Freshwater ecosystems in Lithuania are threatened by the introduction of invasive fish species including Neogobius fluviatilis, N. melanostomus, Perccottus glenii, and Pseudorasbora parva. Data on helminth parasites of these fishes have not been comprehensively studied, with only two reports on parasites of N. melanostomus from the Curonian Lagoon and Baltic Sea, Lithuania. We examined 278 fish individuals representing 4 invasive species from 13 waterbodies. Using morphological and molecular analyses, we identified 29 helminth taxa representing 15 digenean trematodes, 6 nematodes, 4 cestodes, 2 acanthocephalans, and 2 monogeneans. With 18 species, N. fluviatilis had the highest helminth diversity, followed by N. melanostomus (11 species) and Ps. parva (8 species). Perccottus glenii was found to be free from helminth infection. The availability of historical information on the native fish parasites in Lithuania allowed us to conclude that out of the 29 recorded species, invasive fish serve as hosts for 22 local fish helminth species, while 7 helminth species have been reported exclusively in invasive fish. Based on newly obtained and previously published data, a total of 34 helminth species parasitise invasive fish in Lithuania, of which 30 use these fish as intermediate or paratenic hosts.

• Klíčová slova
• Baltic freshwater ecosystems, Neogobius spp., Perccottus glenii, Pseudorasbora parva, aquatic invasion, morphological and molecular identification,
• Publikační typ
• časopisecké články MeSH

Strigea falconis is a common parasite of birds of prey and owls widely distributed in the Holarctic. We aimed to characterise S. falconis from Iceland via integrative taxonomic approach and to contribute to the understanding of its circulation in the Holarctic. We recovered adult S. falconis from two gyrfalcons (Falco rusticolus) collected in 2011 and 2012 in Iceland (Reykjanes Peninsula, Westfjords) and characterised them by morphological and molecular genetic (D2 of rDNA, cox1, ND1 of the mDNA) methods. We provide the first species record of S. falconis in Iceland which to the best of our knowledge is its northernmost distributional range. The presence of S. falconis in Iceland is surprising, as there are no suitable intermediate hosts allowing completion of its life cycle. Gyrfalcons are fully sedentary in Iceland; thus, the only plausible explanation is that they acquired their infection by preying upon migratory birds arriving from Europe. Our data indicate that the most likely candidates are Anseriformes and Charadriiformes. Also, we corroborate the wide geographical distribution of S. falconis, as we found a high degree of similarity between our haplotypes and sequences of mesocercariae from frogs in France and of a metacercaria from Turdus naumanni in Japan, and adults from Buteo buteo and Circus aeruginosus from the Czech Republic. The case of Strigea falconis shows the advantages of a complex life cycle and also depicts its pitfalls when a parasite is introduced to a new area with no suitable intermediate hosts. In Iceland, gyrfalcons are apparently dead-end hosts for S. falconis.

• Klíčová slova
• Digenea, Gyrfalcon, Life cycle, Nuclear and mitochondrial DNA, Raptors, Trematoda,
• MeSH
• Falconiformes * MeSH
• stadia vývoje MeSH
• Trematoda * genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• Evropa MeSH
• Island epidemiologie   MeSH

We compared three sets of highly resolved food webs with and without parasites for a subarctic lake system corresponding to its pelagic and benthic compartments and the whole-lake food web. Key topological food-web metrics were calculated for each set of compartments to explore the role parasites play in food-web topology in these highly contrasting webs. After controlling for effects from differences in web size, we observed similar responses to the addition of parasites in both the pelagic and benthic compartments demonstrated by increases in trophic levels, linkage density, connectance, generality, and vulnerability despite the contrasting composition of free-living and parasitic species between the two compartments. Similar effects on food-web topology can be expected with the inclusion of parasites, regardless of the physical characteristics and taxonomic community compositions of contrasting environments. Additionally, similar increases in key topological metrics were found in the whole-lake food web that combines the pelagic and benthic webs, effects that are comparable to parasite food-web analyses from other systems. These changes in topological metrics are a result of the unique properties of parasites as infectious agents and the links they participate in. Trematodes were key contributors to these results, as these parasites have distinct characteristics in aquatic systems that introduce new link types and increase the food web's generality and vulnerability disproportionate to other parasites. Our analysis highlights the importance of incorporating parasites, especially trophically transmitted parasites, into food webs as they significantly alter key topological metrics and are thus essential for understanding an ecosystem's structure and functioning.

