Context: The Swamp Wallaby is likely the only mammal pregnant and lactating all life long, said the researchers, from the University of Melbourne and the Leibniz Institute for Zoo and Wildlife Research, Berlin. Their study is published in the journal PNAS (Proceedings of the National Academy of Sciences of the USA).

About:

• It typically conceives a new embryo days before delivering the newborn from its previous pregnancy.
• Female wallabies have two uteri and two separate ovaries. At the end of a pregnancy in one uterus, a new embryo develops in the other uterus. 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 the swamp wallaby (Wallabia bicolor), the new conception happens one or two days before the previous joey is delivered.

Why this study matter?

• Apart from the general finding, it can tell us much about the broader evolution of reproductive trends in mammals.
• Most mammals have long pregnancies that surpass the length of the oestrous cycle — the fertile period when they mate and conceive. “Here we can see there is a marsupial that has continued pregnancy through the oestrous cycle for the first time, which tells us definitely that marsupials are not constrained by this time relative to all other mammals. 
• It is not the general pattern in mammals to conceive during active pregnancy for many reason.
• So by studying the swamp wallaby or animals that do things differently or uniquely, we can discover novel molecules or mechanisms that might have applications for human pregnancy or disease.”