Ecological and faunistic analyses of the trematodes of the Little Grebe ( Tachybaptus ruficollis (Pallas

The research was conducted from 1998 to 2019 at the nine water bodies of Azerbaijan. During the study, 94 individuals of the Little Grebes ( Tachybaptus ruficollis (Pallas, 1764)) were examined by the method of complete helminthological dissection. As a result, 12 trematode species belonging to one order, seven families, and eight genera were found: Patagifer bilobus, Petasiger megacantha, P. skrjabini, Echinochasmus coaxatus, E. dietzevi, E. mordax, Mesorchis pseudoechinatus, Cryptocotyle concavum, Metorchis intermedius, Eucotyle cohni, Strigea falconis, Hysteromorpha triloba. Of these, three species ( Petasiger megacantha, Echinochasmus coaxatus and E. dietzevi ) are specific grebe parasites, while the others infect various waterfowl. Except for Strigea falconis , whose cercariae penetrate actively into the bird’s body and transform into metacercarie, all the trematode found are ingested by the birds and mature in their intestine. The grebe, as a fish - eating bird, is infected with six trematode species ( Patagifer bilobus, Petasiger megacantha, Mesorchis pseudoechinatus, Cryptocotyle concavum, Metorchis intermedius, Hysteromorpha triloba ) that parasite in fish at the stage of metacercaria. Other species use aquatic invertebrates as second intermediate hosts. We established that species diversity of the grebe trematodes depended on the reservoir size and the richness of its hydrofauna, increasing with the increase of both factors. The differences between the faunas of grebe trematodes in various water bodies depended on the distance between them and the similarity of their living conditions. S even grebe trematode species ( Petasiger megacantha, P. skrjabini, Echinochasmus coaxatus, E. dietzevi, Cryptocotyle concavum, Metorchis intermedius, Eucotyle cohni ) belong to the northern group of helminthes, while the five species ( Patagifer bilobus, Echinochasmus mordax, Mesorchis pseudoechinatus, Strigea falconis, Hysteromorpha triloba ) are ubiquitous. S outhern trematode species were absent from the examined birds. Presumably, this can be explained by the dominance of grebes from northern populations wintering on the water bodies of Azerbaijan.


Introduction
The Little Grebe (Tachybaptus ruficollis (Pallas, 1764)) is a widespread bird in the internal water bodies of Azerbaijan.It lives on the freshwater bodies and on the coast of the Caspian Sea.Most individuals are migratory; only an insignificant part of the birds spend winter in this region.The grebe feeds on little fish, amphibians, crustaceans, shell-fish and water plants.The helminth fauna of the little grebe in Azerbaijan was studied by S.M. Vaidova (1978), who recorded 11 trematode species throughout the country.Although the study of bird parasites, including grebe trematodes, has theoretical and practical importance, not a single work has been published since that time.

Material and method
The material was collected from 1998 to 2019 at nine water research stations in various regions of Azerbaijan: the Devechi Firth, the Small Gizilagach Bay, the coast of the Absheron Peninsula of the Caspian Sea, the Middle Kura River, the Lower Kura River, the Kura delta, the Mingechevir Reservoir, the Varvara Reservoir, and the Lower Araz River (Fig. 1).The birds and their helminth were studied all year round, but most observations were made in April-June and September-November.As a result, 97 specimens of the little grebe were examined by complete helminthological dissection (the method is described in Dubinina, 1971;Pronina, Pronin, 2007;Musselius et al., 2008;Dorovskikh, Stepanov, 2009).Only adult birds were subjected to autopsies; shooting of birds with scientific purposes was carried out with the permission of the Ministry of Ecology and Natural Resources of the Republic of Azerbaijan.The birds were used in a complex study by ornithologists and parasitologists.Some specimens were obtained from amateur hunters; birds that died from natural causes were also studied.In most cases, the birds were dissected on the spot; some individuals were frozen and delivered to the laboratory for complete helminthological dissection.All the trematodes found were collected and fixed in 70° alcohol, and then they were treated with carmine dye and identified.The collected trematodes were identified using classical monographs and key guides McDonald, 1961;Bykhovskaya-Pavlovskaya, 1962;Gaevskaya et al. 1975;Smogorjevskaya, 1976;Ginetsinskaya T.A., Dobrovolsky, 1978 etc.).Faunistic similarity of the little grebe trematodes of various water bodies was assessed by the Czekanowski-Soerensen index (Czekanowski, 1913;Soerensen, 1948).

