Reproduction and post-natal development in the marsupial Bettongia lesueur (Quoy & Gaimard)

Abstract

The female reproductive tract is described and compared with that of other Macropodidae. It is shown that the characters considered to be diagnostic of the Potoroinae are more variable than hitherto supposed and occur also in the Macropodinae. For the greater part of the oestrous cycle the lateral vaginae are probably occluded and the pseudovaginal canal closes within a day of parturition, so that the contents of the vaginal smear are derived mainly from the posterior vaginal sinus. B. lesueur is polyoestrous and monovular. The oestrous cycle has a modal length of 23 days and gestation modal length of 21 days, post-partum oestrus following about 1 day later. The reproductive cycle is delayed during lactation and embryonic diapause occurs. The young leaves the pouch at 115 days and the delayed embryo is born a few days later. Experimental removal of the pouch young results in resumption of development and birth 20 days after removal. The young weighs 0.317 g at birth and it reaches an adult weight at about 280 days, when sexual maturity is attained. Animals less than 1 yr old can be distinguished by the presence of the sectorial premolar 3 in the upper jaw, which is shed at 1 yr. The full adult dentition is attained by 18 months. In close confinement females bred regularly from February to September but about 70% spontaneously lost their young by the age of 3 weeks. In large pens young were carried through lactation to independence. Reproduction in Bettongia is compared to that of Potorous, a closely related rat-kangaroo, and a general hypothesis is developed to reconcile several disparate observations of marsupial reproduction. It is postulated that most marsupials have a period of obligatory diapause interposed in the development of the embryo, and this is followed by a short and relatively constant period of embryogenesis. The diapause may be short, as in Perameles, or long as in Potorous, and, in the special conditions of the Macropodidae may be greatly extended during lactation. This latter phenomenon may be secondarily advantageous to the species ecologically but it is emphasized that its primary adaptive significance is likely to be found in the need to synchronize embryonic and uterine development for intra-uterine nourishment of the embryo.