Reproduction in Monotremes and Marsupials


The three subclasses of mammals are most clearly distinguished from one another by their mode of reproduction and the anatomy of their reproductive tracts. The three species of monotreme are all oviparous, whereas the 276 or more living species of marsupial all give birth to small, altricial young that in most species are retained in the mother's pouch during the extended lactational period.

Keywords: pouch; altricial young; platypus; kangaroo; lactation

Figure 1.

Hormonal profiles during pregnancy and the oestrous cycle in (a) the tammar wallabyMacropus eugenii and (b) the quoll Dasyurus viverrinus. In tammars, as in most macropodids, pregnancy and the associated increase in progesterone levels (red line) lasts almost as long as the oestrous cycle. At the end of pregnancy a follicle matures on the ovary with an associated rise of oestradiol (blue line). Oestrus occurs within a few hours after birth, and the resulting embryo will enter and remain in diapause whilst the newborn young remains in the pouch. There is a surge of progesterone 5–7 days after suckling ends which coincides with reactivation of the embryo. In quolls, and most other marsupials, pregnancy is much shorter than the oestrous cycle. The presence of young sucking in the pouch inhibits further follicle development and oestrous is inhibited.

Figure 2.

Reproductive patterns in (a) the red kangaroo and (b) the tammar. Red kangaroos have a continuous breeding strategy. Females come into oestrous (E) immediately after birth (B). The embryo enters diapause (d) while the young is in the pouch. In late lactation the embryo reactivates and is born about 1 month later whilst the larger young is out of the pouch but still suckling, with another postpartum oestrous. In severe drought lactation may fail and the young is lost allowing reactivation of the diapausing embryo. If drought continues females will enter anoestrus (A), and will resume cycles only when the drought breaks. Tammars are seasonal breeders. Females give birth in late January with a postpartum oestrus. Diapause continues under lactational control until about May, when seasonal photoperiodic influences take over the inhibition. Soon after the summer solstice, the falling day length allows reactivation, with birth and new postpartum oestrus in mid to late January. Inset: tammar blastocyst in diapause. The unilaminar blastocyst is surrounded by a mucoid coat and shell membrane.

Figure 3.

Representative monotreme (echidna; a,c) and marsupial (tammar wallaby; b,d) reproductive systems. In females (a,b) the ureters pass medially preventing fusion to form a single uterus as occurs in most eutherian mammals. In male monotremes (c) the testes are held within the abdominal cavity, whilst in most male marsupials (d) the testes descend into a scrotum (not shown) anterior to the penis. The echidna is illustrated with the penis sheathed in its preputial sac, its normal position; in (d) the tammar penis is shown extended from the urogenital opening. There is a single urogenital opening in both males and females.


Further Reading

Augee ML (ed.) (1992) Platypus and Echidnas. Mosman, NSW: Royal Zoological Society of New South Wales.

Griffiths ME (1978) The Biology of Monotremes. New York: Academic Press.

Griffiths ME (1984) Mammals: monotremes. In: Lamming GE (ed.) Marshall's Physiology of Reproduction, 4th edn, vol. 1: Reproductive Cycles of Vertebrates, pp. 351–385. Edinburgh, UK: Churchill Livingstone.

Renfree MB (1993) Ontogeny, genetic control and phylogeny of female reproduction in monotreme and therian mammals. In: Szalay FS, Novacek JJ and McKenna MC (eds) Mammal Phylogeny, pp. 4–20. New York: Springer.

Renfree MB (1994) Endocrinology of pregnancy, parturition and lactation of marsupials. In: Lamming GE (ed.) Marshall's Physiology of Reproduction, 4th edn, vol. 3: Pregnancy and Lactation, pp. 677–766. London: Chapman and Hall.

Renfree MB and Shaw G (1998) Marsupials. In: Knobil E (ed.) Encyclopedia of Reproduction, vol. 2. San Diego, CA: Academic Press.

Saunders NA and Hinds LA (eds) (1997) Recent Advances in Marsupial Biology. Kensington, NSW: University of New South Wales Press.

Tyndale‐Biscoe CH (1984) Mammals: marsupials. In: Lamming GE (ed.) Marshall's Physiology of Reproduction, 4th edn, vol. 1: Reproductive Cycles of Vertebrates, pp. 386–454. Edinburgh, UK: Churchill Livingstone.

Tyndale‐Biscoe CH and Renfree MB (1987) Reproductive Physiology of Marsupials. Cambridge: Cambridge University Press.

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Renfree, Marilyn, and Shaw, Geoffrey(May 2001) Reproduction in Monotremes and Marsupials. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001856]