Karyotypes and divergence of stream Dolly Varden from the southern Sakhalin

The karyotype of stream Dolly Varden inhabiting a tributary of the Belaya R iver (the basin of Naiba River, southern Sakhalin) was determined (2n = 82 and NF = 98 + 2). According to the main characteristics (chromosome number and arm number, the presence of a pair of marker submeta-subtelocentric chr omosomes with nucleolus organizer regions (NORs), one pair of large acrocen tric chromosomes, and one pair of subtelocentric chromosomes), this karyoty pe is identical to the karyotype of anadromous southern Dolly Varden form S alvelinus malma krasheninnikovi of Primorye and Japan. However, in most str eam Dolly Varden individuals, additional active nucleolus organizer regions (NORs) located in telomeric and paracentric regions of two to three pairs of acrocentric chromosomes were revealed. It is suggested that the stream a nd anadromous southern forms of Dolly Varden are evolutionarily related NOR s that are silent in the anadromous southern form and are active in the str eam form. Possible causes of these differences in NOR activity are discusse d.