[Biological and ecological background of nematode fauna structure formation in the alimentary tracts of wild Anatinae ducks in north-western Poland].

The study involved a total of 250 wild ducks representing 17 species of three ecologically different tribes: the Anatini (113 individuals), the Aythyini (71), and the Mergini (66). The ducks, obtained mainly from fishermen and hunters, were examined for the presence of parasites, using the generally accepted methods. Analyses of nematode assemblage structure were conducted with methods described in the literature. In addition, significance of differences in intensity of infestation was determined in relation to the hosts' age and sex as grouping variables. Significance of differences in infestation prevalence was tested with the Pearson Chi2 test or its modifications (V-square test, Chi2 test with Yates' correction, and the exact Fisher's test), while the Mann-Whitney U test was applied to infestation intensity and relative density. Similarity coefficients were ordered using the cluster analysis module of the STATISTICA 6.0 computer software; Ward's algorithm was used for grouping, Euclidean distance being applied as the similarity measure. The ducks examined were found to host a highly diverse nematode assemblage, consisting of a total of 22 species representing the following 7 families: Amidostomatidae, Anisakidae, Ascarididae, Tetrameridae, Acuariidae, Dioctophymatidae, and Capillariidae, the core of the assemblage being formed by the following 7 species: Amidostomoides acutum, A. monodon, A. petrovi, Tetrameres fissispina, Echinuria uncinata, Eucoleus contortus, and Capillaria anatis. The assemblage of parasitic nematodes in the ducks examined was found to be characterized by a high organ specificity, as the parasites selected mainly the gizzard and proventriculus as their microhabitats (10 and 8 typical species, respectively) and firmly avoided the duodenum and cloaca. Individual parasite species were observed to show a clear preference with respect to location in the host's alimentary tract, which means that, for a distinct majority of the parasitic species, typical sites could be identified. No significant effects of host's age and sex on nematode infestation parameters could be revealed, although - in certain species - those variables proved of a key importance for their specificity. The nematodes showing a distinct preference towards young birds include E. uncinata and Ingliseria cirrohamata, a still higher specificity being displayed by T fissispina and A. petrovi (selectively parasitising young females) and C. anatis (selective with respect to young males). The species which were more frequently recorded in the ducks aged two years and more, particularly in the adult males, include A. monodon and A. acutum. A clear relationship between the ecology of a host and the structure of its parasitic nematode assemblage was observed. Each of the tribes was distinct in the specific nematofauna of its members, each nematofauna possessing its own well-expressed core. The nematofauna of swimming ducks (Anatini) consisted of 11 species, the core being formed by A. acutum, E. uncinata, T fissispina, and E. contortus. The diving ducks (Aythyini) were found to host 8 nematode species, the core being formed by A. petrovi, T. fissispina, and C. anatis. The nematofauna of the predacious Mergini was found to consist of as many as 17 species, although one of them (A. monodon) was a distinct dominant. The nematode fauna of those birds showed also a relatively high proportion of T. fissispina, the most polyxenic nematode, recorded in 10 host species of all the tribes studied. Although the problem of habitat partitioning between various components of a nematode assemblage could not be unambiguously resolved, it was evident that cases of co-occurrence involved mainly co-invasions at different sections of the alimentary tract of the same host, the strongest relations being found for those species that formed the core of a nematode assemblage. Co-invasions affecting a host's organ concerned almost exclusively representatives of the families Amidostomatidae and Acuariidae in the gizzard and those of the Tetrameridae and Acuariidae in the proventriculus. The similarities between nematofaunas of the ducks studied are only weakly related to the systematic position of the respective ducks; much stronger relationships with ecological characteristics (mainly food type and feeding habits) were revealed. It seems that this is why the nematofauna of Common Goldeneye is much more similar to that of the Aythyini than to that of the Mergini to which the species is taxonomically assigned.