Research Article |
Corresponding author: Irina V. Kartavtseva ( irina-kar52@rambler.ru ) Academic editor: Irina Bakloushinskaya
© 2021 Irina V. Kartavtseva, Irina N. Sheremetyeva, Marina V. Pavlenko.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Kartavtseva IV, Sheremetyeva IN, Pavlenko MV (2021) Intraspecies multiple chromosomal variations including rare tandem fusion in the Russian Far Eastern endemic evoron vole Alexandromys evoronensis (Rodentia, Arvicolinae). Comparative Cytogenetics 15(4): 393-411. https://doi.org/10.3897/compcytogen.v15.i4.67112
|
The vole Alexandromys evoronensis (Kovalskaya et Sokolov, 1980) with its two chromosomal races, “Evoron” (2n = 38–41, NF = 54–59) and “Argi” (2n = 34, 36, 37, NF = 51–56) is the endemic vole found in the Russian Far East. For the “Argi” chromosomal race, individuals from two isolated populations in mountain regions were investigated here for the first time using GTG-, GTC-, NOR methods. In the area under study, 8 new karyotype variants have been registered. The karyotype with 2n = 34 has a rare tandem fusion of three autosomes: two biarmed (Mev6 and Mev7) and one acrocentric (Mev14) to form a large biarmed chromosome (Mev6/7/14), all of which reveal a heterozygous state.
For A. evoronensis, the variation in the number of chromosomes exceeded the known estimate of 2n = 34, 36 and amounted to 2n = 34, 36, 38–41. The combination of all the variations of chromosomes for the species made it possible to describe 20 variants of the A. evoronensis karyotype, with 11 chromosomes being involved in multiple structural rearrangements. In the “Evoron” chromosomal race 4 chromosomes (Mev1, Mev4, Mev17, and Mev18) and in the “Argi” chromosomal race 9 chromosomes (Mev6, Mev7, Mev14, Mev13, Mev11, Mev15, Mev17, Mev18, and Mev19) were observed. Tandem and Robertsonian rearrangements (Mev17/18 and Mev17.18) were revealed in both chromosomal races “Evoron” and “Argi”.
Chromosomal races, chromosomal rearrangements, polymorphism, Robertsonian translocation, tandem fusion
With evolutionary processes underway, structural chromosomal rearrangements (fusion) could be of great importance (
Voles of the genus Microtus (Schrank, 1798) sensu lato represent one of the groups in which speciation processes are accompanied by intense chromosomal rearrangements (
The Evoron vole A. evoronensis is the endemic vole species found in the intermountain landscape of the southern Russian Far East (Fig.
The map showing the collection localities of the Alexandromys evoronensis specimens was used in this study with the following legend: black circles stand for “Evoron” chromosomal race Nos. 1–5 according to
We have confirmed the chromosomal polymorphism of A. evoronensis (
Three variants of acrocentric chromosomes fusions and one variant of metacentric chromosomes fusion were first suggested using the G-banding of the chromosomes of voles from Lake Evoron shores without numbers for all pairs (
The variability in the number of chromosome arms may be related to the centromere positions in two pairs of autosomes (Mev8 and Mev13). All the detected chromosomal rearrangements of the Evoron vole karyotype of the “Evoron” chromosomal race were found in both homozygous and heterozygous states. The tandem fusion (Mev1/4) of two metacentric autosomes Mev1 and Mev4 was taken as a marker for the vole karyotype of the Evoron – Chukchagir lowland population (
This work focuses on studying structural rearrangements in two isolated populations of the “Argi” chromosomal race. A comparative analysis of chromosomal rearrangements in the “Argi” and “Evoron” chromosomal races using GTG-, GTC-, NOR methods was done, which revealed the similarity and difference of the two chromosomal races.
