Genetic diversity and population structure in Brazilian Mangalarga Marchador horses.

The research explores the genetic diversity and population structure of Mangalarga Marchador horses in three distinct regions of Minas Gerais State, Brazil. Results suggest that despite relatively little geographical structure, there’s significant genetic structure within the population, leading to recommendations for breeding strategies.

Methodology

• The study used 115 unrelated Mangalarga Marchador horses from South, Southeast, and Northeast regions of Minas Gerais State, Brazil. Microsatellite loci, sections of DNA, were extracted and tested from these horses. These areas of DNA are crucial for understanding genetic variation and heredity.
• 10 microsatellite loci were tested using a variety of software packages. These are valuable in population genetics for determining diversity and structure.
• Under Hardy-Weinberg’s genetic equilibrium model, seven markers were at equilibrium, meaning the proportions of alleles remain constant over generations. This suggests no evolutionary changes (i.e., no mutation, migration, selection, or random genetic drift). Yet, two markers showed significant homozygote excess, indicating low genetic variation.

Findings

• In the nine microsatellite markers, 74 alleles were identified with an average of 8.22 alleles. The average heterozygosity was 0.637, indicating high genetic diversity, while the polymorphism information content (level of genetic variation) was 0.662.
• Five microsatellite markers were deemed highly informative (with a PIC >0.7). These can be useful for expanding tests to determine parentage.
• Geographical structure was deemed relatively insignificant, with an F(ST) value of 0.0562. This value measures the degree of genetic differentiation among subpopulations – the smaller the number, the more similar the populations are.
• A Bayesian-based cluster analysis allocated 94% of the tested horses accurately to their sampled subpopulations, suggesting that the population is genetically structured.
• The average pairwise f value, a measure of inbreeding or genetic similarity, was relatively high at 0.11, implying some level of relatedness among the sampled individuals.
• Despite attempts to avoid closely related individuals, 1% of individual pairs shared over 50% of alleles, suggesting a certain degree of inbreeding.

Conclusion and Recommendations

• The results provide strong evidence of genetic structuring within the Mangalarga Marchador horses population in Brazil.
• The study suggests two main strategies for preserving the genetic diversity of the population: preventing breeding between highly inbred individuals and encouraging breeding between horses from regions with low identified genetic flow.