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Britt-Marie B, Sara P, Suzanne F, Frank RF, Anna RM. Temporal and Geographical Variation of Intestinal Ulcers in Grey Seals ( Halichoerus grypus) and Environmental Contaminants in Baltic Biota during Four Decades. Animals (Basel) 2021; 11:ani11102968. [PMID: 34679987 PMCID: PMC8532654 DOI: 10.3390/ani11102968] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/08/2021] [Accepted: 10/12/2021] [Indexed: 01/07/2023] Open
Abstract
Simple Summary In the 1970s it was discovered that seal populations in the Baltic Sea had decreased severely due to hunting and high levels of contaminants. Lesions were found in several organs and many of the females became sterile. Since then, most of the organ lesions have decreased and so have the levels of some pollutants. However, ulcers in the large intestines of the grey seals increased in the early 1980s and decreased after the mid-1990s. The aims of this study were to: (1) describe the ulcers and investigate if there is a trend over time that coincides with concentrations of some pollutants in Baltic biota; (2) evaluate the significance of different sea areas in the Baltic, grade of parasite intensity, as well as the sex and age of the seals. The results show that seals with ulcers had, in general, higher parasite intensity. Ulcers were more common in older seals and in the Bothnian Sea. The time trend of ulcers coincides with the trend of certain contaminant levels (BDE-47, PFOS and cadmium). The high prevalence of intestinal ulcers and the high intensity of acanthocephalan parasites appear to be unique to the Baltic population of grey seals. Abstract The prevalence of intestinal ulcers and parasites was investigated in 2172 grey seals (Halichoerus grypus) collected in the Baltic Sea and 49 grey seals collected outside the Baltic Sea (i.e., the Atlantic). An increase in frequency of ileocaeco-colonic ulcers was observed in the early 1980s, followed by a decrease in the mid-1990s. At the same time, there was an increase followed by a decrease in brominated flame retardants, Perfluorooctanesulfonic acid (PFOS) and cadmium levels in herring (Clupea harengus), the most common prey item in Baltic grey seal diet, as well as in another top predator in the Baltic, the common guillemot (Uria aalge). The frequency of intestinal ulcers was significantly related to the intensity of acanthocephalan parasites, the age of the seal and the region of the Baltic Sea. Perforation of the intestinal wall was the cause of death in 26 of the investigated Baltic grey seals. In contrast, none of the investigated Atlantic grey seals had intestinal ulcers. They showed a thin colonic wall and very few acanthocephalan parasites. The high prevalence of intestinal ulcers and the high parasite intensity appear to be unique to the Baltic population of grey seals.
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Affiliation(s)
- Bäcklin Britt-Marie
- Department of Environmental Research and Monitoring, Swedish Museum of Natural History, P.O. Box 50007, SE 104 05 Stockholm, Sweden; (P.S.); (F.S.); (R.M.A.)
- Correspondence: ; Tel.: +46-851-954-259
| | - Persson Sara
- Department of Environmental Research and Monitoring, Swedish Museum of Natural History, P.O. Box 50007, SE 104 05 Stockholm, Sweden; (P.S.); (F.S.); (R.M.A.)
| | - Faxneld Suzanne
- Department of Environmental Research and Monitoring, Swedish Museum of Natural History, P.O. Box 50007, SE 104 05 Stockholm, Sweden; (P.S.); (F.S.); (R.M.A.)
| | - Rigét F. Frank
- Department of Ecoscience, Danish Centre for Environment and Energy, Arctic Research Centre, Aarhus University, Frederiksborgvej 399, 4000 Roskilde, Denmark;
| | - Roos M. Anna
- Department of Environmental Research and Monitoring, Swedish Museum of Natural History, P.O. Box 50007, SE 104 05 Stockholm, Sweden; (P.S.); (F.S.); (R.M.A.)
