Extinct Dalian horse as a genetic bridge between Late Pleistocene North American and Eurasian equids.

Overview

• This study investigates the extinct Dalian horse from northeastern China, revealing its unique genetic identity and its role as a genetic bridge linking Late Pleistocene horses from North America and Eurasia.
• The research shows how this horse species contributed to the genetic connectivity of ancient horse populations across a broad geographic range and provides insights into its extinction.

Background and Significance

• During the Late Pleistocene epoch, caballine horses (horse species closely related to modern horses) displayed significant genetic diversity and wide-ranging population connectivity across North America and Eurasia.
• The Dalian horse (Equus dalianensis), now extinct, was native to northeastern China and hypothesized to be part of this interconnected genetic network.
• Understanding the Dalian horse’s genetic makeup helps clarify the patterns of gene flow and population dynamics among ancient horse species across continents.

Research Methods

• Scientists sequenced 20 complete mitochondrial genomes and two nuclear genomes from Dalian horse remains.
• They compared these genetic sequences with those of other Late Pleistocene horses from Northeast Asia and North America.
• Ancestry component analyses were performed to detect the presence and proportion of genetic influences from Eastern Beringian (E-EBer) populations—those from American regions near the Bering Strait.
• Stable isotope data were integrated to understand the ecological and dietary habits of the Dalian horse.

Key Findings

• The Dalian horse is genetically distinct and forms its own clade within Northeast Eurasian caballine horses, suggesting it was a separate lineage within this region.
• Its geographic distribution is broader than previously known, extending across northeastern Asia.
• Genetic evidence shows the Dalian horse carried a significant proportion of Eastern Beringian (American) ancestry, which is unique among Northeast Asian horses.
• This proportion of American ancestry ranged between approximately 50,000 to 32,000 years ago, indicating periods of contact and gene flow, followed by genetic dilution through later mixing with other populations.
• Late Pleistocene Northeast Siberian horses show much lower (<0.7%) and uneven E-EBer ancestry, pointing to limited gene flow compared to the Dalian horse.
• The overlap and admixture patterns between Dalian and Northeast Siberian horses support the idea that Dalian horses acted as intermediaries, facilitating the transfer of American ancestry into Eurasian horse populations.

Ecological and Extinction Insights

• Stable isotope data suggest the Dalian horse had a specialized dietary niche, likely restricting it to certain types of forage or habitats.
• This specialized diet and ecological niche may have limited the horse’s ability to adapt to rapid environmental changes occurring during the Late Pleistocene.
• These environmental pressures and limited adaptability contributed to the eventual extinction of the species.

Implications and Conclusions

• The study provides a clearer understanding of the genetic landscape and population connectivity of horses in northern Asia during the Late Pleistocene.
• The Dalian horse played an important role as a genetic bridge, transferring genetic material from North American horse populations to Eurasian groups.
• These dynamics emphasize the complexity of horse evolutionary history and the influence of environmental change on their survival and extinction.
• The research enhances knowledge about past biodiversity patterns, evolutionary processes, and extinction mechanisms in prehistoric ecosystems.