An artist's impression of a Sardinian dhole

The Sardinian dhole lived on Sardinia and Corsica until becoming extinct after the arrival of humans. Image © Mariomassone, licensed under CC BY 4.0 via Wikimedia Commons.

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Sardinia was once home to a corgi-sized canine

A corgi-sized canine once roamed Mediterranean islands, hunting small prey like birds and pika. 

The arrival of humans may have provided the final nail in the coffin for this bite-size predator, which had low genetic diversity after being confined to Sardinia and Corsica by rising seas. 

The evolutionary history of an extinct species of canid has been revealed, with suggestions that people may have helped wipe it out. 

The Sardinian dhole was a small dog-like animal that lived on the islands of Sardinia and Corsica for thousands of years before vanishing around 10,000 years ago. Researchers analysed DNA from a fossilised specimen and found it is a separate species from all living dogs and wolves alive today.  

It also had low genetic diversity, which researchers believe is likely due to its isolation on the islands for hundreds of thousands of years. The arrival of humans may have left it unable to adapt quickly enough to survive, leading to its extinction. 

Dr Selina Brace, an ancient DNA specialist at the Museum who was not involved with the study, says the researchers had done 'amazingly well.' 

'It's very impressive that they got a sample from a 20,000-year-old specimen in this region,' she says. 'Heat's not the friend of ancient DNA so to obtain a whole genome from an extinct species is a standout achievement. 

The research, led by Danish scientists, was published in Current Biology.

The interior of Neptune's cave on Sardinia

Caves can preserve the integrity of ancient remains due to their specific microclimate.  Image © Shutterstock / Ignazio_Arena

Small wonder 

The Sardinian dhole was first discovered in the 1850s, with a number of preserved bones kept in European museums.  

Fossil evidence suggests it was a hunter of small prey and scavenger, as its jaws were likely too weak to tackle larger animals. It probably ate small rabbit-like mammals called pika as well as birds on the islands. 

Its small size resulted from an evolutionary process known as insular miniaturisation. This is where a lack of resources and competitors on islands can result in species shrinking in size. As a result, the Sardinian dhole is estimated to have weighed around 10 kilograms, which is roughly the same as a corgi. 

It shares its common name with the dhole, a distinct species of wild dog that is found in India and parts of Southeast Asia. However, while they share a name, different studies dispute how closely related the extinct and living dholes were. 

The researchers decided to investigate the genetics of the Sardinian dhole found in Corbeddu cave on the island, using bone samples taken from a skull bone.  

'Ancient DNA isn't necessarily about age,' Selina says. 'As soon as a living thing dies, its DNA begins to break down and fragment. This makes it more difficult to extract it and sequence the genome. If the fragments are too small, they can't be put back together again. 

'To preserve this DNA, the environment is key. A hotter environment causes DNA to fragment more quickly and for greater degradation in the sequence, so preservation in caves, as in this case, helps to preserve its integrity for longer. 

'The material being sampled also affects preservation. This study used the petrous bone, which is really interesting as it is the densest in the body. That's why it is used in ancient DNA studies, as it can better protect DNA from the environment and give us a better quality sample.' 

The samples were carbon dated to find out the age of the specimen, while its genetics were tested for the relationships with other species. 

An Asiatic dhole in woodland

The Sardinian and Asiatic dholes are estimated to have diverged from each other around 885,000 years ago.  Image © Shutterstock / Vinod V Chandran

Doomed to extinction? 

The Sardinian dhole bones revealed that the individual was a female and probably died around 21,000 years ago. 

Though the DNA was damaged, the researchers were able to piece together the family tree of the species in relation to other living canids. Their analysis found that the Sardinian dhole is most likely a close relative of the Asian dhole, as well as being a sister taxa to Canis, which contains all living wolves, dogs and coyotes.  

Their findings also suggest that the Sardinian dhole shared a number of genes with grey wolves than expected, which suggest the possibility of either interbreeding or that other wolf species may have an unknown canid ancestor. 

The genetic findings also give clues about how the species may have evolved on the island. It is presumed the ancestor of the dholes arrived on Sardinia and Corsica between three and five million years ago on a land bridge that no longer exists.  

While the species was cut off from the mainland as the land bridge disappeared, the researchers found evidence that some ancestors of the Asian and Sardinian dhole may have crossed the sea in this period when sea levels fell periodically. This continued for hundreds of thousands of years until they were permanently separated between 510,000 and 310,000 years ago. 

Its genetic distribution suggests that the species declined in number, leading to a genome with low diversity. While some findings can be made confidently from this specimen alone, Selina says that others will require other Sardinian dholes to be studied. 

'Once you have obtained the DNA, you can use it to produce different trees to investigate its relationship with other species, such as gene flow and inbreeding,' she says. 'However, in this case, you need to be a bit careful about making findings based on inbreeding, as it is a population measure and it could just be an anomaly in this individual.' 

Researchers compared the diversity of the Sardinian dhole genome to those of mountain gorillas, whose populations have shrunk relatively rapidly as a result of human persecution. 

The researchers suggest this could possibly suggest that humans could have contributed to the Sardinian dhole's extinction after arriving on the island some 20,000 years ago. However, other causes, such as inbreeding and loss of genetic diversity, may have already set the species on the road to extinction, with our ancestors perhaps only accelerating the inevitable.