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Nyman T, Papadopoulou E, Ylinen E, Wutke S, Michell CT, Sromek L, Sinisalo T, Andrievskaya E, Alexeev V, Kunnasranta M. DNA barcoding reveals different cestode helminth species in northern European marine and freshwater ringed seals. INTERNATIONAL JOURNAL FOR PARASITOLOGY-PARASITES AND WILDLIFE 2021; 15:255-261. [PMID: 34277335 PMCID: PMC8261468 DOI: 10.1016/j.ijppaw.2021.06.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 06/14/2021] [Accepted: 06/21/2021] [Indexed: 02/08/2023]
Abstract
Three subspecies of the ringed seal (Pusa hispida) are found in northeastern Europe: P. h. botnica in the Baltic Sea, P. h saimensis in Lake Saimaa in Finland, and P. h. ladogensis in Lake Ladoga in Russia. We investigated the poorly-known cestode helminth communities of these closely related but ecologically divergent subspecies using COI barcode data. Our results show that, while cestodes from the Baltic Sea represent Schistocephalus solidus, all worms from the two lakes are identified as Ligula intestinalis, a species that has previously not been reported from seals. The observed shift in cestode communities appears to be driven by differential availability of intermediate fish host species in marine vs. freshwater environments. Both observed cestode species normally infect fish-eating birds, so further work is required to elucidate the health and conservation implications of cestode infections in European ringed seals, whether L. intestinalis occurs also in marine ringed seals, and whether the species is able to reproduce in seal hosts. In addition, a deep barcode divergence found within S. solidus suggests the presence of cryptic diversity under this species name. COI barcoding reveals different cestodes in marine and freshwater ringed seals. Ligula intestinalis is reported for the first time from seals. A deep barcode divergence is found within Schistocephalus solidus in the Baltic Sea.
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Affiliation(s)
- Tommi Nyman
- Department of Ecosystems in the Barents Region, Norwegian Institute of Bioeconomy Research, Svanvik, Norway
| | - Elena Papadopoulou
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
| | - Eeva Ylinen
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
| | - Saskia Wutke
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
| | - Craig T Michell
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
| | - Ludmila Sromek
- Department of Marine Ecosystems Functioning, Institute of Oceanography, University of Gdansk, Gdynia, Poland
| | - Tuula Sinisalo
- Department of Biological and Environmental Sciences, University of Jyväskylä, Jyväskylä, Finland
| | | | | | - Mervi Kunnasranta
- Natural Resources Institute Finland, Joensuu, Finland.,Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
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Leidenberger S, Boström S, Wayland MT. Host records and geographical distribution of Corynosoma magdaleni, C. semerme and C. strumosum (Acanthocephala: Polymorphidae). Biodivers Data J 2020; 8:e50500. [PMID: 32308529 PMCID: PMC7154045 DOI: 10.3897/bdj.8.e50500] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 03/30/2020] [Indexed: 12/02/2022] Open
Abstract
A literature survey was conducted to investigate the host and geographical distribution patterns of three Corynosoma species (Acanthocephala: Polymorphidae), viz. C.magdaleni, C.semerme and C.strumosum. All three species appear to be restricted to the Northern Hemisphere. Occurrence records of C.magdaleni are limited to the Northern Atlantic coasts, while C.semerme has a circumpolar distribution. The geographical range of Corynosomastrumosum encompasses the distributions of the other two species, but also extends into warmer southern regions. Some Corynosoma populations are living with their definitive hosts in very isolated locations, such as in the brackish Baltic Sea or different freshwater lakes (e.g. Lake Saimaa). All three species have a heteroxenous life cycle, comprising a peracaridan intermediate host, a fish paratenic host and a mammalian definitive host. Occasionally, an acanthocephalan may enter an accidental host, from which it is unable to complete its life cycle. The host records reported here are categorised by type, i.e. intermediate, paratenic, definitive or accidental. While most of the definitive hosts are shared amongst the three Corynosoma species, C.strumosum showed the broadest range of paratenic hosts, which reflects its more extensive geographical distribution. One aim of this study and extensive literature summary is to guide future sampling efforts and therewith contribute to throw more light on the on-going species and morphotype discussion for this interesting parasite species.
