayi landed at two major ports, and caught during 1991–1992 in three major fishing areas off central Chile. At least two ecological stocks are suggested, based on consistent differences in parasitism between body length classes for Grillotia dollfusi, Hysterothylacium sp., Clestobothrium crassiceps and Aporocotyle wilhelmi . More use should be made of the information on whole parasite assemblages including, for example, patterns of co-occurrence of parasite species. Univariate analyses on selected taxa in samples from different areas may show no differences because of the same prevalence or abundance for each parasite taxon, but opposite numerical arrangements of co-occurring taxa in community assemblages would remain undetected.     

Geographical patterns of parasite infracommunities in the rough scad, Trachurus lathami Nichols, in the Southwestern Atlantic ocean

We assessed temporal variability in parasite infections of rough scad (Trachurus lathami) in 3 samples from Miramar (MI) in 2008, separated by periods of 1 mo, and 2 samples from Villa Gesell (VG), 1 each in 2008 and 2009 (Buenos Aires Province, Argentina), respectively. A sample was also obtained from Cabo Frio (CF) (Brazil) in 2009 to compare differences in parasite communities between fish from this locality and each Argentinean locality. All rough scad were parasitized by at least 1 of 27 parasite species. Similarity-based multivariate analysis revealed significant differences between localities, but temporal homogeneity in each Argentinean locality. Overall, prevalence and abundance of parasite species were most similar between samples from MI and VG, while the greatest differences occurred between samples from MI and CF. A canonical analysis of principal coordinates showed significant differences among samples. Grillotia carvajalregorum was the most important species in determining the position of Argentinean samples, especially those from MI, while Ectenurus virgulus , Raphidascaris sp., and Hysterothylacium sp. were the most important species related to fish from CF. The parasite assemblage of T. lathami showed a notable temporal persistence within the same locality and a high variability at the spatial scale, suggesting the existence of 3 independent stocks of T. lathami in South Atlantic waters.     

Parasites as biological tags for stock discrimination of the Brazilian flathead Percophis brasiliensis in the south-west Atlantic

Three stocks of the Brazilian flathead Percophis brasiliensis were identified on the coast of Argentina and Uruguay using parasites as biological tags. A total of 177 fish were examined and 23 parasite species were found. Fish were caught in four zones: north of the Argentine–Uruguayan Common Fishing Zone (34°30′–36°30′ S; 53°30′–56°00′ W), south of the Argentine–Uruguayan Common Fishing Zone (38°08′ S 57°32′ W), El Rincón zone (39–41° S; 60–62° W) and San Matías Gulf (41°40′–42°10′ S; 63°50′–65°00′ W). Discriminant analyses allowed the identification of three discrete stocks in the four zones (86·44% of classified samples were correctly identified), with P. brasiliensis from both north and south of the Argentine–Uruguayan Common Fishing Zone clumping together, as a single stock. Some species were important in discriminating among groups, Anisakis simplex was related to southern areas, while Grillotia sp., Corynosoma australe and Hysterothylacium sp. were important in determining the position of fish from the Argentine–Uruguayan Common Fishing Zone. These results were corroborated by comparing parasite prevalence and abundance among zones. The main differences were observed in those comparisons involving fish from the San Matías Gulf. Fish from the Argentine–Uruguayan Common Fishing Zone were characterized by higher infections of Grillotia sp., C. australe, Corynosoma cetaceum and Hysterothylacium sp., while the samples from El Rincón and San Matías Gulf showed higher infections of A. simplex. Samples from San Matías Gulf were characterized by lower levels of parasitism for all other species. Differences in environmental factors and their influence on the distribution of zooplankton and other hosts in the food web may be differentially shaping the parasite community structure in each zone, resulting in identifiable stocks of the P. brasiliensis. The present study confirmed the existence of regional biological tags that delineated fish assemblages.     

Dispersion patterns of parasites in 0+ year three-spined sticklebacks: a cross population comparison

Two ciliates and 16 metazoan parasites were identified in 434 0+ year three-spined sticklebacks Gasterosteus aculeatus collected from two small rivers and four lakes located in Schleswig-Holstein, Germany. By repeated sampling and analysis of dispersion patterns of six frequently occurring parasites no consistent evidence was found for mortality induced by a single parasite species. Linear log-variance to log-mean abundance ratios with slopes of c. 2 indicated negative binomial distributions for five of the six parasites. The numbers of these six parasites were combined as multiples of S.D. of each parasite species over all samples to form an 'individual parasitation index' ( I _PI), which showed that only in one locality a slight decrease in parasite burden occurred between September and April. In two of the lake populations, however, there was a distinct decline in the degree of dispersion in spring samples. This indicates that a combination of different species might cause parasite-induced host mortality, undetectable by patterns obtained from single species. There were differences in parasite diversity and intensity of infection among river compared to lake populations suggesting a role for parasites as selective agents in the ecological divergence of three-spined sticklebacks.     

