REPRODUCTIVE SUPPRESSION IN EUSOCIAL CRYPTOMYS DAMARENSIS COLONIES - SOCIALLY-INDUCED INFERTILITY IN FEMALES

Inhibition of reproduction occurs in colonies of the Damaraland mole-r at (Cryptomys damnrensis), where one female and usually one male are r eproductively active. They remain the sole reproductive animals throug hout their stay in the colony, which in the field may exceed five year s. An 18-month study on a captive colony of C. damarensis shows that n on-reproductive females remain anovulatory and always have concentrati ons of urinary progesterone lower than that of the reproductive female 10.7 +/- 8.8 nmols/mmol creatinine (n = 85), although their progester one concentrations are slightly elevated when the reproductive female is early in pregnancy. In contrast the reproductively active female ha s elevated concentrations of progesterone 63.3,70.1 nmols/mmol creatin ine (n = 14). Standard histological together with immunohistochemical examination of the ovarian structure shows that follicular development in the non-reproductive females is halted at varying stages prior to ovulation and that the unruptured follicles luteinize. These unrupture d luteinized follicles stain positive for 3 beta hydroxysteroid dehydr ogenase-the enzyme catalysing the synthesis of progesterone from pregn enolone. It is possible that the low levels of circulating progesteron e produced by the luteinized follicles in the non-reproductive females in the colony are sufficient to feedback on the hypothalamo-pituitary axis and prevent the surge of LH necessary for ovulation. Behavioural studies provide corroborative evidence for sexual suppression. Thus t he nonreproductive females in the colony are never involved in courtsh ip or copulatory behaviour, nor do they actively solicit males in the colony. The reproductive female, however, plays an active role in mate selection and is the initiator in courtship behaviour. The suppressio n of ovulation in non-reproductive females is maintained for as long a s there is a reproductive female in the colony.