Eurasian horses a million years earlier than North American horses, DNA studies show. In new research, an international team of scientists sequenced and analyzed the mitochondrial and nuclear genomes of living and extinct horse horses (Equus spp.) To explore the possible effects of the Bering Land Bridge on genetic diversity and connectivity between a unique population. broad group.
They found that the Eurasian horse population initially separated from North America, their ancestral continent, about 1 million years ago; After this division, he identified two long-distance bi-directional spans of the Bering Land Bridge 875,000–625,000 and 200,000–50,000 years ago.
Many times during the Pleistocene, ancient horses crossed the Bering Land Bridge in both directions between North America and Asia. Many times during the Pleistocene, ancient horses crossed the Bering Land Bridge in both directions between North America and Asia.
The horses that lived in North America
Image credit: Julius Cissotoni. Paleontologists have long known that horses evolved and diversified in North America. One lineage, the cabaline horse (which includes domestic horses), spread to Eurasia over the Bering land bridge about 1 million years ago, and the Eurasian population began to deviate genetically from the horses that lived in North America.
The new study suggests that after the split, there were at least two periods in which the horses moved from continent to continent and interbred, such that the North American horse genome acquired Eurasian DNA segments and vice versa. “This is the first comprehensive look at the genetics of ancient horse populations on both continents,” said Dr. Alisa Varshina, a postdoctoral researcher at the University of California, Santa Cruz.
“With data from both mitochondrial and nuclear genomes, we were able to see that horses were not only spreading between continents, but were also swapping and swapping genes.” Dr. Varshina and her colleagues sequenced 78 new mitochondrial genomes from ancient horses found in Eurasia and North America.
Eurasian horses in North America
Combining those with 112 previously published mitochondrial genomes, she reconstructed a phylogenetic tree, a branch diagram showing how all the samples are related. With a location and approximate date for each genome, they were able to trace the movements of different ancient horse lineages.
We found a lineage of Eurasian horses in North America and vice versa, suggesting population movements between continents, Dr. Varshina said. With dated mitochondrial genomes we can see when the location changes occurred. The analysis showed a span of two periods between continents, both coinciding with the period in which the Bering Land Bridge would have been open.
In the Middle Pleistocene, shortly after the divergence of the two dynasties, the movement was mainly from east to west. The second period of the late Pleistocene saw an impulse in both directions, but mainly from west to east. The researchers also sequenced two new nuclear genomes from well-preserved horse fossils recovered from the Yukon Territory, Canada.
These were combined with 7 previously published nuclear genomes, allowing the team to measure the amount of gene flow between the Eurasian and North American populations. “The general opinion in the past was that horses differentiated into different species as early as they were in Asia, but these results suggest that there was continuity between populations,” said Dr. Ross McPhee said.
Journal Molecular Ecology
“They were able to interbreed independently, and we see results in fossil genomes on both sides of the split.” The new findings help redefine the question of why horses disappeared from North America, said Dr. Grant Zazula, a paleontologist for the Yukon government. “It was a regional population loss rather than an extinction.
We still don’t know why, but it tells us that conditions in North America at the end of the last ice age were dramatically different. If horses didn’t cross Asia, they would have been. lost everyone on the world stage. ” The results were published in the journal Molecular Ecology.