From redundant eyes and internal testicles to backwards pouches, marsupial moles have some pretty bizarre traits. And their elusive nature – living in the deep deserts of Australia – only adds to their mysterious allure.
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However new research into the genome of the marsupial mole – known as itjaritjari to Indigenous Aṉangu people - has solved some of the mysteries behind its distinctive appearance and lifestyle.
What are marsupial moles?
These golden-haired creatures live in the deserts of Australia, ‘swimming’ through loose sands using specialised 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.
By extracting DNA from a preserved tissue sample, the Melbourne team along with collaborators at La Trobe University and the University of Connecticut, mapped nearly all the chemical ‘letters’ that record the mole's evolutionary past and lays out instructions for producing its most distinctive traits.
The team then used this genome to compare marsupial mole genes to those of its distant relatives living above ground.
By examining eye genes shared among all mammals, the study 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.
The study, published in Science Advances, also revealed the species possessed an additional gene for haemoglobin, the protein that carries oxygen around the body, and that could be an adaptation to living underground in low-oxygen conditions.
As for their absent scrotum, the team found the marsupial moles had lost or mutated genes involved in the descent of the testes. This may have evolved “presumably to minimise drag when moving through sand/earth,” the authors write.
The marsupial mole's 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.
The research team employed an innovative approach to resolving this, examiningretrotransposons – sometimes called ‘jumping genes’.
As the name implies, these genes can move around the genome and do so by copying and then pasting themselves into a different region. “However, the same gene is very unlikely to jump at random into the same region in two different species,” as lead researchers Dr Charles Feigin, Dr Stephen Frankenberg, and Professor Andrew Pask explain. “This makes shared transposon insertions a very reliable indicator of shared ancestry.”
This meant the researchers could show that marsupial moles’ closest relatives turn out to be Australia’s bandicoots and bilbies, with their common ancestor existing around 60 million years ago.
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Future of the marsupial mole
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.
The study found it was much more diverse than it is today.
Beginning around 70 thousand 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.
The study 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," the Melbourne researchers said.
"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."
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Illustration by Lydekker, Richard, Public domain, via Wikimedia Commons