Scientists are discovering the deepest evolutionary secrets of Australia’s marsupial mole

Marsupial moles are perhaps Australia’s most bizarre mammals. Known as “itjaritjari” to the Indigenous Aṉangu people and featuring prominently in their tales, the marsupial mole is rarely observed, making any sighting a rare event.

Now, our team, led by Dr. Stephen Frankenberg and Professor Andrew Pask, has begun to unearth some of the marsupial mole’s deepest evolutionary secrets by studying its genome for the first time.

Adapting to a life down under

Marsupial moles live in the deep deserts of Australia, making their way not by digging permanent tunnels but by “swimming” through loose sands using specialized forelimbs.

This lifestyle is so vital to their existence that they’ve had to adapt in remarkable ways.

They are nearly blind, with only vestigial eyes beneath the skin on their face, and lack a scrotum, keeping their testes in their abdomen.

Being marsupials, the females have a pouch, but it has evolved to face backwards to stop it filling with sand.

Even breathing is a challenge underground, so marsupial moles have also had to evolve to survive in low-oxygen conditions.

Incredibly, many of these adaptations are shared with the “true” moles found in Africa, Eurasia and North America, representing a striking example of convergent evolution.

Exploring below the surface

By extracting DNA from an incredibly precious preserved tissue sample, our team, along with our collaborators at La Trobe University and the University of Connecticut, mapped nearly all the chemical “letters” that record its evolutionary past and lays out instructions for producing its most distinctive traits.

Team members from here and the University of Utah then used this genome to compare marsupial mole genes to those of its distant relatives living above ground.

Our findings, now published in Science Advances, were remarkable.

By examining eye genes shared among all mammals, we showed that degeneration of the marsupial mole’s eyes occurred in stages, with genes important for the lens going first, followed by the “rods and cones”—the light-sensing cells found in the retina.

We also showed that marsupial moles have an extra gene for hemoglobin, the protein that carries oxygen around the body in red blood cells and that a key gene in testicular descent—RXFP2—is “broken” in this species, giving us an explanation for its internal testes.

Figuring out the family tree

Because of its strange traits and the lack of robust DNA evidence, the marsupial mole’s relationships with other marsupials have been extremely difficult to figure out.

Our colleagues at the University of Münster employed an innovative approach to resolving this, examining retrotransposons—sometimes called “jumping genes.”

These genes copy themselves repeatedly into different regions of the DNA at random. However, the same gene is very unlikely to jump at random into the same region in two different species.

This makes shared transposon insertions a very reliable indicator of shared ancestry.

And this meant we could show that marsupial moles’ closest relatives turn out to be Australia’s bandicoots and bilbies, followed by the carnivorous marsupials like Tassie devils.

A species in decline?

As part of the same research, collaborators at the University of Münster and La Trobe scanned the marsupial mole genome to learn more about how these processes have influenced genetic diversity in this species.

We found it was much more diverse than it is today.

Beginning about 70,000 years ago though, the species entered a long, slow decline.

Interestingly, this decline seems to have begun more than 5,000 years before the arrival of humans in Australia and at least 30,000 years before they settled in regions near the marsupial mole’s habitat.

This suggests Aboriginal peoples had little impact on this cryptic species.

Rather, we found that this decline corresponds with a period of cooler temperatures and lower sea levels, which implicates climatic changes as the reason.

Genetic diversity is vital for a species’ health and its ability to adapt in a changing world.

Our work shows that just because the marsupial mole is often out of sight, it shouldn’t stay out of mind. For its future, we need new efforts to study the population health and stability of this sneaky little Australian mammal.