Notes on the biology of the Patagonian hake, Merluccius hubbsi (Marini), the southern blue whiting, Micromesistius australis (Norman) and others in the Falkland Islands shelf area

From the examination of samples of fish caught in two commercial surveys on trawling grounds around the Falkland Islands, it is noted that Patagonian hake, Merluccius hubbsi , southern blue whiting, Micromesistius australis , and others occurred in fishable quantities especially to the east of Beauchêne Islands where fishes were larger and more numerous. However 47% of the total catch consisted of southern blue whiting which was 100% infested by a myxosporidian parasite in its musculature rendering it unsuitable for human consumption.     

Resistance to abomasal nematodes and individual genetic variability in reindeer

Resistance to parasites is believed to have a widespread influence on demographic and adaptive processes. In systems where parasites impose a fitness cost on their host, heterozygotes may be selected because they are more resistant to parasites than homozygotes. Our objective was to assess the relationships between genomewide individual heterozygosity and abomasal nematode burdens in female Svalbard reindeer (Rangifer tarandus platyrhynchus) after the effects of host age, locality, season, and year had been accounted for. Samples were obtained from 306 female reindeer that were culled and genotyped at nine microsatellite loci. Reindeer in our study populations are mainly parasitized by the gastrointestinal nematodes Ostertagia gruehneri and Marshallagia marshalli. The infection intensity of each parasite differed between subpopulations, and among host age classes, seasons and years. We found no significant relationships between abomasal worm burdens, or lumen and mucosa larvae, of either O. gruehneri or M. marshalli and individual heterozygosity (or mean d(2)) alone or in interactions with host age, locality, and year. Although we analysed one of the largest data set available to date on gastrointestinal nematodes of a wild ruminant, we used a typical data set of nine genetic neutral markers that may have had low power to detect heterozygosity-fitness correlations. We conclude that the proportion of the variance in parasite resistance explained by individual heterozygosity for neutral genetic markers is low in Svalbard reindeer and in vertebrates in general, and we suggest that the candidate-gene approach might be more fruitful for further research on gene-fitness correlations.     

Functional relationship between sealworm (Pseudoterranova decipiens, Nematoda, Ascaridoidea) burden and host size in Atlantic cod (Gadus morhua).

A model is proposed to describe the accumulation of sealworm parasites (Pseudoterranova decipiens, Nematoda, Ascaridoidae) in Atlantic cod (Gadus morhua). The model predicts the total amount of food eaten by a fish to reach its size. In young fish growth is linear in time and average parasite burdens are predicted to increase with the cube of the average length of the fish divided by its growth rate. An analysis of worm burdens in cod caught by the commercial fishery in the Firth of Clyde (Strathclyde, Scotland) between 1964 and 1970 illustrates how average parasite abundances at age, length, or fixed time of the year can be compared. It is concluded that exposure did not vary significantly over these years. Extensive apparent inter-annual variations in worm burdens of cod newly recruited to the fishery are well explained by differences in the age composition of cod catches.     

Parasite burdens differ between sympatric three-spined stickleback species

The ecological theory of adaptive radiation states that differences in ecological circumstances among local populations are the cause of divergence that leads to speciation. The role of parasites in contributing to divergence has seldom been considered, despite their ubiquity and known selective effects. The potential for parasites to contribute to divergence between closely related taxa was examined by quantifying the variation in parasite burdens between sympatric three-spined stickleback species ( Gasterosteus aculeatus complex) in two lakes in coastal British Columbia, Canada. In doing so the relative importance of geographical differences between lakes and trophic or microhabitat differences between species within lakes were evaluated. The entire metazoan parasite burdens of a total of 255 limnetic and benthic sticklebacks in Paxton and Priest lakes were assayed over five time points between spring and autumn. Despite their sympatric distributions, there were large differences in parasite burdens between benthic and limnetic sticklebacks within lakes and these were consistent across both lakes. In particular, limnetics suffered greater burdens of the parasites Schistocephalus solidus and Diplostomum scudderi and benthics had much higher burdens of parasitic glochidia (mollusc larvae). Parasite burdens also differed quantitatively between lakes, but in general such differences were less pronounced than those between the stickleback species. The documented differences in parasite burdens between stickleback species have potential to contribute to divergent selection on life history, immunological and secondary sexual characters that could contribute to reproductive isolation between the species.     

