The B chromosome system in the varying lemming Dicrostonyx torquatus Pall., 1779 from natural and laboratory populations

In varying lemmings from seven natural populations (from Bol’shezemel’skaya tundra to Chukotka Peninsula), the number of B chromosomes ranged from 0 to 15. In populations surveyed for several years, B chromosome frequencies were stable. Two laboratory colonies (founded by Dicrostonyx torquatus torquatus from the Polar Urals and D. t. chionopaes from Yakutia) produced more than 3000 animals, of which 1699 were karyotyped. A small excess of B chromosomes in the progeny over that in their parents was observed in each generation. Coefficients of transmission k1 of additional chromosomes were on average 0.519 in D. t. torquatus and 0.511 in D. t. chionopaes. In oocytes I and II, an accumulation of B chromosomes was observed as compared to somatic cells ( k2 = 0.66). The reproductive output of animals from both laboratory colonies did not depend on size of the B genome. The reduction of body and scull sizes observed in animals carrying numerous B chromosomes may confer negative selective value in the conditions of the Extreme North. In general, the system of B chromosomes in D. Torquatus is well balanced and very stable, being apparently under strong genetic control.