A total of 17 individuals of A. evoronensis (chromosomal race “Argi”) from two populations of the Russian Far East and 26 laboratory-bred voles were studied. Since the voles from five local populations (Nos. 1–5) of the “Evoron” chromosomal race have been studied before (
The voles studied were assigned a double number: zoological number/tissue sample number of mt DNA. The numbers were provided to link the present study with the previously published mt DNA data (
From population No. 7 in the Argi River valley of the Upper Zeya Plain in the Amur Region (54°40'10.62"N, 129°06'39.73"E), 9 individuals were caught in July 2015; females received the following identifying numbers: 3992 / 22–15 and 3997 / 27–15; male numbers were 3950 / 4–15, 3991 / 21–15, 3993 / 23–15, 3994 / 24–15, 3995 / 25–15, 3996 / 26–15, 3999 / 29–15. The karyotypes of 22 laboratory-bred individuals from parental individuals – female 3992 and males 3995, 3996 with 2n = 36 were also studied.
Chromosome suspensions were prepared from femoral bone marrow cells using the standard method (
Chromosomal characteristics of karyotype variants and the scheme of variable pairs of autosomes of Alexandromys evoronensis from two localities – the Verkhnebureinskaya Depression (No. 6) and the Verkhnezeiskaya Plain (No. 7).
Autosome number | Number and morphology of autosome pairs | Population | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
No. 6 | No. 7 | |||||||||
2n | NF | M | A+ St | 13/15 (v) or 13.15 (x) | 17/18 (v) or 17.18 (x) | 7 | 10 | 6/7/14 | Zoological number of animals | |
37a | 55 | 16 | 19 | x v | x x | x x | v v | 4554 m | ||
37b | 55 | 16 | 19 | x v | x v | x x | v v | 4556 f | ||
36a | 54 | 16 | 18 | v v | x x | x x | v v | Lb | 3992 f, 3950 m, 3991 m, Lb | |
36b | 56 | 18 | 16 | x x | x x | x x | v v | Lb, 4548 m, 4550 f, 4557 f, | Lb | |
36c | 55 | 17 | 17 | xv | xx | xx | vv | 4549 f | 3994 m, 3997 f, 3999 m, 3995 m, Lb | |
36d | 55 | 15 | 19 | v v | x v | x x | v v | 4567 f | 3996 m | |
34a | 51 | 15 | 17 | v v | x x | x | v | X | 4553 f | |
34b | 52 | 16 | 16 | x v | x x | x | v | X | 3993 m | |
Variations | 51–56 | 16–18 | 15–19 | 8 | 9 |
We used the karyotype of the race “Evoron” (GTG method) with the highest 2n (42) number, including 26 acrocentric (A) and 14 biarmed (M) autosomes (
For the tandem (TTel and TCen) and Robertsonian (Rb) fusions, two different markings of the chromosomes were used. The first marking corresponds to the tandem fusion, forming acrocentrics pairs (Mev11/19; Mev17/18 and Mev 13/15), while the second one corresponds to the Robertsonian fusion (Rb), forming metacentrics (Mev17.18 and 13.15). The different morphology possibly was the result of a centromere shift (or centromere reposition).
At least 20 chromosome plates per individual were performed to determine the number of chromosomes. The Axio Imager 1 microscope with the digital camera (AxioCamHR) and the software (Axiovision 4.7, Germany) as part of the equipment of the Joint Use Center “Biotechnology and Genetic Engineering” of the Federal Scientific Center for Terrestrial Biodiversity of East Asia, the Far East, Department of the Russian Academy of Sciences (Vladivostok, Russia) were used.
We studied two wild populations of voles (n = 17, see the Table
Variant 2n = 36a, NF = 54 (Fig.
Variant 2n = 36b, NF = 56 contains 18 biarmed and 16 acrocentric autosomes. The Mev13.15 and Mev17.18 were defined as metacentric. This variant was found in voles of population No. 6 and laboratory lineage of population No. 7 (Fig.
Karyotype of the Alexandromys evoronensis animals of the chromosomal race “Argi” with 2n = 36 a GTG-banded, 2n = 36c, # 4548, male from population No. 6 b C-banded, 2n = 36a, # 3950, male from population No. 7 c NORs, 2n = 36b, male of laboratory-bred from population No. 7. Black dots mark centromere positions in three pairs of chromosomes formed by the fusion of acrocentrics of the “Evoron” chromosomal race.
