Swamp wallaby never stops being pregnant
Female swamp wallabies are constantly pregnant during adulthood.
March 4 (UPI) -- The female swamp wallaby, native to eastern Australia, is the only mammal that remains pregnant for the entirety of adulthood, according to a new study.
Like kangaroos, wallabies have two uteri. During the later stages of a swamp wallaby's most immediate pregnancy, a new embryo forms in the unused uterus. When the wallaby gives birth and the newborn joey starts suckling milk, the new embryo enters a long period of developmental arrest called embryonic diapause.
When the young wallaby's appetite for milk starts to wane, the embryo begins growing once more and the pregnancy cycle starts anew. The female wallaby becomes fertile and she seeks out a new mate to form a second embryo.
"Thus, females are permanently pregnant their whole lives," lead researcher Brandon Menzies, geneticist and marsupial expert at the University of Melbourne, said in a news release.
Most mammals need a break in between pregnancies to help raise newborns or avoid seasonal dips in food resources, but the latest research -- published this week in the journal PNAS -- suggests the female swamp wallaby never takes a day off from being pregnant.
"We used high resolution ultrasound to track pregnancy and mating in 10 female swamp wallabies," said Menzies. "What we found amazed us: the females come into oestrus, mate and form a new embryo 1 to 2 days before the end of their existing pregnancy. The swamp wallaby is the only mammal known to be continuously pregnant in this way."
Because the swamp wallaby is always pregnant, moms are always supporting three different stages of development: an embryo in the uterus, a young joey in the pouch and a semi-dependent young still suckling milk. Despite these heavy demands on female swamp wallabies, surveys suggest the species is doing well.
"Whatever the reason, the swamp wallaby is an incredibly successful and ubiquitous species in Australia, occupying a range that stretches from the Western Victoria/South Australian border all the way up the eastern seaboard to cape York in far north Queensland," said Menzies.
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