̽��ֱ�� of Cambridge - Máire Ní Leathlobhair

Ancient American dogs almost completely wiped out by arrival of European breeds

cjb250 — Thu, 05 Jul 2018 18:00:52 +0000

But one close relative of these native dogs lives on in an unexpected place – as a transmissible cancer whose genome is that of the original dog in which it appeared, but which has since spread throughout the world.

Using genetic information from 71 archaeological dog remains from North America and Siberia, an international team led by researchers at the ̽��ֱ�� of Oxford, ̽��ֱ�� of Cambridge, Queen Mary ̽��ֱ�� of London, and Durham ̽��ֱ�� showed that ‘native’ (or ‘pre-contact’) American dogs, which arrived alongside people over 10,000 years ago and dispersed throughout North and South America, possessed genetic signatures unlike dogs found anywhere else in the world.

Comparison of ancient and modern American dog genomes, however, demonstrated that these pre-contact American dogs rapidly disappeared following the arrival of Europeans and left little to no trace in modern American dogs.

Senior lead author Dr Laurent Frantz from Queen Mary ̽��ֱ�� and the Palaeogenomics & Bio-Archaeology Research Network (Palaeo-BARN) at Oxford said: “It is fascinating that a population of dogs that inhabited many parts of the Americas for thousands of years, and that was an integral part of so many Native American cultures, could have disappeared so rapidly. Their near-total disappearance is likely due to the combined effects of disease, cultural persecution and biological changes starting with the arrival of Europeans.”

Professor Greger Larson, Director of the Palaeo-BARN at Oxford and senior author of the study, said: “This study demonstrates that the history of humans is mirrored in our domestic animals. People in Europe and the Americas were genetically distinct, and so were their dogs. And just as indigenous people in the Americas were displaced by European colonists, the same is true of their dogs.”

By comparing the ancient and modern genomes, the researchers confirmed that the earliest American dogs were not descended from North American wolves, but likely originated in Siberia, crossing into the Americas during early human migrations.

Lead archaeologist Dr Angela Perri from Durham ̽��ֱ��, co-first author on the study, added: “Archaeological evidence has long suggested that ancient dogs had a dynamic history in the Americas, but the fate of these pre-contact dogs and their relationship to modern American dog populations was largely unknown. Our study confirms that they likely originated in Siberia, crossing the Bering Strait during initial human migrations.”

“In fact, we now know that the modern American dogs beloved worldwide, such as Labradors and Chihuahuas, are largely descended from Eurasian breeds, introduced to the Americas between the 15th and 20th centuries.”

Intriguingly, the study revealed a close link between the genomes of the pre-contact dogs, as the researchers refer to them, and those derived from canine transmissible venereal tumours (CTVT). CTVT is a contagious genital cancer that is spread between dogs by the transfer of living cancer cells during mating. CTVT originated from the cells of a single dog, known as the ‘CTVT founder dog’, that lived several thousand years ago. Remarkably, the research revealed that the dog that first spawned CTVT was closely related to American pre-contact dogs. Overall the results indicate that this cancer, now found worldwide, possesses a genome that is the last remaining vestige of the dog population that was once found all across the Americas.

“It’s quite incredible to think that possibly the only survivor of a lost dog lineage is a tumour that can spread between dogs as an infection,” added Maire Ní Leathlobhair, co-first author, from the Department of Veterinary Medicine at the ̽��ֱ�� of Cambridge. “Although this cancer’s DNA has mutated over the years, it is still essentially the DNA of that original founder dog from many thousands of years ago.”

Co-author and zooarchaeologist Professor Keith Dobney from the ̽��ֱ�� of Liverpool, who co-directs the dog domestication project with Professor Larson added “This is yet another new and exciting finding from our combined genetic and archaeological research, which continues to challenge and illuminate our understanding of the history of the first and most iconic domestic animal.”

̽��ֱ��research was largely funded by Wellcome, the Natural Environment Research Council, and the European Research Council.

Reference
Ní Leathlobhair, M, Perri, AR, Irving-Pease, EK, Witt, KE, Linderholm, A, et al. ̽��ֱ��Evolutionary History of Dogs in the Americas. Science; 6 July 2018; DOI: 10.1126/science.aao4776

̽��ֱ��arrival of Europeans to the Americas, beginning in the 15th century, all but wiped out the dogs that had lived alongside native people on the continent for thousands of years, according to new research published today in Science.

