Adoptions and Offspring Swapping Stun Kangaroo Researchers Your Diet Guide

Adoptions and Offspring Swapping Stun Kangaroo Researchers

Posted by Taylah Degotardi 30 Jun, 2011

(ISNS)—Kangaroos adopt. It doesn’t happen often, but to the astonishment of biologists at Wilsons Promontory National Park in Australia, sometimes a mother bends forward, opens her arms and invites someone else’s youngster to hop into her pouch.

Once made, the mix-up endures, lasting through the remaining weeks of “pouch life” and on during months of the “young-at-foot” stage, when the growing juvenile kangaroo continues to nurse.

“It’s a complete surprise to us,” said Graeme Coulson, a zoology professor at the University of Melbourne in Australia.

Coulson described the baby swapping in which two mothers end up with each other’s young this month at a joint meeting of the American Society of Mammalogists and the Australian Mammal Society in Portland, Ore.

Although rare cases of marsupial fostering have previously been reported in captivity, and biologists have used fostering in breeding programs, this appears to be the first documented report of spontaneous adoptions in the wild, said Roberta Bencini, vice president of the Australian Mammal Society and professor of animal biology at the University of Western Australia.

“That’s really quite an unusual discovery,” said Bencini, who was not involved in Coulson’s research. “I would like to find out why.”

So would Coulson.

The exchanges seem to have no apparent benefit for the mother, who squanders her own resources on another’s offspring, Coulson said. His best guess is that the swaps are simply an error by one mother later compounded or perhaps just accepted by another.

According to doctoral student Wendy J. King from the University of Queensland in Australia, it might happen when a group of mothers is startled, perhaps by a predator attack. King said via email that nursing mothers are primed to accept a youngster into their pouch during the “in-and-out” phase, roughly two months when the young sometimes hop out to explore but then return. Although the mothers normally would push away the wrong one, King said that their recognition system might be overwhelmed by intense pressure from a predator.

Whatever causes them, Coulson said that these adoptions should help remind kangaroo researchers never to assume anything not even that the young in a mother’s pouch is her own genetic offspring.

Researchers discovered the adoptions partly because their work in Wilsons Promontory is so extensive. Hundreds of animals have been collared, given ear tags and genotyped from a tissue sample taken when they are tagged. The project, which began in 2008, is a 15-year-long study of population dynamics and reproductive strategies in the Eastern gray kangaroo.

Biologists first noticed something odd in October 2009. One of the tagged youngsters was no longer with its mother. At first, Coulson said, they wondered if they had made a mistake in record keeping. Then another mismatch turned up.

King said that so far the group has documented seven adoptions among 134 juvenile kangaroos it has marked, a 5 percent adoption rate. Four were simple swaps, with two mothers ending up with each other’s young. Because many kangaroos that use the park aren’t tagged, researchers don’t know who the mothers are for the other three they just know the genotypes don’t match. Interestingly, although some animals do help raise close relatives, biologists have ruled out strong kinship ties among the adoptive mothers. These aren’t sisters or other close relatives helping each other out.

Researchers are observing the kangaroos on a grassy swath of parkland that doubles as a landing strip for firefighting planes. It’s a favorite gathering area, partly because of the thick cover of nearby shrubs, and has attracted around 1,000 kangaroos.

That density might be one of the factors contributing to the adoptions, said Tony Friend, president of the Australian Mammal Society, who was not involved in the research. Because the adoption findings are so new, no one has yet had time to test that theory.

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