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Affiliation(s)
- Sonja Leidenberger
- School of Bioscience, Department of Biology and Bioinformatics, University of Skövde, Skövde, Sweden School of Bioscience, Department of Biology and Bioinformatics, University of Skövde Skövde Sweden
| | - Sven Boström
- Swedish Museum of Natural History, Department of Zoology, Stockholm, Sweden Swedish Museum of Natural History, Department of Zoology Stockholm Sweden
| | - Matthew Thomas Wayland
- University of Cambridge, Cambridge, United Kingdom University of Cambridge Cambridge United Kingdom
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Scholz T, Kuchta R, Brabec J. Broad tapeworms (Diphyllobothriidae), parasites of wildlife and humans: Recent progress and future challenges. Int J Parasitol Parasites Wildl 2019; 9:359-369. [PMID: 31341771 PMCID: PMC6630034 DOI: 10.1016/j.ijppaw.2019.02.001] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 01/31/2019] [Accepted: 02/01/2019] [Indexed: 02/08/2023]
Abstract
Tapeworms of the family Diphyllobothriidae, commonly known as broad tapeworms, are predominantly large-bodied parasites of wildlife capable of infecting humans as their natural or accidental host. Diphyllobothriosis caused by adults of the genera Dibothriocephalus, Adenocephalus and Diphyllobothrium is usually not a life-threatening disease. Sparganosis, in contrast, is caused by larvae (plerocercoids) of species of Spirometra and can have serious health consequences, exceptionally leading to host's death in the case of generalised sparganosis caused by 'Sparganum proliferum'. While most of the definitive wildlife hosts of broad tapeworms are recruited from marine and terrestrial mammal taxa (mainly carnivores and cetaceans), only a few diphyllobothriideans mature in fish-eating birds. In this review, we provide an overview the recent progress in our understanding of the diversity, phylogenetic relationships and distribution of broad tapeworms achieved over the last decade and outline the prospects of future research. The multigene family-wide phylogeny of the order published in 2017 allowed to propose an updated classification of the group, including new generic assignment of the most important causative agents of human diphyllobothriosis, i.e., Dibothriocephalus latus and D. nihonkaiensis. Genomic data of selected representatives have also begun to accumulate, promising future developments in understanding the biology of this particular group of parasites. The list of nominal species of taxonomically most complicated genus Spirometra as well as host-parasite list of 37 species of broad tapeworms parasitising marine mammals (pinnipeds and cetaceans) are also provided.
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Affiliation(s)
- Tomáš Scholz
- Institute of Parasitology, Biology Centre of the Czech Academy of Sciences, Branišovská 31, 370 05, České Budějovice, Czech Republic
| | - Roman Kuchta
- Institute of Parasitology, Biology Centre of the Czech Academy of Sciences, Branišovská 31, 370 05, České Budějovice, Czech Republic
| | - Jan Brabec
- Institute of Parasitology, Biology Centre of the Czech Academy of Sciences, Branišovská 31, 370 05, České Budějovice, Czech Republic
- Natural History Museum of Geneva, PO Box 6434, CH-1211, Geneva 6, Switzerland
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Aznar FJ, Hernández-Orts JS, Raga JA. Morphology, performance and attachment function in Corynosoma spp. (Acanthocephala). Parasit Vectors 2018; 11:633. [PMID: 30545426 PMCID: PMC6293589 DOI: 10.1186/s13071-018-3165-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 10/22/2018] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Functional inference on the attachment of acanthocephalans has generally been drawn directly from morphology. However, performance of structures is often non-intuitive and context-dependent, thus performance analysis should be included whenever possible to improve functional interpretation. In acanthocephalans, performance analysis of attachment is available only for Acanthocephalus ranae, a species that solely relies on the proboscis to attach. Here we compare body morphology and muscle arrangement in 13 species of Corynosoma, which use their spiny body as a fundamental holdfast. A basic performance analysis using live cystacanths of two representative species is also provided. METHODS Adults of 13 Corynosoma spp. were obtained from 11 marine mammal species. Specimens were cut and carefully cleaned to examine muscle arrangement through light and scanning electron microscopy. Live