Kartavtseva I.V., Stepanova A.I.
Zoologicheskiy zhurnal 2024; 103(12): 91-107
Previously, only Alexandromys fortis has been found to occur in the northeastern part of the Middle Amur Lowland. Karyotype studies on voles at the northernmost locality of the lowland, near the village of Elban, reveal a second species, A. maximowiczii, shifting its eastern range limit 200 km east of the nearest known one. Four karyotype variants found in individuals from the Middle Amur Lowland are described for the first time for Maximowicz’s vole which shows multiple chromosomal polymorphism. Two karyotype variants are found to predominate: 2n = 40, NF = 58 and 2n = 41a, NF = 60, vs firther two which are rare:2n = 41b, NF = 59 and 2n = 41c, NF = 59. According to the 2n and NF numbers, these variants correspond to the chromosomal form “C”. The variability of the chromosome number in this species is due to the tandem fusion of metacentric chromosomes № 3 and № 4 to form a large metacentric № 3/4. Centric fusion of acrocentric chromosomes № 11 and № 20 to form a medium-sized metacentric chromosome № 11.20 is generally stabilized, with the exception of one individual of 54 examined. A sharp decrease in heterozygotes for tandem fusion is noted for individuals in the middle part of the lowland, vs the northeastern part where it was high. The number of chromosomes being 39 is excluded from the chromosomal form “C” as unsubstantiated. Rare variants have one pair of autosomes in the heterozygous state (SM/A). Such a variability seem to be associated with a shift in the centromere in chromosome № 10 in variant 41b and a pericentric inversion in chromosome № 16 in variant 41c. Based on the previously published data of genetic analyses, allozyme, chromosomal and molecular-genetic for both species involved, A. maximowiczii and A. fortis, chromosomal characteristics and their habitats, including syntopic ones, are presented.