• Klíčová slova
• Connectance, Food webs, Parasite ecology, Trematoda, Trophic transmission,
• MeSH
• ekosystém * MeSH
• jezera MeSH
• paraziti * MeSH
• potraviny MeSH
• potravní řetězec MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

Cercariae, the free-living larval stages of trematodes, have adopted an amazing variety of transmission strategies. One of them is prey-mimetism, i.e. cercariae mimicking prey to attract motile hosts to be eaten. In a period between 2002 and 2019, we examined small planorbid snails, Bathyomphalus contortus, Gyraulus parvus and Planorbis planorbis from lakes in Finland and Iceland and from the Curonian Lagoon in Lithuania. Cercariae with conspicuously enlarged tails and unusual swimming behaviour, likely mimicking invertebrate prey, were detected and studied by the use of morphological and molecular (cox1, ITS1-5.8S-ITS2 and 28S rDNA) methods. Cercariae of two species belonging to the genus Apatemon (Strigeidae) were recognised. We consider Apatemon sp. 5 ex P. planorbis from the Curonian Lagoon identical to Cercaria globocaudata U. Szidat, 1940. Cercariae ex G. parvus from Iceland and ex B. contortus from Finland were conspecific, and we named them Apatemon sp. 6; these cercariae could not be associated with any known species. For the first time, we verified that cercariae of the Bulbocauda group belong to the genus Apatemon. We provide a mini-review on records of furcocercariae of the family Strigeidae with enlarged tails reported in freshwaters of the northern hemisphere and reveal that it is not only Apatemon but also Australapatemon and most likely Strigea which belong to the Bulbocauda group, rendering it a purely ecological assemblage. Understanding which invertebrate swimming behaviour these cercariae are mimicking will enhance our knowledge of the processes behind trematode transmission and will help to assess evolutionary pathways of host-finding strategies in trematodes.

• Klíčová slova
• Behaviour, Digenea, Europe, Freshwater, Nuclear and mitochondrial DNA, Trematoda,
• MeSH
• cerkárie genetika   MeSH
• hlemýždi MeSH
• jezera MeSH
• Trematoda * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

The emergence of cercariae from infected mollusks is considered one of the most important adaptive strategies for maintaining the trematode life cycle. Short transmission opportunities of cercariae are often compensated by periodic daily rhythms in the cercarial release. However, there are virtually no data on the cercarial emergence of bird schistosomes from freshwater ecosystems in northern latitudes. We investigated the daily cercarial emergence rhythms of the bird schistosome Trichobilharzia sp. "peregra" from the snail host Radix balthica in a subarctic lake under both natural and laboratory seasonal conditions. We demonstrated a circadian rhythm with the highest emergence during the morning hours, being seasonally independent of the photo- and thermo-period regimes of subarctic summer and autumn, as well as relatively high production of cercariae at low temperatures typical of northern environments. These patterns were consistent under both field and laboratory conditions. While light intensity triggered and prolonged cercarial emergence, the temperature had little effect on cercarial rhythms but regulated seasonal output rates. This suggests an adaptive strategy of bird schistosomes to compensate for the narrow transmission window. Our results fill a gap in our knowledge of the transmission dynamics and success of bird schistosomes under high latitude conditions that may serve as a basis for elucidating future potential risks and implementing control measures related to the spread of cercarial dermatitis due to global warming.

• Klíčová slova
• Trichobilharzia, bird schistosome, cercariae, emergence, light, temperature, trematodes,
• Publikační typ
• časopisecké články MeSH

Cercarial activity and survival are crucial traits for the transmission of trematodes. Temperature is particularly important, as faster depletion of limited cercarial energy reserves occurs at high temperatures. Seasonal climate conditions in high latitude regions may be challenging to complete trematode life cycle during the 6-month ice-free period, but temperature effects on the activity and survival of freshwater cercariae have not been previously identified. After experimentally simulating natural subarctic conditions during warmer and colder months (13 and 6°C), a statistical approach identifying changes in the tendency of cercarial activity loss and mortality data was used to detect differences in three trematode genera, represented by four taxa (Diplostomum spp., Apatemon spp., small- and large-sized Plagiorchis spp.). A strong temperature-dependent response was identified in both activity loss and mortality in all taxa, with Diplostomum spp. cercariae showing the most gradual changes compared to other taxa. Furthermore, whilst activity loss and mortality dynamics could not be divided into ‘fish- vs invertebrate-infecting cercariae’ groups, the detected taxa-specific responses in relation to life-history traits indicate the swimming behaviour of cercariae and energy allocation among larvae individuals as the main drivers. Cercariae exploit the short transmission window that allows a stable continuance of trematodes’ life cycles in high-latitude freshwater ecosystems.

