Variability in Size of the Nuclear Genome in Pygmy Wood Mouse Sylvaemus uralensis (Rodentia, Muridae)

Abstract

Earlier, in an integral genetic study, the Asian and European races were distinguished within the species Sylvaemus uralensis (pygmy wood mouse) and the European race was divided into the East European and South European forms. Each of these groups differed from the others, in particular, in the quantity of the centromeric heterochromatin in karyotypes of the animals. To establish the pattern of its changes in S. uralensis, in the present study the DNA content in splenocyte nuclei in all races and forms of pygmy wood mice was assessed using DNA flow cytometry. The heterochromatin amount in karyotypes and genome size were shown to be correlated. The East European chromosomal race of S. uralensis (Central Chernozem and Non-Chernozem regions of Russia, Crimea Peninsula, Middle Volga region, and Southern Ural) and the Asian race of this species (East Kazakhstan, Uzbekistan, and East Turkmenistan), which have respectively the highest and the lowest amounts of centromeric heterochromatin in the karyotype, exhibit the greatest difference in the DNA content in the genome. On average, the difference is approximately 8% in males and 6.7% in females; in both cases, the ranges of variability were distinctly different. Against the general background of the trait variation, the Asian race, whose members have the smallest DNA amount in their cells, looks homogeneous. The genome of the South European chromosomal form of S. uralensis (Caucasus, Transcaucasia, Carpathians, and Balkan Peninsula), which exhibits an intermediate content of the centromeric heterochromatin in the karyotype, is smaller that the genome of the East European race (by 3.2% in the group of males and by 1.9%, in the group of females), but larger than that of the Asian race (by 5% in either sex). Thus, the variability of size of centromeric C-blocks in pygmy wood mouse is likely to be associated with elimination (or, conversely, an increase in the amount) of the genetically inert chromatin. It is suggested that a significant contribution to the variability of genome size in S. uralensis is made by heterochromosomes, or, more precisely, their variable regions, which seem to be largely heterochromatic. ANIMAL GENETICS

Genetic variation and differentiation of wood mice from the genus Sylvaemus inferred from sequencing of the cytochrome oxidase subunit 1 gene fragment

“…Chromosomal Form Russia, Krasnodar krai, the city of Sochi tributary area: (17) outskirts of the city of Khosta (one speci men); (18) outskirts of the settlement of Krasnaya Polyana (four specimens); (19) Russia, Kabardino Balkar Republic, outskirts of the city of Nalchik (three specimens); (20) Armenia, Lori region, outskirts of the settlement of Lermontovo (two specimens); (21) Azerbaijan, Leriksky district, Talysh, outskirts of the settlement of Orand (two specimens).…”

“…Some of these species (wide range wood mouse S. syl vaticus and pygmy wood mouse S. uralensis) are, in turn, characterized by complex genetic variation and differentiation [3][4][5][6][7][9][10][11][12][13][14][15][16][17][18][19]. Specifically, in S. uralen sis, Asian and European races are described.…”

“…More over, within the latter race, eastern European and southern European chromosomal forms are distin guished. These forms are close to each other and only slightly different in the number of large centromeric heterochromatin blocks and the genome size [9,10,[12][13][14][15][16][17]19]. Based on analysis of individual genetic markers, some authors suggested that the European and Asian races, as well as the southern European chromosomal form, should be treated as independent species (under the names of S. uralensis s.…”