Part of SRSU Assistant Professor’s research work on the cover of Science magazine.

Donkeys generally appear to us as stubborn and not particularly fast animals.

However, a new study published in the September 9 issue of the journal Science now shows that donkeys spread like wildfire from Africa about 4,500 years ago, reaching Europe and Asia within a few centuries.

This shows the key role donkeys played in earlier human societies, particularly as pack animals mobilizing people, culture, and goods across arid deserts and steep mountains.

Surprisingly, where and when donkeys were first domesticated has long been a scientific mystery. Archaeological finds, as well as textual and iconographic evidence, have suggested the vast region of Northeast Africa as a possible source.

But they also pointed to regions outside of Africa, possibly in the Arabian Peninsula, or even further away in Mesopotamia.

Previous work aimed at tracing the evolutionary history of donkeys based on their genetics could not find significant support for a candidate region.

“We decided to sequence the genome of donkeys living in regions previously overlooked,” explained Ludovic Orlando, CNRS research director at the Center for Anthropobiology and Genomics of Toulouse (CNRS / University of Toulouse III Paul Sabatier) and senior Author of the study in the press release. “This should reveal important missing pieces of the puzzle.”

This provided the research team, which consists of 49 scientists from 37 laboratories around the world, with the most comprehensive genome panel of donkeys. However, mapping the genetic diversity of present-day donkeys may not have been sufficient, as modern breeding and trade may have exchanged animals across very distant regions. Therefore, researchers should also characterize the genomes of donkeys that lived in the past, using state-of-the-art technologies in the study of ancient DNA.

dr Laura Patterson Rosa, assistant professor of animal and equine sciences at Sul Ross State University, was part of the team that analyzed the donkeys’ genome as part of the study.

To the efforts of Dr. Patterson Rosa included tasting a unique South American donkey breed, the Pega donkey, which has been heavily selected since the colonization of America for its smooth locomotion – as a “gait” donkey breed – and its endurance. World and historical comparative genomic analysis has shown that the written historical accounts of the origin of this breed may not be entirely accurate. In addition, the results have elucidated high levels of genomic inbreeding, which is of concern as the maintenance of the Pega donkey may require planned outcrossing to maintain health and population diversity.

“Modern donkeys living in different regions of the world show quite strong genetic differences, especially between the African, European and Asian continents,” explained Dr. Evelyn Todd, first author of the study, in the press release.

In addition to striking geographic differences, the team found that the timing of separation between the different populations followed a clear trend, starting first in Africa and spreading to Eurasia and Asia. The researchers report an African origin around 7,000 years ago, around a time when the once verdant Sahara region was becoming one of the driest deserts on earth. They estimate that donkeys spread out of Africa at least 4,500 years ago and expanded rapidly both eastward into Asia and westward into Europe within 1,000 years at most.

The expansion was not only in one direction, but also returned to Africa. For example, as early as Roman times, donkeys were exchanged between Europe and Africa across the Mediterranean, according to the study. While this exchange went both ways and continued after the collapse of the Roman Empire, it left the most important genetic footprint in modern donkeys from West Africa.

Ancient genomes securely provide localized time points that have helped researchers track the spread of donkeys around the world. They also revealed the presence of previously unknown genetic lines. 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, Central Asia, and East Asia.

In addition, the researchers show that wild donkey relatives also introduced a fraction of their genes to different regions of the world.

For Evelyn Todd, “This likely reflects the free-range nature of local donkey populations in some regions of Africa and the Arabian Peninsula.”

The study clearly shows 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 tracing global patterns of donkey management techniques. They found a mule-breeding center at Boinville-en-Woëvre, a second- to fifth-century Roman site from northern France. There, breeders seem to have produced particularly inbred families of giant donkeys at a time when mules provided the labor for the shipment of military equipment and goods across an empire that stretched thousands of miles. Mating between these huge donkeys and horse females enabled breeders to produce prized sterile mules.

Here, the genetic evidence echoes the texts of Roman writers, who described how the selective breeding of animals of exceptional stature was common practice and a lucrative business even then.

“That’s the beauty of ancient DNA, providing data that allows us to test hypotheses from other classic historical sources,” Orlando concluded.

The genetic study went a step further: the limited presence of horses in Boinville-en-Woëvre suggests that either female horses for mating or donkey breeders with their huge males visit the surrounding farms. A different kind of journey, admittedly over a more limited region than that which took their ancestors outside of Africa thousands of years ago, but which nonetheless helped build the mighty Roman Empire.

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