S. S. Alekseyev

Diversification, Sympatric Speciation, and Trophic Polymorphism of Arctic Charr, Salvelinus Alpinus Complex, in Transbaikalia

In northern Transbaikalia, independently evolving landlocked populations of Arctic charr are found in mountain lakes. To assess the diversity of charr in this region, speciation modes involved in the evolution of charr forms, and the role of trophic polymorphism in their divergence, we studied the morphology and feeding of dwarf, small, and large forms of Arctic charr from a number of Transbaikalian lakes. Meristic data on charr from five lakes support the earlier conclusion that the three forms do not represent separate lineages but have independently diverged in sympatry in each of the lakes. In 10 lakes, the dwarf form showed varying degrees of differentiation from normal (small and large) charr in meristic characters (up to morphologically distinct and presumably reproductively isolated groupings), which is viewed as various levels of sympatric divergence. Indexes of gill raker length in fish from 20 lakes vary among populations of both dwarf and normal charr, with forms having short and long rakers being sympatric in some of these lakes. However, the index can be used only for comparing charr of different forms up to about 32 cm fork length (FL) because it is strongly negatively correlated with size in larger fish. The study of charr diets in 21 lakes indicates that large charr are piscivorous whereas dwarf and small charr feed on a wide range of invertebrates, partitioning these resources in different ways. Planktivores, including very specialized ones, and non-planktivores (benthic feeders, insectivores) can be identified within the small and dwarf forms. The proportion of plankton in the diets of dwarf and small charr is positively correlated with the number and length of gill rakers while the proportion of benthos is negatively correlated. Allopatric planktivorous and non-planktivorous small charr differ in body proportions; parallel emergence of such morphotypes in different parts of the range is a characteristic feature of the Salvelinus alpinus complex.

Phylogeography and sympatric differentiation of the Arctic charr Salvelinus alpinus (L.) complex in Siberia as revealed by mtDNA sequence analysis.

Sequence variation in the mtDNA control region of Arctic charr Salvelinus alpinus and Dolly Varden Salvelinus malma from 56 Siberian and North American populations was analysed to assess their phylogeographic relationships and the origins of sympatric forms. Phylogenetic trees confirm the integrity of phylogroups reported in previous mtDNA studies except that the Siberian group does not separate as a single cluster. Haplotype network analysis indicates the proximity of Siberian and Atlantic haplotypes. These are considered as one Eurasian group represented by the Atlantic, east Siberian (interior Siberia including Transbaikalia, Taimyr) and Eurosiberian (Finland, Spitsbergen, Taimyr) sub-groups. Salvelinus alpinus with presumably introgressed Bering group (malma) haplotypes were found along eastern Siberian coasts up to the Olenek Bay and the Lena Delta region, where they overlap with the Eurasian group and in the easternmost interior region. It is proposed that Siberia was colonized by S. alpinus in two stages: from the west by the Eurasian group and later from the east by the Bering group. The high diversity of Eurasian group haplotypes in Siberia indicates its earlier colonization by S. alpinus as compared with the European Alps. This colonization was rapid, proceeded from a diverse gene pool, and was followed by differential survival of ancestral mtDNA lineages in different basins and regions, and local mutational events in isolated populations. The results presented here support a northern origin of Transbaikalian S. alpinus, the dispersion of S. alpinus to the Lake Baikal Basin from the Lena Basin, segregation of S. alpinus between Lena tributaries and their restricted migration over the divides between sub-basins. These results also support sympatric origin of intralacustrine forms of S. alpinus.

The second population of Arctic charr Salvelinus alpinus complex (Salmoniformes, Salmonidae) in the Lake Baikal basin, the highest mountain charr population in Russia

We report the finding of the second population of Arctic charr in Lake Baikal basin, in a nameless lake in the Barguzin mountain range in the outlet of the Svetlaya River. The lake is situated at an altitude of 1766 m above sea level; this is the highest lake inhabited by this species in the territory of Russia. Two abundant charr forms, dwarf and small, were recorded in the lake; data on their ecology, morphology, age composition, growth, and microsatellite variation are presented. Both forms feed mainly on zooplankton, though neither has pronounced morphological traits characteristic of specialized plankton-feeders. Dwarf and small charrs are rather close in meristic characters and in the length of gill rakers, but differ substantially in allele frequencies and allele diversity at the microsatellite loci, which is indicative of a high degree of reproductive isolation between them. The discovered population is the only one among Transbaikalian charr populations, that, due to its remoteness, has not been affected by man. For that reason, it can be considered as an etalon of an undisturbed natural charr population. The lake and its surroundings should receive official protected status.

