Ea. Gileva et al., CHROMOSOMAL SPECIATION AND FOLLICULOGENESIS IN THE SEMISTERILE INTERSPECIFIC HYBRIDS OF THE VARYING LEMMINGS, GENUS DICROSTONYX, Zurnal obsej biologii, 55(6), 1994, pp. 700-707
Karyotypes of Dicrostonyx torquatus torquatus and D. vinogradovi that
are very similar phenotypically differ at least by 13-14 chromosomal r
earrangements including centric and tandem fusions, fissions and parac
entric inversion. In their male hybrid F1 spermatogenesis is arrested
on early pre-meiotic stages, the female hybrids are semisterile. Histo
logical investigation of ovaries has demonstrated reduced number of fo
llicles, higher percentage of atretic follicles and an acceleration of
folliculogenesis in hybrids as compared with the parental forms. As a
result of the acceleration, the number of mature follicles and ovulat
ions is not significantly diminished in the hybrid females, and their
semisterility is caused, to a great extent, by high prenatal loss whic
h most likely arises from the chromosomal imbalance in F2 hybrids. Thu
s, the mechanism suggested by the concept of chromosomal speciation is
active, but not alone in forming reproductive isolation between twin
species of the varying lemming.