cystacanths of C. australe and C. cetaceum were selected for performance analysis. Video records of evagination-invagination cycles of the proboscis were obtained and analysed with a video editor. RESULTS The basic arrangement of proboscis retractors, trunk circular and longitudinal muscles, neck retractors and receptacle retractors, was conserved in all Corynosoma species. Interspecific variability was found in the relative development of disk muscles: minimum in C. enhydri, maximum in C. cetaceum; the distal insertion of the ventral neck retractor: ventro-lateral in C. cetaceum, C. hamannni and C. pseudohamanni and ventral in the other species; and the distal insertion of the receptacle retractors: more proximal in species with a longer hindtrunk. Performance analysis indicated striking similarities to that described for A. ranae except that (i) the foretrunk bends ventrally during the evagination-invagination cycles of the proboscis; (ii) disk muscles can flatten the tip of the foretrunk regardless of these cycles; and (iii) the receptacle bends ventrally and is driven to the hindtrunk by coordinated action of receptacle retractors. CONCLUSIONS Species of Corynosoma are able to use up to six holfast mechanisms. Attachment relies on a similar performance to that described for A. ranae. However, structural ventral bending of an inflated, spiny foretrunk, with a parallel re-arrangement of foretrunk muscles, have generated unexpected novel functions that make attachment extremely effective in species of Corynosoma. Interspecific variability in trunk shape and muscle arrangement grossly correlates with the rheological conditions each species experiences in their microhabitats within the gut of marine mammals.
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Affiliation(s)
- Francisco Javier Aznar
- Instituto Cavanilles de Biodiversidad y Biología Evolutiva, Parque Científico, Universidad de Valencia, Catedrático José Beltrán 2, 46980, Paterna, Valencia, España.
| | - Jesús Servando Hernández-Orts
- Centro de Investigación Aplicada y Transferencia Tecnológica en Recursos Marinos Almirante Storni (CIMAS - CCT CONICET - CENPAT), Güemes 1030, 8520, San Antonio Oeste, Río Negro, Argentina
| | - Juan Antonio Raga
- Instituto Cavanilles de Biodiversidad y Biología Evolutiva, Parque Científico, Universidad de Valencia, Catedrático José Beltrán 2, 46980, Paterna, Valencia, España
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Haukisalmi V. Checklist of tapeworms (Platyhelminthes, Cestoda) of vertebrates in Finland. Zookeys 2015:1-61. [PMID: 26668540 PMCID: PMC4669923 DOI: 10.3897/zookeys.533.6538] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Accepted: 10/09/2015] [Indexed: 12/04/2022] Open
Abstract
A checklist of tapeworms (Cestoda) of vertebrates (fishes, birds and mammals) in Finland is presented, based on published observations, specimens deposited in the collections of the Finnish Museum of Natural History (Helsinki) and the Zoological Museum of the University of Turku, and additional specimens identified by the present author. The checklist includes 170 tapeworm species from 151 host species, comprising 447 parasite species/host species combinations. Thirty of the tapeworm species and 96 of the parasite/host species combinations have not been previously reported from Finland. The total number of tapeworm species in Finland (170 spp.) is significantly lower than the corresponding figure for the Iberian Peninsula (257 spp.), Slovakia (225 spp.) and Poland (279 spp.). The difference between Finland and the other three regions is particularly pronounced for anseriform, podicipediform, charadriiform and passeriform birds, reflecting inadequate and/or biased sampling of these birds in Finland. It is predicted that there are actually ca. 270 species of tapeworms in Finland, assuming that true number of bird tapeworms in Finland corresponds to that in other European countries with more comprehensive knowledge of the local tapeworm fauna. The other main pattern emerging from the present data is the seemingly unexplained absence in (northern) Fennoscandia of several mammalian tapeworms that otherwise have extensive distributions in the Holarctic region or in Eurasia, including the northern regions. Previously unknown type specimens, that is, the holotype of Bothrimonusnylandicus Schneider, 1902 (a junior synonym of Diplocotyleolrikii Krabbe, 1874) (MZH 127096) and the syntypes of Caryophyllaeidesfennica (Schneider, 1902) (MZH 127097) were located in the collections of the Finnish Museum of Natural History.
