Origin and Evolution of Deleterious Mutations in Horses

Area of Science:

• Genomics
• Animal Breeding
• Evolutionary Biology

Background:

• Domestication has altered natural selection in horses, favoring specific traits and reducing genetic diversity.
• Reduced genetic diversity limits the removal of deleterious mutations, potentially increasing mutational load.
• Previous studies indicated a steady mutational load until a recent, rapid increase.

Purpose of the Study:

• To comprehensively characterize deleterious mutations in horses throughout domestication.
• To identify the factors contributing to the recent burst of deleterious mutations.
• To understand the impact of breeding practices on horse genomic health.

Main Methods:

• Analysis of an extensive dataset including 175 modern and 153 ancient horse genomes.
• Comprehensive characterization of deleterious mutations and their frequencies.
• Comparison of mutation loads across different historical periods and breeds.

Main Results:

• Deleterious variants remained at low frequencies for 3500 years.
• A significant increase in homozygous deleterious variants occurred in modern times.
• This increase was linked to inbreeding, closed studbooks, and breed endangerment, particularly in draft horses.
• The findings were consistent across multiple breeds.

Conclusions:

• Modern breeding practices, including inbreeding and breed conservation efforts, have paradoxically reduced the genomic fitness and viability of horses.
• The deprecation of horsepower led to population bottlenecks in draft breeds, exacerbating mutational load.
• Understanding these evolutionary impacts is crucial for future horse breeding and conservation strategies.