The evolutionary history of sharp- and blunt-snouted lenok (Brachymystax lenok (Pallas, 1773)) and its implications for the paleo-hydrological history of Siberia.

BackgroundBroad-scale phylogeographic studies of freshwater organisms provide not only an invaluable framework for understanding the evolutionary history of species, but also a genetic imprint of the paleo-hydrological dynamics stemming from climatic change. Few such studies have been carried out in Siberia, a vast region over which the extent of Pleistocene glaciation is still disputed. Brachymystax lenok is a salmonid fish distributed throughout Siberia, exhibiting two forms hypothesized to have undergone extensive range expansion, genetic exchange, and multiple speciation. A comprehensive phylogeographic investigation should clarify these hypotheses as well as provide insights on Siberias paleo-hydrological stability.ResultsMolecular-sequence (mtDNA) based phylogenetic and morphological analysis of Brachymystax throughout Siberia support that sharp- and blunt-snouted lenok are independent evolutionary lineages, with the majority of their variation distributed among major river basins. Their evolutionary independence was further supported through the analysis of 11 microsatellite loci in three areas of sympatry, which revealed little to no evidence of introgression. Phylogeographic structure reflects climatic limitations, especially for blunt-snouted lenok above 56° N during one or more glacial maxima. Presumed glacial refugia as well as interbasin exchange were not congruent for the two lineages, perhaps reflecting differing dispersal abilities and response to climatic change. Inferred demographic expansions were dated earlier than the Last Glacial Maximum (LGM). Evidence for repeated trans-basin exchange was especially clear between the Amur and Lena catchments. Divergence of sharp-snouted lenok in the Selenga-Baikal catchment may correspond to the isolation of Lake Baikal in the mid-Pleistocene, while older isolation events are apparent for blunt-snouted lenok in the extreme east and sharp-snouted lenok in the extreme west of their respective distributions.ConclusionSharp- and blunt-snouted lenok have apparently undergone a long, independent, and demographically dynamic evolutionary history in Siberia, supporting their recognition as two good biological species. Considering the timing and extent of expansions and trans-basin dispersal, it is doubtful that these historical dynamics could have been generated without major rearrangements in the paleo-hydrological network, stemming from the formation and melting of large-scale glacial complexes much older than the LGM.

Genetic Differentiation of Arctic Charr Salvelinus alpinus Complex from Transbaikalia Revealed by Microsatellite Markers

Variation at eight microsatellite loci was studied in Arctic charr Salvelinus alpinus complex from five Transbaikalian mountain lakes. Samples from three lakes included two sympatric charr forms (dwarf and small) differing in trophic specialization, morphology and life cycle parameters. Sympatric forms were genetically closer to each other than to charr from other lakes which evidences their independent origin in each of these lakes as the result of sympatric speciation. In each lake, gene pools of sympatric forms were segregated to a different degree (estimates of FST varying from 0.030–0.184 and those of ρST varying from 0.119–0.359). Hierarchical analysis of allelic frequencies variance (AMOVA) in Arctic charr from Lake Baikal, the Vitim, and the Olekma basins showed that variation among and within these basins accounted for 19.5% of the interpopulational variance each. In the AMOVA design, investigating differences among sympatric forms in three lakes these differences accounted for 7.1% of the total variance.