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Affiliation(s)
- Voitto Haukisalmi
- Finnish Museum of Natural History Luomus, P. O. Box 17, P. Rautatiekatu 13, 00014 University of Helsinki, Finland
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Hookworms (Uncinaria lucasi) and acanthocephalans (Corynosoma spp. and Bolbosoma spp.) found in dead northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska in 2007. Parasitol Res 2008; 103:1025-9. [PMID: 18587686 DOI: 10.1007/s00436-008-1087-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2008] [Accepted: 06/08/2008] [Indexed: 10/21/2022]
Abstract
Intestines of dead northern fur seals (Callorhinus ursinus) on St. Paul Island (SPI), Alaska were inspected for specific internal parasites (hookworms and acanthocephalans) in July and August, 2007. Pups (n=64) were examined for adult hookworms (Uncinaria lucasi) and four (6.25%) were infected. The number of specimens per infected pup was 1, 2, 2, or 408. Low prevalence was similar to that determined in the last investigation (2001) in dead fur seal pups on SPI by two of the present authors (Lyons and Spraker). Subadult males (SAMS-3-4 years old, n=115) were examined for acanthocephalans and 25 (21.7.0%) were infected. Adult Corynosoma (C. obtuscens, C. strumosum, and C. validum) (n=56) and immature Bolbosoma spp. (n=4) were found. Apparently, this is a new host record for C. obtuscens and C. validum. Notes were made on finding tapeworms. in 114 of the 115 SAMs. Examination of some specimens revealed scolices characteristic of Diphyllobothrium spp.
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Sinisalo T, Valtonen ET, Helle E, Jones RI. Combining stable isotope and intestinal parasite information to evaluate dietary differences between individual ringed seals (Phoca hispida botnica). CAN J ZOOL 2006. [DOI: 10.1139/z06-067] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The diet and foraging behaviour of nine individual Baltic ringed seals ( Phoca hispida botnica Gmelin, 1785) in the Bothnian Bay were studied by combining results from stable isotope analyses (δ13C and δ15N) with data on intestinal parasites whose occurrence varied among the fish hosts. The patterns of infection with three acanthocephalan parasites, Corynosoma semerme (Forssell, 1904), Corynosoma magdaleni Montreuil, 1958, and Corynosoma strumosum (Rudolphi, 1802), and with a cestode larva, Schistocephalus solidus (Müller, 1776), were examined. The ringed seals become infected with these intestinal parasites by feeding on the fish hosts and hence have different parasite species and different parasite burdens according to their dietary history. δ13C and δ15N values were determined from diaphragm muscle of the seals and from tissues of potential prey items. A dual isotope plot of δ13C and δ15N values for individual seals and mean values for key potential prey species, together with the parasitological data from the seals, allowed inferences to be drawn about the feeding of individual seals. It appeared that two seals foraged particularly on fourhorn sculpin ( Myoxocephalus quadricornis (L., 1758)) and one seal consumed a high proportion of the isopod Saduria entomon (L., 1758). Three seals apparently preferred coastal benthic prey in their diets, while two other seals fed more on pelagic herring ( Clupea harengus membras L., 1761). One older female seal evidently also fed on salmon ( Salmo salar L., 1758).