Parasites as biological tags for Eleginops maclovinus (Teleostei: Eleginopidae) around the Falkland Islands

This is the first study of the parasite fauna of Eleginops maclovinus in the Falkland Islands. It was undertaken to catalogue the parasite fauna of E. maclovinus in order to provide a baseline for future studies and to determine whether parasites might be used as biological tags. Between 21 January and 17 March 2002 samples were taken from three stations, Teal Creek (30 fish), Port Louis (30 fish) and Camilla Creek (10 fish), all in East Falkland, and examined for protozoan and metazoan parasites. Twenty-four parasite taxa were recorded, of which three were possible new species, two new host records and five new geographical records. Because of the small number of fish in the Camilla Creek sample it was excluded from further analyses. E. maclovinus is a protandrous hermaphrodite and all fish greater than 53 cm total length were found to be female, so these too were excluded from further analyses. The parasite data from the remaining fish were analysed by an agglomerative hierarchical cluster analysis using an average linkage and a Jaccard measure of similarity, followed by a linear discriminant function analysis (LDA). Both analyses misclassified only one fish from Port Louis as being from Teal Creek, with the LDA giving an overall correct classification of 97.5% (39/40). The results support mechanical tagging data in suggesting that smaller male E. maclovinus are resident in the creeks in which they are caught, and that at this stage of their lives they tend not to migrate over long distances.     

Tannins and self-medication: Implications for sustainable parasite control in herbivores

Animals adapt to the variability of the external environment and to their changing internal needs not only by generating homeostatic physiological responses, but also by operating in the external environment. In this study, we determined whether sheep with a gastrointestinal parasite infection increased intake of a low-quality food containing a natural antiparasitic agent (tannins) relative to non-parasitized sheep. Four groups of lambs (n = 8 lambs/group) were assigned to a 2 × 2 factorial design with parasitic burden (P = parasites; NP = no parasites) and the offer of a supplement containing tannins (yes, no) as the main factors. Parasitized lambs ate more of the tannin-containing food than non-parasitized lambs for the first 12 days of the study, when parasite burdens were high, but differences became smaller and disappeared toward the end of the study when parasite burdens decreased. This result suggests the lambs detected the presence of internal parasites or associated symptoms and modified their ingestion of an antiparasitic agent as a function of need.     

Studies on the biology of Eubothrium salvelini and E. crassum in resident and migratory Salvelinus alpinus and Salmo trutta and in S. salar in North Norway and the islands of Spitsbergen and Jan Mayen

Samples of Eubothrium salvelini and E. crassum were obtained from resident and migratory Salvelinus alpinus and Salmo trutta and from S. salar at sea from North Norway and the islands of Spitsbergen and Jan Mayen. Scolex dimensions proved an unsuitable character for identifying these two parasite species, and use of alternative characters confirmed that E. salvelini is specific to Salvelinus and E. crassum to Salmo. Distributions of both species are co-extensive with their hosts, but levels of infection in any locality relate to the abundance of zooplankton. E. salvelini exhibits seasonal maturation and incidence cycles in char. It is recognised as being a freshwater parasite, although some individuals can survive the period of marine migration of sea char. Returning migrant char may contain such individuals together with small plerocerciform parasites acquired almost immediately upon their re-entry to freshwater. No evidence for marine infections with E. salvelini was found. The presence of plerocerciform and gravid adult E. crassum in salmon caught at sea confirms the existence of a marine life cycle and a marine race in this species. In salmon moving from one medium to the other the marine and freshwater races replace each other, but in sea trout, which spend shorter periods at sea, complete replacement may not occur and at any one time fish may harbour individuals of both races. Recognition of the existence of two races clarifies much of the confusion surrounding the biology of this species.     

Preliminary study on genetic variability of Dicrocoelium dendriticum determined by random amplified polymorphic DNA

Genetic variability of adult specimens of Dicrocoelium dendriticum has been studied using random amplified polymorphic DNA (RAPD). The worms were collected from the infected livers of different sheep from several localities in León province (NW Spain). DNA fragments were amplified by means of decamer primer oligonucleotides of arbitrary sequence. Some primers produce complex and highly variable patterns of amplified DNA in D. dendriticum. Intra- and inter-population genetic variability of adult parasites were analyzed, scoring polymorphic and monomorphic reproducible bands by means of the Jaccard similarity, and dendrograms showing genetic relationships between individuals were obtained using the FITCH method. Genetic variability seems to be high in this parasite and genetic similarity within a population (worms infecting a single animal) is similar to the average similarity between worms from different sheep. These results suggest that each sheep is infected by numerous genetically different parasites from one or more populations of infected ants.     

Length–weight relationships for two abundant rocky reef fishes from northern Patagonia,Argentina: Sebastes oculatus Valenciennes, 1833 and Pinguipes brasilianus Cuvier, 1829

The Patagonian rockfish Sebastes oculatus and the Brazilian sandperch Pinguipes brasilianus are two of the most abundant, conspicuous reef fishes in the northern Patagonian gulfs of Argentina. This study provides separate length–weight relationships for males, females and pooled individuals of these species for the North Patagonian region, based on samples collected between 2009 and 2014 throughout the year between 42°S and 45°S. No length–weight relationships for P. brasilianus were heretofore available in the literature. Although one relationship was published for S. oculatus from Chilean waters, the limited number of fish and size range did not allow an accurate estimate of the model parameters.