Explore the vast range of titles available.

Otolith abnormalities and bilateral asymmetry are analyzed in five reproductively isolated forms and natural F1 hybrids between the forms in Arctic charr Salvelinus alpinus complex from lakes Lama and Kapchuk (Norilo-Pyasinskaya water system, Taimyr). Otolith abnormalities are associated with the partial replacement of aragonite (the usual otolithic polymorph of CaCO 3 ) by vaterite (another less stable crystalline modification of CaCO 3 ) and their unusual shape. The abnormalities are observed in 11.9% of the specimens and may be induced by technogenic pollution from Nornickel, the world’s largest manufacturer of palladium, nickel, and platinum. The assessment of bilateral asymmetry based on otolith measurements and shape indices does not indicate notable differences in this parameter between the charr forms. However, the shapes of the left and right otoliths described by wavelet analysis are significantly different in two groups: a form of Lake Kapchuk designated as the main form and F1 hybrids. The differentiation of the forms is evaluated using wavelet and linear discriminant analyses of otolith shape. The difference in the topologies of two dendrograms constructed based on the shapes of the left and right otoliths obtained from the same specimens can be explained by the occurrence of bilateral asymmetry.

Growth, peculiarities and anomalies of the ossification and development of skeletal elements, as well as body proportions and meristic characters of laboratory-reared larvae and fry of two lacustrine dwarf forms of Arctic charr Salvelinus alpinus complex from lakes Tokko and Bol’shoe Leprindo (Transbaikalia) were studied. Retardations of the formation of blood cells, anomalies of morpho- and osteogenesis, and increased mortality of unhatched embryos, free embryos and prelarvae of reciprocal hybrids were revealed. Initial characteristics of prelarvae, linear growth, rate of osteogenesis, body proportions, and colouration of hybrid individuals matched matroclinal developmental pattern. Heterochrony of the ossification of vertebral centra was revealed in prelarvae of the hybrid between females from Lake Tokko and males of the deep-water form from Lake Bol’shoe Leprindo. Their ossification was displaced to an earlier stage in the typical ossification and differentiation sequence of skull bones and fin rays, which indicates the presence of respective regulator in parental genome. Such effect was not observed in reciprocal hybrid; however, it demonstrated earlier ossification of predorsalia than the pure form from Lake Bol’shoe Leprindo. The formation of morphological features in the ontogeny of hybrid larvae and juveniles as compared with parental forms was traced. All lethal anomalies of reciprocal hybrids and non-lethal anomalies influencing their viability as well as accelerated use of yolk by hybrids between the females from Lake Bol’shoe Leprindo and males from Lake Tokko, which resulted in mass mortality of prelarvae and weak development of the skeleton of early larvae are considered as the elements of post-zygotic reproductive isolation between pure forms of gen. Salvelinus from the two lakes. This isolation is obviously incomplete since part of hybrid individuals developed normally, though their fertility remains unknown.

The results of the study of growth, ossification sequence and peculiarities of the development of skeletal elements, body proportions and meristic characters of laboratory-reared larvae and fry of two dwarf forms of Arctic charr Salvelinus alpinus сomplex spawning at the shore slope (Lake Tokko) and in the profundal zone (Lake Bol’shoe Leprindo) (Transbaikalia) are presented. Charr from Lake Bol’shoe Leprindo demonstrated slower rates of growth and morphogenesis, retardation of the ossification of their predorsal bones series with its displacement from larval to juvenile period of the ontogeny, but the acceleration of the development of the vertebral column. High mortality of pre-larvae of charr from this lake connected with the transfer to exogenous feeding was observed. For the first time the problem of the reorganization of early ontogeny of charr of the genus Salvelinus in connection with the colonization of deepwater habitat is discussed. In larvae of charr from Lake Tokko, the ossification of vertebral centra was often accompanied by the formation of anomalous bony structures in the notochord. The phenomenon of the penetration of skeletogenic cells into the notochord, which has been described in hybrids of sympatric charr forms, was found in a pure charr form for the first time. The development of characteristic morphological features of the two charr forms in the ontogeny was traced. Differences in body proportions between their fry corresponding to those between adult fish were revealed.

