Role of the Corpus Luteum in Marsupial Reproduction

Abstract

IN marsupials the histological changes which occur in the ovaries and uteri of unmated females after ovulation appear to be very similar both in degree and duration to those occurring during pregnancy1. The gestation period is shorter than the length of an œstrous cycle in all the polyœstrous marsupial species so far investigated, and some workers consider that this can be accounted for by a similarity between the duration of the functional life of the corpus luteum in pregnant and non-pregnant females, and of the gestation period2. Thus, Sharman3 and Amoroso4 postulate that the hormonal control both of the œstrous cycle and of pregnancy may be identical and that the simple yolk-sac placenta characteristic of most marsupials probably has little or no endocrine function comparable to that of the true allantoic placenta of eutherian mammals. One of the implications of this hypothesis is that pregnancy in marsupials would be largely maintained by the progesterone produced by the corpus luteum. However, a few marsupials, including the long-nosed bandicoot Perameles nasuta Geoffroy, have true allantoic placentae5,6 and therefore the reproductive physiology of such species is of considerable interest.