The Monito del Monte, or "little mountain monkey" is a South American marsupial whose DNA links it to Australia's earliest known marsupial.
Credit: Wikimedia
SYDNEY: All living Australian marsupials share a long-lost ancestor from South America, according to new research using genomic markers to reconstruct their family tree.
The genomes of 20 Australian and South American marsupials including the Australian tammar wallaby and the South American opossum, were screened by a team lead by Maria Nilsson from the University of Muenster in Germany for repetitive DNA fragments known as retroposons.
The presence of shared retroposons in different species can be used to trace relationships and common ancestors. “Our study was the first to apply this method to marsupials, Nilsson said.
“And we could resolve parts of the marsupial family tree that have been debated for decades.”
Tracing marsupials back to South America
Mainly used by researchers to determine relationships between placental mammals – especially primates – retroposons, or ‘jumping genes’, are pieces of non-functional DNA that are copied from one ancestor to all its descendants.
As they are unlikely to arise independently in different species in exactly the same part of the genome by chance, shared retroposons can be used to determine relationships and ancestral lineage.
“Marsupial genomes consist of 52% retroposons, more than any other group, and as such are a great source to find shared retroposons,” Nilsson said of her research, published in PLoS Biology .
“The biggest surprise with our results came when we found support for a single origin of Australian marsupials. This can be interpreted as one single group of marsupials migrating from South America across Antarctica to Australia, to give rise to Australian marsupials.”
A furry little contradiction
While this research is based in Germany, Australian researchers are critical of the conclusions. Mike Archer from the University of New South Wales told ABC Science it ignores previously published data which suggest the migration from South America to Australia was "not just a one-way highway, it was a super two-way highway.”
Archer’s evidence lies in the diminutive Dromiciops gliroides, a secretive marsupial commonly known as monito del monte or ‘little mountain monkey’, that lives in the rainforests of Chile and Argentina.
Proven in previous studies to be a distant relative of Australia's earliest known marsupial, Djarthia murgonensis, Archer argues it’s more likely that the Dromiciops originated in Australia and migrated to South America.
"The authors are failing to recognise that Australia has been the centre of [marsupial] evolution," Archer said.
Dromiciops’ mysterious journey
But perhaps the marsupials’ travelling between continents was even more fluid, as suggested by Jenny Graves from the Australian National University in Canberra. “The Dromiciops looks exactly like marsupials you find in Australia, and it’s got the same chromosomes, so we were thinking, 'What’s it doing in South America?'"
“Maybe it arrived at Australia with the rest of them and then wandered back to South America. But on the other hand, possibly it was left behind.”
Katherine Thompson, also from the ANU, originally characterised five of the sequences used in the research, including some of the tammar wallaby markers, Graves said. “It’s great to see some of the sequences we pulled out being put to good use,” she added.
