She is pregnant all the time! Decoding the science behind Swamp wallabies unique reproductive plan

New Delhi, Mar 04: Swamp wallaby, a marsupial related to the kangaroo, are known for their very different reproductive strategies compared to other mammals. Typically, they conceive a new embryo days before delivering the newborn from its previous pregnancy.

A recent research boosted the decades-old hypothesis that female swamp wallabies (Wallabia bicolor) can start a second pregnancy before finishing their first. By alternating embryo implantations between two reproductive tracts, these marsupials can gestate nonstop throughout their entire adulthoods.

As described in a paper published March 2 in the Proceedings of the National Academy of Science, the animals typically conceive one to two days before giving birth.

How it works

Unlike humans, kangaroos and wallabies have two uteri. The new embryo formed at the end of pregnancy develops in the second, "unused" uterus. Then, once the newborn from the first pregnancy begins to suck milk, the new embryo enters a long period of developmental arrest that may last up to 11 months or more.

They have a very different reproductive strategy to most eutherian mammals whereby young are born at a highly altricial stage of development with the majority of development occurring over a lengthy lactation period. Furthermore, the timings of ovulation and birth in some species occurs within a very short interval of each other (sometimes hours).

Female swamp wallabies have an oestrous cycle shorter than their pregnancy length and were, therefore, speculated to mate and form a new embryo before birth thereby supporting two conceptuses at different stages of pregnancy.

"Thus, females are permanently pregnant their whole lives," says Brandon Menzies of the University of Melbourne, who collaborated on the research with Marilyn Renfree and Thomas Hildebrandt, professors at the Leibniz Institute for Zoo and Wildlife research in Berlin, Germany.