Variant 2n = 36c, NF = 55 (Fig.
Variants of the Alexandromys evoronensis karyotype of the chromosomal race “Argi”. The square shows variable chromosomes a 2n = 36a, male, laboratory-bred from population No. 7 b 2n = 36b, # 4557 female from population No. 6 c 2n = 36c, male laboratory-bred from population No. 7 d 2n = 36d, # 4567 female, the square shows variable pair Mev17/18, and 17.18 e 2n = 37a, # 4554 male, population No. 6 the square shows rearrangement in Mev4, and heterozygous Mev13.15, 13/15 f 2n = 34a, # 4553 female, population No. 6, the square shows tandem translocation pairs Mev 6, 7 and 14 in heterozygous state.
Variant 2n = 36d, NF = 55 (Fig.
Most of the voles (76.5%) of the two wild populations studied had the karyotype 2n = 36, which we defined as the main karyotype for the “Argi” chromosomal race (Table
The NORs localized in the pericentromeric regions of the Mev17/18 and Mev20 of the “Argi” chromosomal race (Fig.
We have also found morphological variability of the chromosomes in Mev9, Mev12, and Mev16 (Fig.
Variant 2n = 34a, NF = 51 consists of 15 metacentric and 17 acrocentric autosomes. Both homologs of the Mev13/15 were acrocentrics (Fig.
Variant 2n = 34b, NF = 52 includes 16 metacentric and 16 acrocentric autosomes, the chromosomes Mev13/15 and Mev13.15 were heteromorphic (Fig.
Karyotype of the Alexandromys evoronensis with tandem fusion of three autosomes: Mev6, Mev7, Mev14, and formation of a large biarmed element Mev6/7/14, 2n = 34b, # 3993 male. Black dots mark centromere in chromosomes involved in rearrangements.
A decrease in the chromosome number is associated with the tandem fusion of three autosomes: Mev6, Mev7, Mev14, and the formation of a large biarmed element Mev6/7/14. All four chromosomes are in a heterozygous state (Table
Each population (Nos. 6 and Nos. 7) of the “Argi” chromosomal race revealed one individual with 2n = 34 (Table
Variant 2n = 37a, NF = 55 (Fig.
Variant 2n = 37b, NF = 55 (see the Table
This study describes Evoron voles of the “Argi” chromosomal race, with their 8 variants of the karyotype and a minimal number of chromosomes (2n = 34) as well as acrocentrics (16), as being previously not found for A. evoronensis. All karyotypes of voles from the two populations studied (Nos. 6 and Nos. 7) showed an acrocentric Mev11/19 to be in a homozygous state, which indicates that chromosomes had already stabilized. Chromosomes Mev13/15 and Mev13.15 in the karyotypes of both populations had a different combination (A, A; A, M; M, M), which indicates the inability of this translocation to stabilize. We can assume the possibility of the centromere repositioning as well.
After sixteen months of breeding of animals from population No. 7 in our animal facility, we got 18 litters in the first and second generations with 92 young ones from natural parents with 2n = 36 and their descendants. Twenty-two karyotyped laboratory voles (F1) with 2n = 36 showed the frequency of individuals with variable chromosome morphology of Mev13/15 and Mev13.15 (A, A; A, M; M, M) to meet a 1: 2: 1 distribution. Animals with a different chromosome number were not bred. The distribution of variants of the Mev13/15 and Mev13.15 indicates that this rearrangement has no impact on the fertility and viability of the offspring. The morphological differences in the Mev13/15 and Mev13.15 chromosomes could be explained by assuming two scenarios of chromosome fusion. The first one should be a centromere-centromere, while the second scenario should support a fusion of the centromere and telomere with different centromere inactivation, and thus forming pairs of different morphologies, as was observed for the Mev17/18 and Mev17.18 chromosomes of the “Evoron” chromosomal race (
We demonstrated that two local populations (Nos. 6 and Nos. 7) of the “Argi” chromosomal race, separated by mountain ranges (Fig.
