SRSU assistant professor part of the research featured on the cover of “Science” magazine
Donkeys generally seem stubborn to us and not particularly fast.
Yet a new study published in the September 9 issue of the journal Science now reveals that donkeys spread like wildfire out of Africa around 4,500 years ago, reaching Europe and Asia in only a few centuries.
This demonstrates the key role donkeys played in past human societies, particularly as beasts of burden mobilizing people, culture and goods across arid deserts and rugged mountains.
Amazingly, where and when donkeys were first domesticated has remained a long-standing scientific mystery. Archaeological finds, as well as texts and iconographic evidence, have suggested the vast region of northeastern Africa as a possible source.
But they also pointed to areas outside of Africa, possibly the Arabian Peninsula, or even further into Mesopotamia.
Previous work aimed at tracking the evolutionary history of donkeys using their genetics found no significant support for any candidate region.
“We decided to sequence the genome of donkeys living in hitherto unknown regions”, specifies Ludovic Orlando, CNRS research director at the Center for Anthropobiology and Genomics of Toulouse (CNRS/Université Toulouse III Paul Sabatier) and author principal of the study. in the press release. “It was to reveal important missing pieces of the puzzle.”
This provided the research team, which includes 49 scientists from 37 laboratories around the world, with the most comprehensive panel of donkey genomes. However, mapping the genetic diversity of donkeys today may not have been sufficient as modern ranching and trade may have exchanged animals in very distant regions. Therefore, researchers must also characterize the genomes of donkeys that lived in the past, taking advantage of cutting-edge technologies in ancient DNA research.
Dr. Laura Patterson Rosa, an assistant professor of animal and equine science at Sul Ross State University, was part of the team that analyzed the genome of donkeys as part of the study.
Dr. Patterson Rosa’s efforts included sampling a unique South American breed of donkey, the Pega donkey, which was heavily selected for its smooth locomotion – as a “gaited” breed of donkey – and its endurance since the colonization of the Americas. Global and historical comparative genomic analysis has demonstrated that written historical accounts of the origin of this breed may not be entirely accurate. Additionally, the results shed light on the high genomic inbreeding, which poses a problem because conservation of the Pega donkey may require planned crossbreeding to maintain population health and diversity.
“Modern donkeys living in different parts of the world show quite strong genetic differences, particularly between the African, European and Asian continents,” said Dr. Evelyn Todd, first author of the study, in the press release.
In addition to the striking geographic differences, the team found that the timing of the split between different populations followed a clear pattern, starting first in Africa and spreading through Eurasia and Asia. Researchers report an African origin around 7,000 years ago, a time roughly close to when the once green region of the Sahara became one of the driest deserts on earth. They estimate that donkeys spread out of Africa at least 4,500 years ago and rapidly spread both east to Asia and west to Europe within 1,000 years or less.
The expansion not only followed one direction but also returned to Africa. For example, donkeys were already traded between Europe and Africa across the Mediterranean Sea in Roman times, according to the study. While these exchanges went both ways and continued after the collapse of the Roman Empire, they left the most significant genetic imprint in modern West African donkeys.
Ancient genomes provide securely located time points, which have helped researchers track the expansion of donkeys across the world. They also revealed the presence of previously unknown genetic lineages. One such lineage was found in the Levant around 2,000 years ago, but likely inhabited a much larger geographic region, as researchers have been able to identify traces of their genetic heritage in modern donkeys across Eastern Europe. East, Central Asia and East Asia.
Moreover, the researchers reveal that the parents of the wild donkeys also contributed a fraction of their genes to various regions of the world.
For Evelyn Todd, “This probably reflects the free-range management of local populations of donkeys in parts of Africa and the Arabian Peninsula”.
Clearly, the study reveals an important difference between the donkey and its close relative, the horse. Unlike horses, inbreeding in donkeys has not particularly increased in modern times, suggesting similar reproductive strategies today and in the past.
But the researchers went beyond simply tracking global patterns of donkey management techniques. They found a mule-breeding center at Boinville-en-Woëvre, a Roman site in northern France dating from the 2nd to 5th centuries. There, herders seem to have produced particularly inbred families of giant donkeys at a time when mules provided the labor to deliver military equipment and goods across an empire that spanned thousands of miles. kilometers. Mating between these giant donkeys and female horses has allowed breeders to produce highly prized sterile mules.
Here, the genetic evidence echoes the texts of Roman writers who described that the selective breeding of animals of exceptional stature was already common practice and a lucrative trade at the time.
“It’s the beauty of ancient DNA to provide data that allows us to test hypotheses from other classical historical sources,” Orlando concluded.
The genetic study went further: the limited presence of horses in Boinville-en-Woëvre suggests either equine females brought in for breeding, or donkey breeders visiting the surrounding farms with their giant males. A different type of journey, admittedly over a more limited region than that which brought their ancestors out of Africa thousands of years earlier, but which nonetheless contributed to building the mighty Roman Empire.