World-first study reveals the mysteries of the desert-dwelling marsupial mole
Hidden beneath the dunes, a mysterious creature glides through the sand.
This isn’t one of the giant worms of Arrakis in Frank Herbert’s science fiction epic Dune. Rather, it is an enigmatic and small mammal found only in the deserts of Australia: the marsupial mole.
There are two related species of the marsupial mole.
Notoryctes typhlops, or southern marsupial mole, is found in the deserts of central and southern Australia. It is true called it jaritjari by the local indigenous Aṉangu peoples.
Notoryctes caurinus, or the northern marsupial mole, is found in the deserts of northwestern Australia. It is also called kakarratul by the local indigenous Martu people. Until recently, these elusive animals were virtually impossible to study.
But our recent study in Science Advances has finally begun to unravel the basis of their incredible ‘desert power’.
Rarely observed
Marsupials are small, about the length of a pencil, and weigh between 40 and 70 grams.
Marsupial moles are found in the deserts of central and southern Australia
They are small, about the length of a pencil, and weigh between 40 and 70 grams
They have a tubular body, yellow hair, and limbs that barely extend from the sides.
than building permanent tunnels like their namesakes in the Northern Hemisphere, they ‘swim’ through the loose sand of the Australian deserts.
The subterranean lifestyle of marsupials, together with the vastness of the deserts they inhabit, means they are rarely sighted. In fact, there are only a handful of observations per decade.
New technologies, new insights
New DNA technologies could offer a glimpse into the lives of cryptic species like the marsupial mole, which cannot be studied effectively in the wild.
To achieve this, our team collaborated with the Australian biological tissue collection at the South Australian Museum to acquire two small tissue samples frozen from a southern marsupial mole more than a decade ago.
From this we extracted extremely long DNA fragments needed to produce a genome assembly. This is a digital representation of each base or ‘letter’ that makes up the marsupial’s genetic code.
Because DNA contains both the instructions for creating an organism’s traits and a record of its evolutionary history, we were able to gain remarkable insights into this cryptic species.
Unique adjustments
Marsupial moles have a variety of unique adaptations that help them survive in their harsh environment. For example, their eyes are small and located under their skin, making them functionally blind.
By comparing the sequences of eye genes with those of related marsupials, we were able to show that marsupials first lost genes crucial for the eye lens. This probably happened because a clear image underground is not that important.
This was followed by genes for color-sensitive cone cells in the retina. After the eye lost significant function, the last genes to be knocked down were those active in rod cells, which are important in low light.
In surface-dwelling mammals, these changes would likely be harmful. But by happening in the right order, the gradual breakdown of eye genes allowed the marsupial mole’s ancestors to gradually change without harming their fitness.
This is a wonderful illustration of how both adaptations and disorders can share a similar genetic basis, with the boundary between them being formed by their context.
A new study has finally begun to unravel the basis of the incredible ‘desert power’ of marsupial moles
Other features
Sequencing the genome allowed us to study other traits of marsupials.
For example, we showed that a key gene involved in testicular failure during puberty is also likely to be knocked down in this species. This may help explain why male marsupials do not have a scrotum and have their testes in their abdominal wall.
We also discovered that marsupials have two copies of a gene that codes for hemoglobin – the molecule that carries oxygen in red blood cells. This is important because sand has low oxygen content and poor air movement.
Furthermore, this duplicated hemoglobin gene is typically used in newborn mammals.
A marsupial’s pouch is already an oxygen-poor environment, so marsupial moles had to develop ways to keep their young from suffocating. It can help to have more hemoglobin.
Tracing the evolutionary heritage of the mole
For years, the marsupial mole’s strange, specialized traits have frustrated attempts to determine exactly who its closest relatives actually are. But by sequencing its genome, we have been able to trace its evolutionary heritage.
To do this, we examined a special type of DNA sequence called retrotransposons.
These are short stretches of DNA that can make copies of themselves that are randomly inserted into an animal’s genome and passed on from generation to generation.
Our research has shown that marsupials are a sister group bandicoots And Bilbieswith carnivorous marsupials such as the Tasmanian devil are distant cousins.
Long-term decline
Virtually nothing is currently known about the population health of marsupial moles. However, Deserts are among the ecosystems most threatened by climate change.
That’s why we also tried to gather the first insights into how marsupial populations have changed over time.
Using patterns of genetic diversity across the marsupial mole’s genome, we have been able to show that they likely experienced a long-term decline in effective population size that began about 70,000 years ago. This is consistent with historical changes during the last ice age, suggesting that the decline was due to climate change rather than human action.
It is unclear how exactly the genetic diversity lost over tens of thousands of years will affect the marsupial mole’s ability to continue its record of adapting to extreme environments.
However, these findings highlight that new, more extensive efforts to study marsupials using genetic methods may be needed to ensure they are not lost to the sands of time like many other Australian mammals.