Within the Arctic charr complex ( Salvelinus alpinus complex), many different populations and forms with disputable origin and systematic status have been described. Some of them, such as the charr from Lake Cherechen’ (middle Kolyma River basin), combine characters of different phylogenetic groups, representing a possible consequence of former hybridization. The data on 32 allozyme loci and on nucleotide sequences of 501-bp fragments of the mtDNA control region as well as of 899-bp fragments of exon 2 of the RAG1 gene were used for the analysis of the origin of Lake Cherechen’ charr and their phylogenetic relationships with other representatives of the Arctic charr lineage. As was shown previously, the dwarf and large forms of charr from this lake are morphologically similar to other charr populations from the upper Kolyma River, but bear the mtDNA haplotype of northern Dolly Varden Salvelinus malma malma , not of Taranets charr Salvelinus alpinus taranetzi . The analysis of the allozymes and RAG1 gene confirms the affinity of the Lake Cherechen’ charr to the Arctic charr lineage, but it is insufficient to unambiguously attribute them to the Eurasian or Taranets group. The presence of mtDNA of northern Dolly Varden in Lake Cherechen’ Arctic charr and the replacement of their native mtDNA are the result of the introgressive hybridization with S. m. malma . An alternative explanation connected with incomplete lineage sorting seems highly improbable. Our study confirms a postglacial secondary contact of the representatives of different phylogenetic groups of the S. alpinus - S. malma species complex in the Kolyma basin and in the area from Taimyr to Chukotka. It also indicates the need for more thorough analysis of the morphological and genetic diversity of charr from this region as well as caution in taxonomic decisions.

In order to study the distribution of phylogenetic mtDNA lineages of Arctic charr Salvelinus alpinus in their contact zones in the north of East Siberia we analyzed nucleotide sequences of mtDNA control region of charr from 10 Arctic populations in the area from the Yenisei to the Lena. At the Putorana plateau, haplotypes of Atlantic and Siberian subgroups of Eurasian group were recorded, in the Khatanga River basin, haplotypes of Atlantic subgroup, in the Lena River delta, haplotypes of Siberian subgroup and of Bering group were observed. Some Siberian haplotypes found at the Putorana and in the Lena delta, have been earlier registered in other regions of East Siberia. New findings, along with published materials allow to specify the ranges of these three phylogenetic lineages and the margins of their contact zones; they also evidence wide sympatry of Atlantic and Siberian haplotypes in Taimyr water bodies and support close relationship of charr of Siberian subgroup from all main areas of their distribution.

The complete mitochondrial genome was sequenced in two individuals of Taranetz charr Salvelinus taranetzi. The genome sequences are 16,654  bp in size, and the gene arrangement, composition, and size are very similar to the charr genomes published previously. The difference between the two genomes studied is low, 0.05%. The present study confirms the independent taxonomic status of S. taranetzi within the genus Salvelinus. The level of sequence divergence between S. taranetzi and Salvelinus alpinus inferred from the complete mitochondrial genomes is relatively low (1.1%), indicating recent divergence of the species.

In Lake Amut (the Verkhnyaya Angara drainage basin) the third population of Arctic charr Salvelinus alpinus (L.) in Baikal basin was found, a presumed invader from the Lena basin; besides, one more representative of Lena ichthyofauna was recorded—sculpin Cottus cf. poecilopus Heckel. This lake is situated close to the divide with the Pravaya Mama River (the Vitim basin), not far from its main channel. The relief structure of the watershed area, in which Lake Amut is located, indicates high probability of the invasion of Lena species into Baikal basin at this place. Data on morphology, age, growth and diet of Arctic charr from Lake Amut are presented and compared with the data on other charr from Baikal basin. New records are discussed in the context of Pleistocene paleogeography of the Baikal region relevant to the history of its fish fauna formation.

