Ecology


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Sexual Reproduction and Development

Introduction.

Male Reproductive System.

Female Reproductive System.

Seasonal Breeding.

Pregnancy, Birth and Diapause
Pregnancy - Pregnancy in marsupials is very short lived (relative to placentals), lasting from as short as 12.5 days (in Northern Brown and Long Nosed Bandicoots).

Birth - After the gestation period, a foetus will indicate it is ready for birth by producing the hormone cortisol, which causes the release of prostaglandin hormones that initiate uterine contractions. At this point, the female will usually crouch or curl up to bring the urinogenital opening though which the young will pass closer to the pouch/mammary area. Mesotocin, the marsupial hormone equivalent of oxytocin, is then produced by the mother in a positive feedback loop to continue the uterine contractions until the live young is delivered. Birth occurs through the larger median vagina, which acts as the birth canal.

The infant is tiny and poorly developed, referred to as an 'embryonic' condition birth. Immediately following birth, the newborn must move unaided by crawling using its' slightly more developed forearms up to the pouch or mammary glands of its' mother and attach to a teat to suckle. How the newborn navigates its' way up to the teats is unknown, but it has been theorised that possible aids are gravity and/or smell.
baby (55K)
Pygmy possum newborn in human palm, clearly demonstrating
typical marsupial small size at birth but with relatively well developed forearms


Diapause - In some groups of marsupials, gestation and the luteal phase are extended to overlap with the next follicular development period, so if mating occurs soon after birth (sometimes as soon as a matter of hours in macropodids), it possible to fertilise a new egg. However, suckling of the newborn produces a hormone called prolactin which prevents the development of the corpus luteum. Without progesterone secreted by the corpus luteum, the embryo cannot develop past a 100-cell blastocyst stage. This pause in development is called 'diapause'. When the newborn has been weaned, prolactin is no longer produced and embryonic development can continue.

Lactation.