Results
During the study, 12 trematode species were discovered in the little grebe.In systematic list, each species is provided with the following data: collecting localities, extensity (% of infected birds) and intensity (individuals per bird) of invasion, localization in the host body, and a brief information on species biology.
Localization: subcutaneous fat tissue and connective tissue, esophagus and trachea, fascia of the neck and head muscles.
Definitive hosts are birds of the Falconiformes order; mesocercaria localizes in the tissues of amphibians, metacercariae -in different tissues of the waterfowls (Lunaschi, Drago, 2009).
The 12 trematode species found in the examined grebes belong to one order, seven families and eight genera.Of these only three species -Petasiger megacantha, Echinochasmus coaxatus, and E. dietzevi, are specific grebe parasites, the rest infect various water birds.Nine trematode species of our collection occurred only in the gut, one species was found in the liver bile-duct and in the gut, one species in kidneys, and the one in subcutaneous fat and connective tissues, esophagus, trachea, neck and head muscles' fascia.Out of all the trematodes found, only Strigea falconis uses water birds as intermediate hosts.Its cercaria penetrates actively into the bird's body and transforms into metacercaria.The definitive hosts are predator birds of the Falconiformes order.For the other trematode species, water birds are definitive hosts; they are infected via ingestion of fishes, frogs and/or aquatic invertebrates As the grebe is fish-eating bird, 6 species (Patagifer bilobus, Petasiger megacantha, Mesorchis pseudoechinatus, Cryptocotyle concavum, Metorchis intermedius, Hysteromorpha triloba) of 12 species trematodes that found in it, namely the half, parasites in the fish in metacercarial stage and infect birds when they feed on a fish.
Species richness of the trematode fauna depends of environmental conditions of the water body and diversity of its flora and fauna, which created favorable conditions for all members of the parasite life cycle.The three water bodies studied, the Devechi Firthhe, Small Gizilagach Bay and the Kura River delta are the richest in mollusk, fish and bird fauna.Each of them hosted five trematode species.Four species were recorded form the Lower Kura and the Mingechevir Reservoir, three species from the Absheron Peninsula and the Varvara Reservoir, two species from the Middle Kura, and one species from the Lower Araz (Table 1).Comparison of the little grebe trematode faunas of the studied water bodies showed that it includes the same species in the Devechi Firth and the Kura River delta (Kcz-s=100%).Similarity indices were also high in the pairs Small Gizilagach Bay / Devechi Firth, Small Gizilagach Bay / Kura River Delta -66.7% each; Lower Kura River / Small Gizilagach Bay -51.1%, and Middle Kura River / Lower Kura River -50.0%.The closely located Mingechevir and Varvara reservoirs are inhabited be one population of the little grebe.It is isolated from the populations of other water bodies and has no trematode parasites in common with them.On the contrary, similarity index of the trematode species composition in the little grebes of the two reservoirs amounts for 75.5%.Therefore, faunistic similarity of the trematodes depends on the distance between the water bodies and the similarity of their living conditions.
In the previous article (Mahmudova, Ibrahimov, 2020), we divided all the waterfowl trematode species of Azerbaijan into three groups: northern, southern and ubiquitous, in accordance with the division proposed by V.A. Dogel (1949), M.M. Belopol'skaya (1966), andA.A. Smogorzhevskaya (1976).The first group can infect birds only in the northern part of their range during the nesting period, the second group infects them only in the south during wintering, and the third one is able to infect birds throughout their range.Of the trematodes recorded in our study, seven species (Petasiger megacantha, P. skrjabini, Echinochasmus coaxatus, E. dietzevi, Cryptocotyle concavum, Metorchis intermedius, Eucotyle cohni) belong to the northern group, while five species (Patagifer bilobus, Echinochasmus mordax, Mesorchis pseudoechinatus, Strigea falconis, Hysteromorpha triloba) are ubiquitous.The southern species were absent.The noticeable predominance of the members of the northern trematode group and the absence of southern ones, apparently, should be explained by the prevailing of the birds of northern grebe population in Azerbaijan, which do not fly into wintering areas of southern populations and therefore they are not available for the southern species of trematodes.
Of the trematodes found in the little grebe, only Strigea falconis is the causative agent of bird diseases.Its metacercariae are localized in various tissues and infect wild and domestic birds.That results in birds´ weakening and a significant decrease in the quality of their meat (Krone, Streich, 2008;Drago et al., 2014;Olinda et al.2015).

Conclusion
Parasitological studies of the 94 little grebe individuals at nine water bodies of Azerbaijan revealed 12 trematode species.The research was conducted in 1998-2019.Only three species are specific grebe parasites.Differences of the grebe trematode faunas of various water bodies depended on the distance between them and similarity of their living conditions.Seven species in the studied trematode fauna belong to the northern group of helminths, while the five ones are ubiquitous.