Researchers reported that the swamp wallaby, a marsupial related to the kangaroo, is pregnant throughout its adult life. It typically conceives a new embryo days before delivering the newborn from its previous pregnancy.

Swamp wallaby

IUCN Status: Least Concerned

• The swamp wallaby is a small macropod marsupial of eastern Australia. It is likely the only mammal pregnant and lactating all lifelong.
• Female wallabies and kangaroos have two uteri and two separate ovaries.
• At the end of a pregnancy in one uterus, a new embryo develops in the other uterus.
• Kangaroos and wallabies regularly have an embryo in the uterus, a young joey in the pouch, and a third semi-dependent young at foot, still drinking its mother’s milk.

How it is different from Kangaroo?

• In kangaroos, the new embryo is conceived a day or two after the previous birth.
• In the swamp wallaby (Wallabia bicolor), the new conception happens one or two days before the previous joey is delivered.

What happens after?

• As soon as the mature foetus is born and settles in the pouch, the swamp wallaby arrests the development of the new embryo.
• This is called embryonic diapause, which happens in many animals to pause reproduction until the conditions are right — season, climate, food availability.
• For wallabies, this is also to ensure that the new one is born only when the pouch is free again.
• If this did not happen, the swamp wallaby would be birthing new young every 30 days — it has a short gestation period — and its pouch could not support that.

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