Is the highveld mole-rat Cryptomys hottentotus pretoriae (Rodentia: Bathyergidae) an induced or spontaneous ovulator?

Abstract

The highveld mole-rat Cryptomys hottentotus pretoriae is a social subterranean rodent that exhibits seasonal reproduction. Non-reproductive females remain anovulatory whilst in the confines of the natal colony. However, during the southern hemisphere summer, dispersal of non-reproductive females from the natal colony occurs with subsequent pairing with unrelated males. This study investigates whether the dispersing female highveld mole-rat is an induced or spontaneous ovulator. Eight non-reproductive females were removed from their natal colonies during the breeding season and housed individually for 5 weeks. Urine was collected every second day during the next 5 weeks of isolation. After this initial period, isolated females underwent one of three trials: two females were kept isolated without a male, three females were individually placed in chemical but not physical contact with unvasectomized males, while each of the remaining three females were allowed full contact with a vasectomized male. Urine was again collected every second day for a further 5 weeks, after which the females were killed. Both urinary progesterone profiles and histology of the ovaries revealed that the female highveld mole-rat is an induced ovulator. Females in physical contact with vasectomized males exhibited a significant increase in urinary progesterone concentration as well as the presence of corpora lutea in their ovaries, both indicative of ovulation. The act of coitus is necessary for ovulation to take place even though the males were not capable of fertilization. This is the first time induced ovulation has been shown in bathyergid rodents.