Three sympatric forms of Arctic charr Salvelinus alpinus complex (Salmoniformes, Salmonidae) from Lake Kamkanda, Northern Transbaikalia

We studied morphology, size and age structure, growth, feeding, and variation at microsatellite loci of three forms of Arctic charr Salvelinus alpinus complex (dwarf, small, large) from mountain Lake Kamkanda in River Olekma basin, northern Transbaikalia. The forms differ in meristic and morphometric characters, external appearance and size. The small form distinctly differs from the dwarf and large forms in higher number and length of gill rakers. The forms differ in growth rate; however, differences in growth between the dwarf and the small forms are not as large as between sympatric dwarf and small charr from other Transbaikalian lakes. The large form is heterogeneous in growth rate. The small form matures one year earlier than the dwarf form and has a shorter life span. The dwarf form is a benthophage, the small form is a planktophage, and the large form is a predator. The dwarf form spawns in September, while the small form spawns in November-December, and there is no overlap in their spawning time. The three forms have clear genetic differences, which support their reproductive isolation. It is assumed that the three forms of Arctic charr originated within Lake Kamkanda on the basis of trophic polymorphism and spawning time displacement and attained a high degree of morphological and genetic divergence.

Late ontogeny growth acceleration and size form transformations in Transbaikalian Arctic charr, Salvelinus alpinus complex: evidence from fin ray cross section growth layers

In some polymorphic populations of Arctic charr in Transbaikalia, an individual can transform from a smaller to larger size form during their lifetime as a result of accelerated growth that follows a period of slow growth and reproduction as a small size form. Alternating periods of slow and fast growth are reflected in growth layer patterns visible in fin ray cross sections. Stained microtome fin ray cross sections were used to reveal the incidence of transformations from one form to another. Data were collected from 14 northern Transbaikalian lakes containing two or three sympatric Arctic charr forms (‘dwarf’, ‘small’, and ‘large’) exhibiting varying levels of morphological separation. Individuals recruited from the dwarf or small form were found in varying proportions among the small and/or large form in 12 lakes. Small or large form charr that grew without noticeable acceleration to the adult size typical of the form or experienced accelerated growth as juveniles prior to maturation were also observed. There were no transformations between sympatric forms that differed in the length and number of gill rakers and in some other meristic characters. Results indicate that in the region under study, transformations of sympatric Arctic charr size forms are a widespread, but not a ubiquitous, phenomenon. Such transformations reflect the plasticity of the developmental channels of the forms. In the course of intra-lacustrine form divergence and genetic differentiation, the frequency of the observed transformations decreases to zero.

Differentiation of Sympatric Arctic Char Morphotypes Using Major Histocompatibility Class II Genes

AbstractArctic Char Salvelinus alpinus have colonized northern postglacial lakes within the last few thousand years. Divergent populations have adapted to thrive in the prevailing oligotrophic environments and thus have developed morphotypes with different ecological behaviors. The morphotypes usually differ in size, morphology, coloration, feeding ecology, and/or habitat occupancy. Although morphotypes that have very divergent spawning seasons should become genetically segregated, genetic differentiation, in most cases, has been weak. Thus, results to date have suggested that Arctic Char morphotype separation has been driven largely by the environmentally mediated phenotypic plasticity of the species, with differentiation between morphotypes having commenced too recently to generate substantial genetic drift. Here we used the major histocompatibility (MH) class II genes in an attempt to isolate sympatric Arctic Char morphotypes known to be ecologically differentiated. These morphotypes are from postglaci...

Global major histocompatibility Class II β (mh-IIβ)-polymorphism in Arctic charr Salvelinus alpinus

This study explored the use of the gene encoding the β subunit of the major histocompatibility (MH) receptor as a population marker in Arctic charr Salvelinus alpinus. The use of this polymorphic marker allowed differentiation of the S. alpinus lineages previously defined using mitochondrial DNA (mtDNA) but also allowed differentiation between the populations studied within those lineages. The majority of the variation observed here occurred prior to the last glaciation event. Nevertheless, all S. alpinus populations were differentiated using both MH Class II β (mh-IIβ) sequences and allelic frequencies. The fact that all the populations studied presented high rates of non-synonymous: synonymous substitutions and high levels of interpopulation variation, suggested mh-IIβ as an ideal marker to assess differentiation among S. alpinus populations in ways that may represent divergence both by genetic drift and natural adaptation to the local environment.

On the origin and phylogenetic position of Arctic charr (Salvelinus alpinus complex, Salmonidae) from Lake Cherechen’ (middle Kolyma River basin): controversial genetic data

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.