It’s quite incredible to think that possibly the only survivor of a lost dog lineage is a tumour that can spread between dogs as an infection

Maire Ní Leathlobhair

Del Baston (courtesy of the Center for American Archeology)

Ancient dog burial

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A shaggy dog story: ̽��ֱ��contagious cancer that conquered the world

cjb250 — Mon, 16 May 2016 23:01:16 +0000

‘Canine transmissible venereal tumour’ (CTVT) is a cancer that spreads between dogs through the transfer of living cancer cells, primarily during mating. ̽��ֱ��disease usually manifests as genital tumours in both male and female domestic dogs. ̽��ֱ��cancer first arose approximately 11,000 years ago from the cells of one individual dog; remarkably, it survived beyond the death of this original dog by spreading to new dogs. ̽��ֱ��cancer is now found in dog populations worldwide, and is the oldest and most prolific cancer lineage known in nature.

In a study published today in the journal eLife, an international team led by researchers at the ̽��ֱ�� of Cambridge studied the DNA of mitochondria – the ‘batteries’ that provide cells with their energy – in 449 CTVT tumours from dogs in 39 countries across six continents. Previous research has shown that at occasional points in history, mitochondrial DNA has transferred from infected dogs to their tumours – and hence to tumour cells in subsequently-infected dogs.

In the new study, the researchers show that this process of swapping mitochondrial DNA has occurred at least five times since the original cancer arose. This discovery has allowed them to create an evolutionary ‘family tree’, showing how the tumours are related to each other. In addition, the unusual juxtaposition of different types of mitochondrial DNA within the same cell unexpectedly revealed that cancer cells can shuffle or ‘recombine’ DNA from different mitochondria.

“At five distinct time-points in its history, the cancer has ‘stolen’ mitochondrial DNA from its host, perhaps to help the tumour survive,” explains Andrea Strakova, from the Department of Veterinary Medicine at the ̽��ֱ�� of Cambridge, co-first author of the study. “This provides us with a set of unique genetic tags to trace how dogs have travelled the globe over the last few hundred years.”

In the evolutionary ‘family tree’, the five main branches are known as ‘clades’, each representing a point in history when mitochondria transferred between dog and tumour. By mapping tumours within these clades to the geographical location where they were found, the researchers were able to see how the cancers have spread across the globe. ̽��ֱ��distance and speed with which the clades have spread suggests that the dogs commonly travelled with human companions, often by sea.

One branch of the CTVT evolutionary tree appears to have spread from Russia or China around 1,000 years ago, but probably only came to the Americas within the last 500 years, suggesting that it was taken there by European colonialists. Conquistadors are known to have travelled with dogs – contemporary artworks have portrayed them both as attack dogs and as a source of food.

Image: 1598 fictional engraving by Theodor de Bry supposedly depicting a Spaniard feeding Indian children to his dogs. Wikipedia

̽��ֱ��disease probably arrived in Australia around the turn of the twentieth century, most likely imported inadvertently by dogs accompanying European settlers.

One of the most surprising findings from the study related to how mitochondrial DNA transfers – and mixes – between the tumour and the host. ̽��ֱ��researchers found that mitochondrial DNA molecules from host cells that have migrated into tumour cells occasionally fuse with the tumour’s own mitochondrial DNA, sharing host and tumour DNA in a process known as ‘recombination’. This is the first time this process has been observed in cancers.

Máire Ní Leathlobhair, the study’s co-first author, explains: “Mitochondrial DNA recombination could be happening on a much wider scale, including in human cancers, but it may usually be very difficult to detect. When recombination occurs in transmissible cancers, two potentially very different mitochondrial DNAs – one from the tumour, one from the host – are merging and so the result is more obvious. In human cancer, the tumour’s mitochondrial DNA is likely to be very similar to the mitochondrial DNA in the patient’s normal cells, so the result of recombination would be almost impossible to recognise.”

Although the significance of mitochondrial DNA recombination in cancer is not yet known, its discovery is now leading scientists to explore how this process may help cancer cells to survive – and if blocking it may stop cancer cells from growing.

Dr Elizabeth Murchison, senior author of the study, said: “ ̽��ֱ��genetic changes in CTVT have allowed us to reconstruct the global journeys taken by this cancer over two thousand years. It is remarkable that this unusual and long-lived cancer can teach us so much about the history of dogs, and also about the genetic and evolutionary processes that underlie cancer more generally.”

̽��ֱ��research was funded by the Wellcome Trust, the Leverhulme Trust and the Royal Society.

Reference
Strakova, A et al. Mitochondrial genetic diversity, selection and recombination in a canine transmissible cancer. eLife; 17 May 2016; DOI: 10.7554/eLife.14552

A contagious form of cancer that can spread between dogs during mating has highlighted the extent to which dogs accompanied human travellers throughout our seafaring history. But the tumours also provide surprising insights into how cancers evolve by ‘stealing’ DNA from their host.

It is remarkable that this unusual and long-lived cancer can teach us so much about the history of dogs, and also about the genetic and evolutionary processes that underlie cancer more generally

Elizabeth Murchison

Mitochondrial genetic diversity, selection and recombination in a canine transmissible cancer

̽��ֱ�� of Cambridge

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