OVARIAN GROWTH AND FOLLICULOGENESIS IN BREEDING AND NONBREEDING FEMALES OF A SOCIAL RODENT, THE ZAMBIAN COMMON MOLE-RAT, CRYPTOMYS SP

Zambian common mole-rats are subterranean rodents that live in familie s with only one female breeding. Her offspring remain in the parental nest and do not reproduce. Behavioral experiments (Burda, '95) demonst rated that their apparent ''sterility'' is based on incest avoidance a nd individual recognition of family members. To elucidate whether some bind of morphologically apparent ovarian suppression still takes plac e in daughters, ovaries of females of known age, weight, and reproduct ive histories were examined histologically and morphometrically. The b ody mass of old females (more than 3 years of age) begins to decrease, and the ovaries seem to begin to atrophy at the age of about 3-6 year s. Ovaries in neonates exhibited primordial and primary follicles, som etimes clustered in nests. Ovaries of adult nonbreeding females expres sed all stages of the follicular development up to tertiary follicles. Many unruptured luteinized follicles were present, but true corpora l utea as a morphological sign of ovulation were missing. Unruptured lut einized follicles also could be found (additionally to true corpora lu tea) in ovaries of breeding females. The number of primordial follicle s dropped rapidly during the first 2 years of age; the number of prima ry, secondary, and tertiary follicles was subject to individual variat ion; and there was no clear correlation with age or reproductive statu s. While a tendency to form accessory unruptured luteinized follicles may just reflect taxonomic affinities of bathyergids to hystricomorphs , the otherwise complete folliculogenesis in ''sterile'' daughters and the presence of unruptured luteinized follicles even in breeding fema les are further evidence that there is no hormonal suppression of the ovarial cycle. We suggest that ovulation in nonbreeding females is not actively suppressed by the breeding female, but instead that it is no t released because the triggering mechanisms, most probably repeated c opulation, are missing. (C) 1998 Wiley-Liss, Inc.