Australia’s rodent immigrants – one of the greatest successes in mammal evolution

Paucidentomys vermidax
Paucidentomys vermidax, the only rodent with no molars. A muroid rodent native to the island of Sulawesi that evolved a specialised diet of worm eating.
Image: Dr Kevin Rowe, Museum Victoria
Source: Museum Victoria

Media contact: Alex Dook
adook@museum.vic.gov.au

A new study has used the genetic sequences of 300 different species to map the amazing evolutionary progress of Australia's native rodents.

Co-author of the study, Dr Kevin Rowe, Senior Curator of Mammals at Museum Victoria, said the research had revealed "one of the greatest immigration success stories in mammalian evolution".

Australian rodents immigrated naturally to this continent in two events: one approximately five million years ago, and another approximately one million years ago. Every rodent species native to Australia today can trace its ancestry back to one of these two founding groups of immigrants.

"When rodents arrived on the Australian continent, they underwent a species explosion, diversifying faster than they had previously. This spectacular diversification resulted in the ecologically diverse native rodents we see in Australia today, including aquatic rats, arid-adapted hopping mice, and grass-eating lemming-like rats," Dr Rowe said.

A central question for evolutionary biology is why some groups have more species than others. "Certainly there is something exceptional about muroid rodents," said Dr Rowe, noting that since their split from dipodoid rodents 45 million years ago, the Muroidea have diversified into a large super-family comprising over 1500 species. They now make up nearly one third of all mammal species, including all mice, rats, hamsters, and gerbils. In contrast, dipodoid rodents have diversified into only 50 species over that same time period.

One hypothesis to explain the exceptional diversity of muroids is their expansion around the world.

"Ecological theory suggests that colonising new landmasses should come with advantages because of new ecological opportunities for diversification," said Dr Rowe. The study found, however, that only a few of the 31 continental immigration events resulted in an increase in diversification. The diversification of rodents following colonisation of Australia was one of these exceptions and was exceeded only by the diversification that followed muroid colonisation of South America.

The study "Ecological opportunity and incumbency in the diversification of repeated continental colonisations by muroid rodents" was written by John Schenk and Scott Steppan of the Florida State University, and Kevin Rowe of Museum Victoria.

Museum Victoria Public Relations contact:
Alex Dook, 8341 7141 / 0478 348 880, adook@museum.vic.gov.au

For all general public enquiries, contact the museum's Discovery Centre

Image Gallery

Lophiomys imhausi Mastacomys fuscus Pathways of continental Muroid immigration