Changes in the Ovaries and Uterus of the Dugong, Dugong dugon (Sirenia:Dugongidae), with Age and Reproductive Activity

Abstract

The uterus and ovaries from 49 dugongs of a variety of ages and levels of reproductive activity have been studied macroscopically and histologically. The ovaries are large, flattened, ovoid organs in which the germinal epithelial surface is almost two-dimensional. Numerous Graafian follicles develop in the ovaries of a female approaching oestrus; at least several of these follicles rupture; some corpora lutea may result from luteinized follicles; a second generation of corpora lutea may form in the presence of the first. Thus the dugong seems to be polyovular and polyoestrus. The large number (up to 30+) of corpora lutea persist throughout pregnancy and subsequently regress to brown corpora albicantia which seem to persist for at least several years. Ovarian pathology and parasites are documented. The cycle of endometrial changes in the bicornuate uterus is described. Conspicuous scars (deposits of haemosiderin) mark the sites of previous (zonary) placental attachments and probably persist for life. The high proportion of mature females sampled that were neither pregnant nor lactating, and the observed high frequency of sterile cycles, suggest that fecundity is low in north Queensland populations of dugongs.