It is noteworthy that the 2n = 36 karyotype with these changed chromosomes exists in two geographically isolated populations, with the distance between these populations being about 500 kilometers. A recent time of divergence for Alexandromys was demonstrated using mt DNA data (
Scheme of the structural chromosomal rearrangements of the chromosome races “Argi” and “Evoron” identified in karyotypes with different numbers of chromosomes. Circles – centromeric, squares – telomeric fusion of chromosomes; asterisk – heterozygous state. The numbers on the edge of the diagram correspond to the diploid numbers found.
Analysis of numerous rearrangements in mitosis and meiosis of the Microtus species of the Russian fauna showed that in most cases, structural rearrangements that do not affect linkage groups of important genes do not result in disruption of meiosis, nor do they serve as an obstacle to their fixation in populations. In most cases, changes revealed in centromere position are brought about by repeated chromosome fusion, with random inactivation of centromeres belonging to different chromosomes (
The range of voles with an ancestral karyotype (2n = 42) could cover the area from Lake Baikal to the coast of the Sea of Okhotsk in the eastern part of Siberia. According to
For example, in the Middle Holocene, 7–5 thousand years ago, peculiar meadow steppes were widespread in the intermountain basins of Northern Transbaikalia (
According to
A. maximowiczii karyotype also underwent structural and intrachromosomal rearrangements (
Previously, for ten Palearctic vole species (whose chromosome number varied from 30 to 50), comparative G-banding and chromosome staining with specific Microtus agrestis (Linnaeus, 1961) revealed chromosomal rearrangements that distinguish this species from its ancestral karyotype (2n = 54) (
On average, one rearrangement of this type (fusion / fission) was believed to occur once every million years (
The chromosome painting data that are now available for many species from different orders (
Structural chromosomal rearrangements of “maximowiczii” voles in Asia (A. maximowiczii and A. evoronensis), as well as species of the genus Microtus in Europe, occurred in isolated mountain populations during the Late Pleistocene and Holocene climate change. Studies of karyotype transformation in various species allow us better to understand the role of chromosomal rearrangements in speciation.
Thus, we demonstrated two isolated populations of the “Argi” chromosomal race to have identical polymorphism (2n = 34, 36, 37, NF = 51–56). We revealed the multiple chromosomal rearrangements with the tandem fusions (Mev11/19, Mev13/15, Mev17/18, Mev6/7/14) and the Robertsonian translocations (Mev13.15 and Mev17.18) that led to eight new variants of the karyotype described. We observed the tandem fusion (Mev6/7/14) of chromosomes in heterozygous states in both populations.
For A. evoronensis, the variation in the number of chromosomes exceeded the known 2n = 34, 36 up to 2n = 34, 36, 38–41. The combination of all the variations of chromosomes for the species made it possible to describe 20 variants of the A. evoronensis karyotype, with 11 chromosomes which being involved in multiple structural rearrangements. In the “Evoron” chromosomal race 4 chromosomes (Mev1, Mev4, Mev17, and Mev18) and in the “Argi” chromosomal race 9 chromosomes (Mev6, Mev7, Mev14, Mev13, Mev11, Mev15, Mev17, Mev18, and Mev19) were observed. Tandem and Robertsonian rearrangements (Mev17/18 and Mev17.18) were revealed in both “Evoron” and “Argi” chromosomal races.
We thank Evgenia V. Terekhova, Prof., Chair, Foreign Lang. Dept., Far Eastern Branch, Russian Academy of Sciences for translating the paper. Our thanks also go to Natalia A. Lemskaya, Ph. D., Institute of Molecular and Cellular Biology SB RAS for help in differential standing chromosomes of voles from population No. 6. We also thank Marten Davenport and Lev Fedorov from Oregon Health Science University for proofreading our manuscript and helpful discussion. This study was partially supported by the Russian Foundation for Basic Research, Project No. 15-04-03871; the approved Research Theme is No. 0207-2021-0007.
Irina V. Kartavtseva https://orcid.org/0000-0003-2136-8253
Irina N. Sheremetyeva https://orcid.org/0000-0003-3464-9009
Marina V. Pavlenko https://orcid.org/0000-0002-7772-7019