Genetic Diversity and Selection Patterns in Icelandic and Exmoor Horses

Jenn Hoskins
9th August, 2024

Genetic Diversity and Selection Patterns in Icelandic and Exmoor Horses

Image Source: 光曦 刘 (photographer)

Key Findings

  • The study compared genetic diversity and inbreeding in Icelandic horses and Exmoor ponies, revealing significant differences due to their distinct selection pressures
  • Both breeds showed significant runs of homozygosity (ROH), but the Icelandic horse had ROH concentrated in specific regions, indicating targeted selection for traits like gait performance
  • The Exmoor pony exhibited a more even distribution of ROH, reflecting its focus on conservation and maintaining breed standards rather than specific trait selection
The study of genetic diversity in animal populations is crucial for understanding their evolutionary history and ensuring their future viability. The Swedish University of Agricultural Sciences recently conducted a study to assess genetic diversity in two ancient horse breeds, the Icelandic horse and the Exmoor pony[1]. Both breeds have adapted to harsh environmental conditions and have experienced severe historical population bottlenecks. However, modern selection pressures on these breeds differ significantly. This study aimed to compare their genetic diversity, inbreeding levels, and signatures of selection. The researchers evaluated genetic diversity using two key metrics: expected heterozygosity (HE) and observed heterozygosity (HO). Heterozygosity measures the genetic variation within a population, with higher values indicating greater diversity. Additionally, the study estimated the effective population size (Ne), which reflects the number of individuals contributing genes to the next generation. A smaller Ne can lead to increased inbreeding and reduced genetic diversity, posing a risk to the population's health and adaptability. One of the study's primary focuses was on runs of homozygosity (ROH). ROH are continuous stretches of homozygous genotypes in an individual's genome, indicating regions where both copies of the gene are identical. These regions can provide insights into a population's inbreeding levels and past demographic events[2]. By identifying and characterizing ROH, the researchers aimed to estimate genomic inbreeding and detect signatures of selection in the Icelandic horse and Exmoor pony. The study found that both breeds exhibited significant ROH, consistent with their history of population bottlenecks. However, the distribution and length of these ROH varied between the breeds, reflecting their different selection pressures in modern times. For example, the Exmoor pony, which has not been subjected to intense selection for specific traits, showed a more even distribution of ROH across its genome. In contrast, the Icelandic horse displayed ROH concentrated in specific genomic regions, suggesting targeted selection for particular traits. These findings align with previous studies on other horse breeds. For instance, a study on Swedish Warmblood horses identified long ROH in regions associated with behavior, physical abilities, and fertility, which are likely targets of selection for equestrian sport performance[3]. Similarly, research on German warmblood breeds revealed selection signals in genes affecting muscle functionality, energy metabolism, and fertility, indicating that breeding programs have shaped these genomes to enhance specific traits[4]. By comparing the Icelandic horse and Exmoor pony, the Swedish University of Agricultural Sciences study provides valuable insights into how different selection pressures can influence genetic diversity and inbreeding levels in animal populations. The results highlight the importance of considering both historical and modern factors when managing and conserving genetic resources in livestock breeds. In conclusion, the study underscores the utility of ROH in understanding genetic diversity and inbreeding in animal populations. By revealing how selection pressures shape genomic architecture, such research can inform breeding programs and conservation strategies aimed at maintaining genetic health and adaptability in endangered breeds.

GeneticsAnimal ScienceEvolution

References

Main Study

1) Genetic diversity and signatures of selection in Icelandic horses and Exmoor ponies

Published 8th August, 2024

https://doi.org/10.1186/s12864-024-10682-8

Related Studies

2) Runs of homozygosity: current knowledge and applications in livestock.

https://doi.org/10.1111/age.12526

3) Signatures of selection in the genome of Swedish warmblood horses selected for sport performance.

https://doi.org/10.1186/s12864-019-6079-1

4) Selection signatures in four German warmblood horse breeds: Tracing breeding history in the modern sport horse.

https://doi.org/10.1371/journal.pone.0215913


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