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Focus: GS-III Environment and Ecology

Why in news?  

The swamp wallaby is likely the only mammal pregnant and lactating all life long, researchers have said.

How is it possible? 

  • 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.
  • 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 birth.
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What happens after birth?

  • 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.

The hare parallel: 

  • There is only one other mammal, the European brown hare (Lepus europaeus), that conceives additional embryos before giving birth.
  • There are, however, two key differences. In the hare, the new embryos are conceived in the same uterus that is already supporting foetuses in late stages — which, the researchers note, may be all the more remarkable.
  • The other difference is that only the swamp wallaby is pregnant all its life.
  • “The hare is only pregnant with the possibility of conceiving new embryos during distinct breeding seasons over about 5-6 months of the year. The rest of the time it is not pregnant or lactating at all.

About Swamp Wallaby:

  • The swamp wallaby is a small macropod marsupial of eastern Australia.
  • It inhabits thick undergrowth in forests and woodlands, or shelter during the day in thick grass or ferns, emerging at night to feed.

March 2024