• Klíčová slova
• High latitude regions, larval stages, life cycle, parasite, transmission strategies,
• MeSH
• cerkárie fyziologie   MeSH
• ekosystém * MeSH
• sladká voda MeSH
• teplota MeSH
• Trematoda * fyziologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Phenotypic polymorphism is a commonly observed phenomenon in nature, but extremely rare in free-living stages of parasites. We describe a unique case of somatic polymorphism in conspecific cercariae of the bird schistosome Trichobilharzia sp. "peregra", in which two morphs, conspicuously different in their size, were released from a single Radix balthica snail. A detailed morphometric analysis that included multiple morphological parameters taken from 105 live and formalin-fixed cercariae isolated from several naturally infected snails provided reliable evidence for a division of all cercariae into two size groups that contained either large or small individuals. Large morph (total body length of 1368 and 1339 μm for live and formalin-fixed samples, respectively) differed significantly nearly in all morphological characteristics compared to small cercariae (total body length of 976 and 898 μm for live and formalin samples, respectively), regardless of the fixation method. Furthermore, we observed that small individuals represent the normal/commonly occurring phenotype in snail populations. The probable causes and consequences of generating an alternative, much larger phenotype in the parasite infrapopulation are discussed in the context of transmission ecology as possible benefits and disadvantages facilitating or preventing the successful completion of the life cycle.

• Klíčová slova
• Trichobilharzia, bird schistosome, cercariae, phenotype, polymorphism, trematodes,
• Publikační typ
• časopisecké články MeSH

The biodiversity of freshwater ecosystems globally still leaves much to be discovered, not least in the trematode parasite fauna they support. Echinostome trematode parasites have complex, multiple-host life-cycles, often involving migratory bird definitive hosts, thus leading to widespread distributions. Here, we examined the echinostome diversity in freshwater ecosystems at high latitude locations in Iceland, Finland, Ireland and Alaska (USA). We report 14 echinostome species identified morphologically and molecularly from analyses of nad1 and 28S rDNA sequence data. We found echinostomes parasitising snails of 11 species from the families Lymnaeidae, Planorbidae, Physidae and Valvatidae. The number of echinostome species in different hosts did not vary greatly and ranged from one to three species. Of these 14 trematode species, we discovered four species (Echinoparyphium sp. 1, Echinoparyphium sp. 2, Neopetasiger sp. 5, and Echinostomatidae gen. sp.) as novel in Europe; we provide descriptions for the newly recorded species and those not previously associated with DNA sequences. Two species from Iceland (Neopetasiger islandicus and Echinoparyphium sp. 2) were recorded in both Iceland and North America. All species found in Ireland are new records for this country. Via an integrative taxonomic approach taken, both morphological and molecular data are provided for comparison with future studies to elucidate many of the unknown parasite life cycles and transmission routes. Our reports of species distributions spanning Europe and North America highlight the need for parasite biodiversity assessments across large geographical areas.

TITLE: Diversité des Échinostomes (Digenea, Echinostomatidae) chez leurs hôtes mollusques aux latitudes élevées. ABSTRACT: La biodiversité des écosystèmes d’eau douce à l’échelle mondiale laisse encore beaucoup à découvrir, notamment dans la faune parasitaire des trématodes qu’ils abritent. Les parasites trématodes Échinostomes ont des cycles de vie complexes à hôtes multiples impliquant souvent des oiseaux migrateurs comme hôtes définitifs, conduisant ainsi à des distributions étendues. Ici, nous avons examiné la diversité des échinostomes dans les écosystèmes d’eau douce à des latitudes élevées en Islande, Finlande, Irlande et en Alaska (États-Unis). Nous rapportons de séquences de nad1 et d’ADNr 28S morphologiquement et moléculairement à partir d’analyses de données de séquence d’ADNr nad1 et 28S. Nous avons trouvé des échinostomes parasitant les mollusques de 11 espèces des familles Lymnaeidae, Planorbidae, Physidae et Valvatidae. Le nombre d’espèces d’échinostomes dans différents hôtes ne variait pas beaucoup et allait d’une à trois espèces. Sur ces 14 espèces de trématodes, nous avons découvert quatre espèces (Echinoparyphium sp. 1, Echinoparyphium sp. 2, Neopetasiger sp. 5, Echinostomatidae gen. sp.) comme nouvelles pour l’Europe; nous fournissons des descriptions pour les espèces nouvellement signalées et celles qui n’étaient pas précédemment associées à des séquences d’ADN. Deux espèces d’Islande (Neopetasiger islandicus et Echinoparyphium sp. 2) ont été signalées en Islande et en Amérique du Nord. Toutes les espèces trouvées en Irlande sont de nouveaux signalements pour ce pays. Grâce à une approche taxonomique intégrative, des données morphologiques et moléculaires sont fournies à des fins de comparaison avec des études futures afin d’élucider les nombreux cycles de vie et voies de transmission des parasites, qui sont inconnus. Nos données sur la répartition des espèces en Europe et en Amérique du Nord soulignent la nécessité d’évaluer la biodiversité des parasites dans de vastes zones géographiques.