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Affiliation(s)
- Tuula Sinisalo
- Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FIN-40014 University of Jyväskylä, Finland
- Finnish Game and Fisheries Research Institute, P.O. Box 2, FIN-00791 Helsinki, Finland
| | - E. Tellervo Valtonen
- Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FIN-40014 University of Jyväskylä, Finland
- Finnish Game and Fisheries Research Institute, P.O. Box 2, FIN-00791 Helsinki, Finland
| | - Eero Helle
- Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FIN-40014 University of Jyväskylä, Finland
- Finnish Game and Fisheries Research Institute, P.O. Box 2, FIN-00791 Helsinki, Finland
| | - Roger I. Jones
- Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FIN-40014 University of Jyväskylä, Finland
- Finnish Game and Fisheries Research Institute, P.O. Box 2, FIN-00791 Helsinki, Finland
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Valtonen ET, Helle E, Poulin R. Stability ofCorynosomapopulations with fluctuating population densities of the seal definitive host. Parasitology 2004; 129:635-42. [PMID: 15552408 DOI: 10.1017/s0031182004005839] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In theory there should be a strong coupling between host and parasite population sizes. Here, we investigated population size and structure in 3 species of acanthocephalans,Corynosoma semerme,C. strumosumandC. magdaleni, in ringed seals (Phoca hispida) from the Bothnian Bay over a period of more than 20 years. During this period, seal numbers first decreased markedly and then increased steadily; at the same time, a paratenic fish host particularly important forC. strumosumhas gradually disappeared from the bay due to decreasing salinity. We found no evidence that the mean abundance of any of the 3 acanthocephalan species changed significantly over time, nor was there any relationship between parasite abundance at any point in time and seal numbers in the corresponding year. Based on the proportion of sexually mature female worms per infrapopulation, and on relationships between the sex ratio of worms and infrapopulation size, bothC. magdaleniandC. semermeappear to be doing well, independently of the population size of their seal definitive hosts. In contrast, perhaps because of the loss of its main paratenic host,C. strumosumappears more at risk in the Bothnian Bay. Our results show that in complex natural systems, there are not necessarily simple, direct links between definitive host population size or density, and parasite population dynamics.
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Affiliation(s)
- E T Valtonen
- Department of Biological and Environmental Science, University of Jyväskylä, FIN-40014 University of Jyväskylä, Finland.
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Aznar FJ, Cappozzo HL, Taddeo D, Montero FE, Raga JA. Recruitment, population structure, and habitat selection of Corynosoma australe (Acanthocephala) in South American fur seals, Arctocephalus australis, from Uruguay. CAN J ZOOL 2004. [DOI: 10.1139/z04-044] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We analysed recruitment, population structure, and intestinal distribution of Corynosoma australe Johnston, 1937 in 27 South American fur seals, Arctocephalus australis (Zimmerman, 1783), collected in two Uruguayan localities during 1990 and 1991. Only heavy infections of C. australe were found in all intestines. High transmission rates might result from the massive concentration of fur seals in the study area and the ecological ubiquity of C. australe. Intestinal length (IL) accounted, through a cubic relationship, for most of the variation (74%) in parasite intensity. IL3 also predicted the percentage of juvenile females among hosts (an indicator of recruitment rate) better than intensity or host body size. Intestinal size might be a suitable surrogate of host metabolic rate, the potential factor influencing intensity. The percentages of females and gravid females significantly increased along the intestine, and the distribution of juvenile females, gravid females, and males significantly covaried after controlling for intensity effects. These patterns suggest that worms migrate towards the lower jejunum and ileum while they mature, copulate, and reproduce. Males and gravid females shifted their distribution anteriad, and gravid females expanded their distribution, with intensity. These patterns might result from recruitment dynamics, intraspecific competition, or both. We do not know why males, gravid females, and juvenile females respond differently to these factors.
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