Archive

This review presents modern ideas about the evolution and phylogeny of a group of obligate intracellular eukaryotic parasites - the Microsporidia. In the process of adaptation to the intracellular parasitism, the genome and functional apparatus of these organisms was significantly reduced and modified. The systematic position of this group remained unclear for a long time, and it was not known for certain how the evolution of microsporidia occurred, when and how they acquired their unique adaptations to the parasitic lifestyle. A real breakthrough in the study of the evolution of microsporidia has been made only in the last few years. The groups that occupy the position closest to microsporidia on the tree of life were found and described: Cryptomycota (Rozellida) and Aphelida. Sequencing of the genomes of representatives of these groups, which also belong to intracellular parasites, and the first genomic data on the representatives of the basal branches of microsporidia obtained in 2013-2020, made it possible to take a fresh look at the evolution of microsporidia and their closest relatives, to find intermediate forms on the way to adaptation to intracellular parasitism.

Defense reactions of pulmonate molluscs have been actively studied in the last decades, which resulted in the accumulation of abundant data on various aspects of their immune response both at the cellular and the humoral level. Several reviews analyzing this material have recently been published (Adema, Loker, 2015; Pila et al., 2016a; Melillo et al., 2018; Li et al., 2020). However, the last reviews on this subject in Russian were published more than 15 years ago (Ataev, Polevshchikov, 2004; Ataev et al., 2005a, b; Galaktionov, 2005). This review aims to generalize modern ideas about the immune response of pulmonate molluscs and to outline the main problems in this area. It considers defense reactions of the molluscs to various immunization factors, with the focus on the response to trematode invasion. This is due not only to the importance of pulmonates as intermediate hosts of trematodes but also but the possible involvement of these parasites in the development of molluscan immunity.

The structure of the body wall (cuticle, hypoderm, and muscle layer) of the Trichostrongylus tenuis (Mehlis, 1846) (male) nematode from the Trichostrongylidae family, was studied using light and electron microscopy methods at ultrastructural level. It was found that the adult helminth cuticle consists of 8 layers (1 - an outer membrane layer or epicuticle, 2 - outer cortical layer, 3 - inner cortical layer, 4 - homogeneous or middle layer, 5 - outer fibrous, 6 - middle fibrous, 7 - inner fibrous, 8 - basement membrane). Unlike other nematodes, in the homogeneous layer of the T. tenuis cuticle, no dark cuticle struts were detected. The cuticular ridges, which are of diagnostic value, in this nematode are small in size but larger in number than in comparison with other studied species. At the ultrastructural level, the renewal of the cuticle (shedding) of the 4^th larvae stage (male) helminth is gradually traced and described. The cuticular ridges in T. tenuis appear at the last stage of moult, when the old cuticle is completely separated from the new, and not like other similar species, in the early stages. In muscle cells of the T. tenuis nematode, the plasma part is less than contractible. The muscle layer, being larger than the other two layers, is 1.6 times thicker than the cuticle and 9.1 times than the hypodermis.

The lethal effects of metabolic products produced by the symbiotic bacteria Xenorhabdus bovienii from Steinernema feltiae and X. nematophila from S. carpocapsae were tested on Meloidogyne incognita infective juveniles (J2). Treatments had cell titers of 2.5 x 109, 1.25 x 109 and 0.63 x 109 per ml at 20 °C, 23 °C and 26 °C. Exposure periods were 15 hr, 41 hr, 65 hr and 90 hr immediately after autoclaving and at 23°C, and exposure periods of 5 hr, 26 hr, 50 hr and 74 hr after storage for 21 days at 4 °C. The effectiveness of bacterial metabolic products immediately after preparation against M. incognita (J2) depended on the titer of bacterial cells, the temperature of the culture liquid, and the duration of its exposure to nematodes. Nematicidal activity of X. bovienii metabolic products was higher than that of X. nematophila. Mortality of M. incognita J2 was 92-93 % after 90-hr exposure to X. bovienii at 20 °C and cell titers of 2.5 x 109 and 1.25 x 109; also after 65 hr exposure at 23 °C, titer of 2.5 x 109 and 95-99 % at 26 °C and all tested titers. The efficacy of cultural liquid of X. bovienii metabolic products after storage at 4°C for 21 days, after its 50 hr exposure to nematodes at 23 °C and cell titers of 2.5 x 109 and 1.25 x 109 and 74 hr exposure at all tested titers remained high at 97-100 %. The easiest way to control of plant pathogenic nematodes would be metabolic products of symbiotic bacteria of Xenorhabdus. Our results suggest that the active metabolites of symbiotic bacteria need to be identified for possible synthesis and use in the field.

Altai Osmans, united in the genus Oreoleuciscus, are endemic fish of Central Asia. The high plasticity of morphological characters, the ability to sympatric intraspecific diversification, and the evolutionary youth of the group make the situation with the taxonomic structure of the genus Oreoleuciscus extremely difficult, and at the same time facilitate intensive and versatile studies of fish of this genus. The expansion and deepening of knowledge on the taxonomy and ecology of Altai Osmans give a new impetus to parasitological studies of these fish. For the first time, a study of the fauna of parasites of the Altai Osman Oreoleuciscus sp. in Tore-Khol lake' (Ubsunur Hollow, Tuva) was conducted. 16 species of parasites from 8 taxonomic groups were identified: Kinetoplastea - Trypanosoma sp., Cryptobia sp.; Peritrichia - Trichodina intermedia, Trichodinella epizootica; Monogenea - Dactylogyrus phoxini, Gyrodactylus nordmanni; Cestoda - Paradilepis scolecina; Trematoda - Allocreadium transversale, Diplostomum gasterostei, Tylodelphys clavata, T. craniaria; Nematoda - Contracaecum osculatum, Rhabdochona denudata, Pseudocapillaria tomentosa; Acanthocephala - Neoechinorhynchus rutili; Hydrachnidia - Porohalacarus hydrachnoides. All 16 species of parasites are first registered with the host in this lake.

A total of 94 flea species were revealed in the territory of the Eastern Caucasus. 16 of these species are parasites of birds, others are mammal parasites. Among 41 genera of the Caucasian fauna only Caenopsylla, Phaenopsylla, Wagnerina, and Araeopsylla, inhabiting the south of the Caucasus, are absent in the Great Caucasus. Parasites of some birds and carnivorous mammals, insectivores, and rodents are found from lowlands to highlands. A number of species, such as representatives of the genus Callopsylla, are associated with highlands, while other fleas are limited in distribution by semi-desert and steppe foothills and midlands, and are absent in the subalpine and alpine belts. Their main hosts can inhabit a wide range of heights or their distribution is limited.