The fish species Cottus kuznetzovi was described by L.S. Berg in 1903 from the Lena River system. However, two years after its description, Berg synonymized this sculpin with the widely distributed species C. poecilopus Heckel, 1837. It remained a junior synonym until 2009, when this species was redescribed and revalidated. Despite this, some researchers continue to doubt the validity of C. kuznetzovi. The authors obtained new materials from the Arctic region of Eastern Siberia and the upper reaches of the Lena River. This made it possible to apply molecular genetic methods to resolve issues related to the taxonomic status and genetic differentiation of C. kuznetzovi, and also enabled the discovery of this species in new areas. As a result of the analysis of the nucleotide sequences of the mtDNA control region (CR) and the cytochrome b gene (cytb), individuals of the species C. kuznetzovi were identified in the upper reaches of the Lena River, as well as in the Aldan, Indigirka, and Yana river systems. The average p-distance (CR) between different populations was 0.97 ± 0.29%. The presented results indicate a strong genetic isolation of this species from all closely related sculpins. The average p-distances between C. kuznezovi and closely related species of the group “Cottus poecilopus” ranged from 2.50 ± 0.47% to 3.95 ± 0.63% for CR marker, and from 1.50 ± 0.35% to 7.95 ± 0.81% for cytb marker. The validity of this species has been reliably established.

Craniological traits were compared between hatchery-raised and wild-caught juveniles in the Eizenam brown trout Salmo trutta ezenami Berg, 1948 and the Atlantic salmon S. salar Linnaeus, 1758. Six out of ten meristic traits under study were found to differ significantly between the wild and cultivated samples in either species. Among 39 morphometric trait indices, 22 differed significantly between the S. trutta ezenami samples and 14, between the S. salar samples. Differences in meristic traits between the wild and hatchery samples of the same species were greater than differences between the two species. The differences were most likely determined by differences in environmental conditions, although an effect of size variation could not be excluded completely (cultivated fish were somewhat smaller than wild fish). High plasticity of craniological traits should be taken into account when studying the taxonomy and evolution of salmonids.

DNA identification results for certain alien fish species in the Volga-Kama basin are presented. We have revealed different genetic structures among these alien species, which reflect the varying histories of their appearance in the Volga and Kama basins. The observed genetic differentiation of some species is likely related to isolation during transgression and degradation of the Pontic Lake-Sea in the post-Miocene period. The current stage of faunal mixing is associated with the dispersal of hydrobionts beyond their historical ranges through corridors newly formed as a result of human activities. The use of DNA barcoding helped to elucidate the genetic structure of po pulations of several fish species alien to the Volga and Kama. In general, our results did not confirm the advisability of excessively splitting species into the “Azov-Black Sea” and “Caspian” taxa.

The article is a review of systematic studies using osteological characters for reconstructing the phylogeny and constructing the system of bony fishes from the time of Berg’s book Classification of Fishes to the present day. The properties of skeleton related to the nuclear gene induction are reviewed. The induction role of the Hox cluster genes in the sequence of appearance of the anlages of dorsal and anal fin rays and in transformation of the caudal f in structure are discussed. The effects of nuclear genes on the formation of jaws, gill arches, and pectoral fin of f ishes are demonstrated. The conflict between morphologists and molecular biologists regarding the problem of phylogeny reconstruction and systematics is discussed. Using the example of the taxonomic position of the genus Bathylutichthys (Cottoidei), it is shown that information about even one osteological character can fundamentally change the understanding of the phylogeny of the suborder. The conclusion drawn is that morphological and molecular results should be integrated in order to obtain phylogenetic reconstructions and construct a system.

A new parvicursorine theropod, Manipulonyx reshetovi, gen. et sp. nov., is based on a fragmentary skeleton from the Upper Cretaceous (Maastrichtian) Nemegt Formation at Khermeen Tsav, Gobi Desert, Mongolia. The new taxon differs from other parvicursorines in a unique combination of characters. The skeleton of Manipulonyx preserves an articulated and complete forelimb, including rudimentary side fingers, and a complete series of proximal carpals (ulnare, intermedium, and radiale). The proximal carpals were previously unknown for Parvicursorinae. This specimen also shows for the first time the presence of additional dermal ossifications in the carpus, three spikes articulated with (medial and lateral spikes) or attached to (palmar spike) the carpometacarpus. We hypothesize that parvicursorines were egg-eating animals and they used these spikes (covered by a keratinous sheath), as well as rudimentary side fingers, to fix the forelimb on the round and elusive egg surface. After such fixation, the eggshell was punctured by the hypertrophied manual claw. This interpretation is supported by a number of morphofunctional traits of the parvicursorine forelimb discussed in the paper, including the hypertrophied deltopectoral crest of the humerus, keeled sternum, enlarged ectepicondyle of humerus, hypertrophied olecranon of ulna, and lack of the flexor tubercle on the main manual ungual phalanx.

