DNA study of old museum exhibits to tell migration story of native rodents
Scientists study the DNA of 180-year-old museum exhibits to tell the ancient 8.5-million-year-long origin story of our native rodents
READING LEVEL: ORANGE
Scientists have studied the DNA* of 180-year-old museum exhibits to tell the 8.5-million-year-long story of Australia’s native rodents*.
The star of the story is the pregnant rat who began this epic* tale by rafting across treacherous* seas from Southeast Asia to New Guinea.
Australia has more than 60 species of native rodents not found anywhere else in the world, but they are becoming extinct faster than any other group of mammals in Australia. There are 11 species on the mainland* declared extinct since 1788 and many more species are critically* endangered.
Knowing more about those already or almost extinct will help us protect the remaining species.
Led by Australian National University (ANU) evolutionary* biologist* Dr Emily Roycroft, Australian scientists mapped the DNA of more than 150 species of native rodents from Australia, New Guinea and Melanesian* islands. This mapping helped them create a rodent family tree to understand how different species are related and how and when they spread across the Pacific region.
“By studying their DNA, we know that native rodents from New Guinea and Australia are close relatives to rodents in Southeast Asia,” Dr Roycroft told Kids News.
“Geologists who study how the Earth has changed over millions of years (an area of science called plate tectonics), also know that Southeast Asia has never been connected to New Guinea or Australia by land.
“To get across the treacherous ocean between Asia and New Guinea, we think that the ancestor of native rodents used a piece of driftwood like a raft. Rodents seem to be very talented rafters – they’ve also migrated overwater from New Guinea into the Solomon Islands and Maluku Islands.”
Dr Roycroft said rodents were a fascinating but under-appreciated evolutionary group.
“There are over 150 species in Australia and New Guinea that aren’t found anywhere else in the world, like the rakali – or (so-called) water rat – that’s often seen swimming around Canberra’s lakes,” Dr Roycroft said.
“Until now, we’ve known very little about the evolution and origin of native rodents, especially species in New Guinea.”
The scientists collected DNA from museum exhibits and combined this genetic information with genetic information from modern specimens* to understand how different species of native rodents are related.
“One specimen of Guadalcanal rat from the Solomon Islands dates back to the 1880s, and the species hasn’t been seen since,” Dr Roycroft said. “It’s listed as critically endangered, and very possibly already extinct. We were curious to revisit these old specimens using modern technology.
The study shows that native rodents are very good at colonising* new areas. When they first arrived in Australia they adapted to a lot of new environments – including the arid* desert.
Knowing more about native rodents’ history will help us protect surviving species from extinction.
“Native rodents have a deep intrinsic* value in our ecosystems. They’re ecosystem engineers; they aerate* soil via burrowing and foraging* and they help to disperse* seeds and fungal spores*,” she said.
“They also play a role in food webs as an important source for native predators, and in turn they feed on plants, fungi and smaller animals themselves.
“But they also have the highest extinction rate of any Australian mammal group, due to extreme habitat loss and introduced predators. If we lose even one native species, it can throw off the balance in an ecosystem.”
The research is published in the journal Current Biology.
RAT RACE TO AUSTRALIA
– 8.5 million years ago: Rodents migrated from the Philippines to New Guinea, most likely by a single pregnant female floating on a raft of driftwood.
– 5 million years ago: The Earth’s tectonic plates shifted, causing what geologists call the New Guinea uplift (creating New Guinea’s mountains). The uplift formed a continent called Sahul, which included a land bridge between New Guinea and Australia.
– Before 8000 years ago: Rodents migrated backwards and forwards between Australia and New Guinea in several waves when sea levels were low enough to expose a land bridge. One of the last times this was possible was about 10,000-8000 years ago during an ice age.
– 1788-2022: At least 11 native rodent species became extinct on the Australian mainland due to land clearing and introduced predators such as foxes and cats.
GLOSSARY
- DNA: genetic material in cells of living things that provide instructions about how to develop, live and reproduce
- rodents: group of mammals that has a pair of continuously growing top and bottom teeth
- epic: very long task, story or poem
- treacherous: presenting hidden or unpredictable dangers
- mainland: main land mass, not including nearby islands
- critically: to an extreme degree
- evolutionary: relating to evolving or changing over time
- biologist: scientist of living things
- Melanesian: group of Pacific Islands called Melanesia that are from New Guinea to Tonga
- specimens: samples for scientific study
- colonising: establishing a population in an area
- arid: dry
- intrinsic: necessary part of; belonging to; essential
- aerate: put air into
- foraging: searching for food
- disperse: spread over a wide area
- spores: the single cells that fungi makes to reproduce and make more fungi
EXTRA READING
Extinct native mouse found living on WA island
Rat wins top bravery award for landmine work
Spotlight on backyard threatened species
Tech exists to resurrect Tassie tiger
QUICK QUIZ
- How old is the origin story of Australia’s native rodents?
- How old are the museum exhibits providing the study’s DNA samples?
- Where did the pregnant rat travel from and to?
- How many species of native rodent does Australia have that are not found anywhere else?
- How do native rodents operate as ecosystem engineers?
LISTEN TO THIS STORY
CLASSROOM ACTIVITIES
1. Food web
Sketch a diagram to show how native rodents fit into the food web. Include any information that can be gathered from the news story such as what they eat, what eats them, and how their activities contribute to the regeneration of food sources.
Time: allow 20 minutes to complete this activity
Curriculum Links: English; Science
2. Extension
There are lots of interesting words featured in this story’s glossary. Choose three words that are least familiar to you. Practise spelling these words. Write each of them in a new sentence that is not related to this news story. Challenge yourself to use them in conversation in the next week.
Time: allow 15 minutes to complete this activity
Curriculum Links: English
VCOP ACTIVITY
1. Summarise the article
A summary is a brief statement of the main points of something. It does not usually include extra detail or elaborate on the main points.
Use the 5W & H model to help you find the key points of this article. Read the article carefully to locate who and what this article is about, and where, when, why and how this is happening. Once you have located this information in the article, use it to write a paragraph that summarises the article.
Time: allow 25 minutes to complete this activity
Curriculum Links: English; Science