This study is devoted to the investigation of Azygia (Digenea: Azygiidae) species diversity using classical morphological, recent molecular tools (28S rRNA and cox1 mtDNA for genetic-based inference) and robust statistical techniques (Principal component analysis, PCA). The analysis revealed that the genus Azygia included four valid species: A. lucii, A. longa, A. hwangtsiyui, and A. sibirica n. sp. The distribution of the type species A. lucii was confirmed in the largest Russian rivers: the Volga and the Ob. The worms isolated from Perccottus glenii were determined as the Chinese species A. hwangtsiyui, according to the genetic data for the cox1 mtDNA gene, at 1.32–1.56%. The new species, Azygia sibirica n. sp, was described from Esox lucius in the Ob River and differentiated from the type species A. lucii by the smaller ovary, testes and prostatic sac, wider body, very narrow pharyngeal lumen and form of anterior margin of ovary. In addition, multivariate analysis and three methods for species delimitation (ABGD, GMYC, bPTP) showed the subdivision of A. lucii and A. sibirica n. sp. into two separate groups, one from the Volga River and another from the Ob River, respectively. To conclude, A. lucii infects Esox lucius in the western (European part of Russia, the Volga River basin), and northern (Western Siberia, the Ob River basin) parts of Russia; A. sibirica n. sp. has also been found to infect Esox lucius in the Ob River, while A. hwangtsiyui infects Perccottus glenii in the South of the Russian Far East (the Artymovka River basin).

Using four types of markers, the genetic variability of sable and pine marten inhabiting Western Siberia was examined. Izoenzyme and restriction endonuclease analysis of the mtDNA cytochrome b gene...

Based on the polymorphism of multilocus DNA markers (inter simple sequence repeat (ISSR)), we assessed the level of genetic variability and differentiation of populations of two invasive species, the Amur sleeper ( Percottus glenii ) and its specific parasite, Nippotaenia mogurndae , from five reservoirs in the acquired part of the range, the Irtysh River basin, Western Siberia. We revealed a high genetic polymorphism of neutral DNA markers in P. glenii . In general, the proportion of polymorphic loci was 92%, the average heterozygosity was 0.32. These parameters were lower in particular populations of P. glenii and varied within 53–74% and 0.20–0.23, respectively. The interpopulation component accounted for approximately 35% of the variability ( G _ST = 0.35). In N. mogurndae , polymorphism was 73.7%, heterozygosity was 0.18, varying within 18–45% and 0.06–0.15, depending on the population. The level of genetic differentiation of N. mogurndae ( G _ST = 0.38) was similar to that of P. glenii , which indicates that the processes of genetic differentiation of the parasite and the host are synchronous. Polymorphism and genetic distances of the parasite were lower than those of the host. The population genetic structure of P. glenii was partially consistent with the structure of the hydrographic network, in contrast to N. mogurndae . The data obtained indicate that during dispersal, no significant reduction in genetic polymorphism occurred in the Amur sleeper, and over several decades a population-genetic structure characteristic of this species in the native range was formed in the acquired part of the range.

Data are presented on genetic subdivision of populations of roach Rutilus rutilus lacustris, ide Leuciscus idus, and dace L. leuciscus baicalensis living in rivers of West Siberia. These fish species have comparable levels of variation of allozyme loci and similar populational structure which well agrees with geography of the river network of the Ob-Irtysh basin. The populational differentiation is more expressed in ide than in roach and dace.

The composition of helminths and infestation indices of two frog species of living in Western Siberia (Rana arvalis (n = 1082) and Rana amurensis (n = 33)) have been studied. Nine helminth species, including four nematodes and five trematodes, have been found. The following species were dominant and infected both frog species: nematodes Rhabdias bufonis, Oswaldocruzia filiformis, and Cosmocerca ornata and trematodes Haplometra cylindracea. The moor frog also hosted Dolichosaccus rastellus, Opisthioglyphe ranae, Pharingostomum cordatum (larvae), Parastrigea robusta (larvae), and Neyraplectana schneideri. The moor frog was characterized by higher species richness and diversity of helminths than the Siberian tree frog. The overall rates of helminth infestation have been the same in the moor frog and the Siberian tree frog. The invasion extensity was 85–100%; the index of abundance was 5.2–27.5. Differences in infestation rates of certain species by helminths were due to the biological peculiarities of the frog species.