Based on data from 1997–2019, morphology, growth, feeding, reproduction and early development of Arctic charr from Lake Tokko (Olekma basin, northern Transbaikalia) were studied. Three charr forms, large, small and dwarf differing in growth rate were recorded in the lake. During the last years, the large form disappeared, the small form became rare and the dwarf form became highly abundant; the proportion of old small and dwarf charr sharply decreased. The dwarf form differs in morphology from the small and large forms, which are morphologically similar. In the summer period of 1997–2001, the large form fed on fish, the small form fed mainly on amphibious insects (chironomid pupae), and the dwarf form fed on amphibious insects and benthos. Presently the small form transited to piscivorous and the dwarf form to predominantly planktivorous feeding. The dwarf form spawns from late July to mid-August at stony sites of underwater shore slope when water temperature is 5.0–6.5°С; laid eggs develop till late November–early December at water temperature decreasing to 3.0–3.5°С. According to data needing verification, the small form spawns in late autumn, but some individuals spawn in summer at the same time as the dwarf form. The results suggest substantial, though incomplete reproductive isolation between the dwarf and the small forms. It is supposed that nowadays the degree of their introgressive hybridization has increased following anthropogenic changes in population structure.

In the system of lakes Bol’shoe Leprindo and Maloe Leprindo (Lena basin, Transbaikalia), spawning of two isolated populations of the dwarf form of Arctic charr Salvelinus alpinus was studied. The results supplemented with the data about the exterminated large form from these lakes, demonstrate a unique combination of sympatric and parapatric charr forms with autumn (large form), summer (dwarf form, Bol’shoe Leprindo) and first recorded in Russia winter-spring (dwarf form, Maloe Leprindo) spawning peaks. In both lakes, the dwarf form spawns in the profundal zone at silty bottom at the depth 25–58 m: in Bol’shoe Leprindo, from late June to October with peak in July-August when water temperature is 5–6°С, in Maloe Leprindo from January to July, with peak in January–March when temperature is 2.5–3.0°С. Eggs laid in July–August in Bol’shoe Leprindo develop for 3.0–3.5 months, eggs laid in January–March in Maloe Leprindo, for about 4.0–4.5 month; in both lakes they are actively consumed by burbot Lota lota . Due to smaller egg size the dwarf form has twice as high individual relative fecundity as the large form, which compensates for high egg mortality. It is supposed that the differences in spawning strategies were formed as the result of outcompeting of the dwarf form by the large form from the littoral to the profundal zone, where perennial low temperature favoured the prolongation and displacement of their spawning time. These differences determined reproductive isolation and genetic divergence between three charr populations.

We contrast the genetic consequences of allopatric and sympatric divergence from the littoral spawning Arctic charr morph from Lake Fjellfroesvatn. The littoral spawning Arctic charr has sympatrically diverged into a natural profundal adapted morph and via a recent (1930) translocation of about 40 adult Arctic charr established a new allopatric population in a nearby lake (Takvatn). The sympatric morph-pair in Fjellfroesvatn was more genetically differentiated (F sub(ST) = 0.121), the derived profundal morph had higher genetic variation (He = 0.740 plus or minus 0.220; N sub(PAR) = 4.87), and had a higher proportion of linkage disequilibrium among loci, than the Takvatn charr derived in allopatry (F sub(ST) = 0.066; H e = 0.584 plus or minus 0.193; N sub(PAR) = 0.29). The genetic differentiation in allopatry supports a scenario of rapid population expansion, despite genetic founder effects, whereas the genetic differentiation found in the sympatric morph-pair suggests that this divergence is older and supports a scenario of divergence under ongoing gene flow. We suggest that the differences between the two types of divergence may originate from temporal effects and differences in life histories between the two derived populations along with specific factors related to the initial stages of the divergence.