• Klíčová slova
• Europe, Mitochondrial and nuclear DNA, Mollusca, Morphology, North America, Trematoda,
• MeSH
• Echinostomatidae * genetika   MeSH
• ekosystém MeSH
• hlemýždi MeSH
• lidé MeSH
• Trematoda * MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• Evropa MeSH
• Severní Amerika MeSH

Direct consumption on free-living cercariae stages of trematodes by non-host organisms interferes with trematode transmission and leads to reduced infections in the next suitable hosts. Consumer functional responses provide a useful tool to examine relationships between consumption rates and ecologically relevant prey densities, whilst also accounting for abiotic factors that likely influence consumption rates. We investigated how temperature influences the consumer functional response of the amphipod Gammarus lacustris towards the cercariae of three freshwater trematodes (Diplostomum, Apatemon and Trichobilharzia). Amphipods displayed different functional responses towards the parasites, with Type II responses for Diplostomum and Type I responses for Apatemon prey. Temperature did not alter the consumption rate of the amphipod predator. Trichobilharzia was likely consumed at similar proportions as Diplostomum; however, this could not be fully evaluated due to low replication. Whilst Type II responses of invertebrate predators are common to various invertebrate prey types, this is the first time a non-filter feeding predator has been shown to exhibit Type I response towards cercarial prey. The prey-specific consumption patterns of amphipods were related to cercarial distribution in the water column rather than to the size of cercariae or temperature influence. The substantial energy flow into food webs by non-host consumer organisms highlights the importance of understanding the mechanisms that modulate functional responses and direct predation in the context of parasitic organisms.

• Klíčová slova
• Cercariae, Gammarus lacustris, Predator-prey, Transmission interference,
• MeSH
• Amphipoda fyziologie   MeSH
• cerkárie klasifikace   růst a vývoj   fyziologie   MeSH
• druhová specificita MeSH
• infekce červy třídy Trematoda parazitologie   přenos   MeSH
• potravní řetězec MeSH
• predátorské chování klasifikace   fyziologie   MeSH
• teplota MeSH
• Trematoda klasifikace   růst a vývoj   fyziologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

Amphipods are often key species in aquatic food webs due to their functional roles in the ecosystem and as intermediate hosts for trophically transmitted parasites. Amphipods can also host many parasite species, yet few studies address the entire parasite community of a gammarid population, precluding a more dynamic understanding of the food web. We set out to identify and quantify the parasite community of Gammarus lacustris to understand the contributions of the amphipod and its parasites to the Takvatn food web. We identified seven parasite taxa: a direct life cycle gregarine, Rotundula sp., and larval stages of two digenean trematode genera, two cestodes, one nematode, and one acanthocephalan. The larval parasites use either birds or fishes as final hosts. Bird parasites predominated, with trematode Plagiorchis sp. having the highest prevalence (69%) and mean abundance (2.7). Fish parasites were also common, including trematodes Crepidostomum spp., nematode Cystidicola farionis, and cestode Cyathocephalus truncatus (prevalences 13, 6, and 3%, respectively). Five parasites depend entirely on G. lacustris to complete their life cycle. At least 11.4% of the overall parasite diversity in the lake was dependent on G. lacustris, and 16% of the helminth diversity required or used the amphipod in their life cycles. These dependencies reveal that in addition to being a key prey item in subarctic lakes, G. lacustris is also an important host for maintaining parasite diversity in such ecosystems.

• Klíčová slova
• Amphipod, Cestoda, Trematoda, food web, trophically transmitted parasites,
• Publikační typ
• časopisecké články MeSH