The qualitative and quantitative composition of phytoplankton of the unregulated section of the Ural River and different types of channelized shoulders of the Iriklinsky Reservoir in spring 2016–2022 was analyzed. It is shown that the decrease in the amount of precipitation, the volume of inflow to the reservoir and its level, the volume of discharge and water exchange in 2019–2022 has a significant impact on phytoplankton communities: species richness, number of species in the sample, abundance and biomass, average individual cell mass, and Shannon index decrease. On average for the reservoir during this period, the share of golden algae in the total phytoplankton abundance and biomass increases significantly. The most striking changes in communities occur in the upper section of the reservoir, characterized by shallower depths and proximity to the main river. No increase in the number and proportion of indicator species of α-mesosaprobic and polysaprobic conditions was observed in the composition of the dominant complex of organisms. In case of significant increase in air and water temperature during the low-water period, changes in phytoplankton indicators characteristic of later stages of eutrophication are observed in the upper section, while in the lower section – for earlier stages. During the low-water period, a statistically significant decrease in the saprobic index values was detected. The trophic status of the river waters and different types of the Iriklinskoye Reservoir, determined by phytoplankton biomass, decreases in the lowwater period. The revealed features of oligotrophization cannot be attributed to positive consequences of water availability reduction. Firstly, the reduction of quantitative and qualitative characteristics of phytoplankton indicates the impoverishment of the food base of planktonic consuls and, indirectly, the food base of fish population, and the reduction of biological self-purification potential. Secondly, the scenario of phytoplankton changes in summer and fall seasons of the low-water period can be quite different and demonstrate negative consequences of water availability reduction.

The validity and geographical distribution of the species Plectus frigophilus Kirjanova, 1958 in Antarctica is discussed. Plectus antarcticus de Man, 1904 is common in West Antarctica, and P. frigophilus is common in East Antarctica.

The article puts forward and argues the hypothesis of the emergence of cyclical parthenogenesis in aphids as a consequence of their ancestral habitation in closed strobiloid galls on coniferous trees. The period of gall opening is greatly extended in time, which prevents normal panmixia in the population and creates a selective advantage for parthenogenetic reproduction. Migration of aphids to secondary host plants, on which closed galls never form, parthenogenetic reproduction on these plants, and the subsequent simultaneous return of “remigrants” to the main host plant make it possible to synchronize the development of the bisexual generation and achieve mass panmixia only at the end of the life cycle, which coincides with the end of summer growth shoots or the autumn end of the vegetation period as a whole. Due to the fact that the development of the bisexual generation always necessarily occurs in the second half of the year, when the conditions for aphid feeding on arboreal plants become unfavorable, small size of sexual individuals and their reduced fertility (often only one egg per female), in comparison with parthenogenetic generations of the first half of the year, are understandable. The evolutionary transition of aphids from conifers to angiosperms in the Cretaceous period in parallel meant the possibility of development in more spacious galls accommodating several consecutive parthenogenetic generations, the transition to viviparity and telescopic embryonization, significantly accelerating the change of generations. The loss of ovipositor in Phylloxeridae and in hypothetically descended from them Aphidoidea can be explained by the initial life in galls, where egg laying does not require specialized ovipository organs. The evolutionary transition from oviparity of parthenogenetic generations to viviparity probably occurred in the ancestors of modern Eriosomatidae, as evidenced by the plesiomorphic features of the reproductive biology of the latter.

The paper examines the population dynamics of common species of small mammals in southern Karelia (Sorex araneus L., 1758 and Myodes glareolus Scherber, 1780) based on the results of long-term stationary studies. Small mammals in the study area were captured in the summer and autumn of the period 1966–2014 using standard snap trap lines. At each trapping session, all habitat types were sampled. The dominant species in the small mammal population, like anywhere in Eastern Fennoscandia, were Sorex araneus and Myodes glareolus. Both dominant species live here at the edge of their ranges. As a result of the data analysis of the long-term abundance of these small mammal species, the presence of two time periods (1966–1990 and 1991–2014) was established, differing for each of the species under consideration in the nature of changes in abundance. For both the common shrew and the bank vole in the second period, a change in the nature of population cyclicity was noted, expressed by a change from a tendency toward 3–4-year cycles to chaotic fluctuations. Also, a decrease in the amplitude of population fluctuations was observed for both species. For the bank vole, there was also a decrease in the population level. A discrepancy was noted in the previously existing correlation of the long-term abundance of the background species. The probable reason for such changes is the warming of the climate observed in the north of Eurasia in the 21st century. For peripheral populations of small mammals, endogenous factors regulating numbers come to the fore. This influence is indirect, as warmer winters and springs create more favorable living conditions for animals.

A new effective method for sex determination of immature mouse-like rodents of the hamster family has been used (Cricetidae Fischer, 1817) based on physical impact on the urinary perineal area. The 212 immature specimens of five rodent species was tested: Myodes rutilus Pallas, 1779, M. glareolus (Schreber, 1780), Alexandromys oeconomus Pallas, 1776, Agricola agrestis (Linnaeus, 1761), Myopus schisticolor (Lilljeborg, 1844). Verification of the new method was provided using a control dissection of the studied samples of rodent. The effectiveness of express method of sex determination for under yearling rodent was 88.5–100% among samples of studied species. The effectiveness of morphological characteristics (body weight and length, anogenital distance) was 76.2–93.5% in the sex identification and only for four studied species. The new method was more successful than morphometric methods in sex determination for studied samples of immature M. schisticolor and M. glareolus by 19% and 6.8%, respectively. The close results had been detected for both methods in sex determination of M. rutilus. For sex determination of immature specimens of A. agrestis the morphometric characteristics effectiveness was 4.6% higher compared to the new method. For studied samples of A. oeconomus only the new method of sex determination of an under yearling specimens was effective. The preference in choose of non-anatomical method of sex determination of immature specimens of Cricetidae family is directly depends on the species of study rodent. The new method can be used in studies with vital animals.