Maintaining 3 Joeys – Marsupial Lactation and Embryonic Diapause

Tammar Wallaby (Macropus eugenii)

Image via Wikipedia - Tammar Wallaby (Macropus eugenii)

An interesting fact that gets glossed over, is the number of young a mother marsupial can maintain at once. In the case of a kangaroo or the Tammar Wallaby, mothers can have up to 3 young in 3 completely different stages. This is due in part to their lactation (producing milk) being so variable. Embryonic diapause (the name for this reproductive strategy wherein development is delayed at the blastocycst stage) is one of my favorites, and I even wrote a paired paper on it  which included the hormonal aspects of delaying embryonic development for my college Mammalogy course. There are two types of embryonic diapause, obligate and facultative. “Obligate or seasonal diapause is more frequent in mammals with a single litter per year while facultative diapause is more frequent in mammals with multiple litters per year” (#2).

via - Newborn Wallaby attached to nipple (provided by K Nicholas, University of Melbourne)

There are three phases of lactation in marsupials. “Phase 1 is actually comparable to mammary development during gestation in eutherian mammals. Phase 2 is the early period of milk secretion when the joey is still in the pouch. Phase 3 coincides with the joey beginning to leave the pouch” (#1). Milk secretion usually occurs about 24 hours after birth of the joey. While a newborn may suckle one of the four teats, an older joey out of the pouch may be using another of the four teats. The unused nipples regress due to lack of stimulation and the two being suckled develop independently. Early lactation (phase 1- 2) milk composition is about 50% carbohydrate and low in lipids, followed by low carbs and up 60% or more lipid in phase 2-3. Protein levels are relatively constant throughout lactation.

“Shortly after the first joey is born, the mother mates again. This new embryo stays at an early dormant stage of development until the first joey begins to leave the pouch. The decline in suckling stimulus associated with the first joey leaving the pouch allows the second joey embryo to develop, be born and enter the pouch” (#1). This then frees the uterus and allows the mother to mate again and develop a third joey. In the event of disaster, Kangaroos can quickly repopulate during a poor season thanks to being so consistently pregnant. While the Tammar Wallaby is the most studied individual, other species that practice embryonic diapause include rodents, badgers, bats and minks. About 100 species use this reproductive strategy.




  1. : Lactation – Marsupials
  2. My group project on embryonic diapause


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