Researchers delve into the maternal DNA of Italian horse breeds

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stock-eyes_1764The ancestral local mares that gave rise to Italy’s horse breeds must have harbored an extensive genetic diversity, researchers report.

The climatic and cultural diversity of the Italian Peninsula triggered, over time, the development of a wide variety of horse breeds. Light horses are typical of the drier central and southern regions, while the northern wet regions are characterized by heavy horses.

The origin and history of the breeds are still unclear.

To clarify this issue, researchers have been analysing traits and studying genealogical data, and have even used molecular screening to learn more about their origins.

The researchers, from the University of Perugia and other tertiary institutions, set out to obtain a comprehensive overview of the breeds’ genetic variability by studying mitochondrial DNA. This DNA, in the mitochondria of cells, is passed only down the female line.

Alessandro Achilli and his colleagues analysed 407 mitochondrial DNA control-region sequences from 10 of the most important Italian riding horse and pony breeds – Bardigiano, Esperia, Giara, Lipizzaner, Maremmano, Monterufolino, Murgese, Sarcidano, Sardinian Anglo-Arab, and Tolfetano. These breeds are a mix of Italian hotblood and warmblood horses, and pony breeds.

They also checked samples from 36 Arabian horses to assess the genetic consequences of their common use for the improvement of some local breeds.

In Italian horses, all previously described domestic mitochondrial DNA haplogroups were detected, as well as a high haplotype diversity, the researchers reported in the open-access journal, PLOS ONE. A haplotype is a set of DNA variations that tend to be inherited together.

“These findings indicate that the ancestral local mares harbored an extensive genetic diversity.”

They said that limited haplotype sharing (11%) with the Arabian horse indicated that its impact on the autochthonous mitochondrial gene pools during the final establishment of pure breeds was marginal, if any.

“The only significant signs of genetic structure and differentiation were detected in the geographically most isolated contexts (that is, Monterufolino and Sardinian breeds).

“Such a geographic effect was also confirmed in a wider breed setting, where the Italian pool stands in an intermediate position together with most of the other Mediterranean stocks.

“However, some notable exceptions and peculiar genetic proximities lend genetic support to historical theories about the origin of specific Italian breeds.”

They said it was worth noting that Italian breeds show a frequency of haplogroup L (23.9%) which is intermediate between those recorded in Western Asia (18.1%) and in Continental Europe (31.1%).

An additional clue to the likely east-west direction of the gene flow is found in the overall haplogroup frequencies of Italian horses, which are more similar to the breeds from Southwest Asia than those from Continental Europe.

“These findings probably reflect the overall mitochondrial DNA legacy of the ancestral mares (of eastern origins) that a long time ago were probably used at the initial stages of breeding selections.

“Those mitochondrial lineages were also preserved during the final establishment of pure breeds that was mainly reached through sex-biased breeding practices, which often involved the intensive use of few selected external stallions.

“Thus, the impact on the original mitochondrial DNA gene pool could have been marginal, as also testified by the only four haplotypes shared between the Arabian horses and the 10 Italian breeds here analyzed in spite of the well-recognized use of the Arabian stallions to revitalize some Italian breeds.”

Cardinali I, Lancioni H, Giontella A, Capodiferro MR, Capomaccio S, Buttazzoni L, et al. (2016) An Overview of Ten Italian Horse Breeds through Mitochondrial DNA. PLoS ONE 11(4): e0153004. doi:10.1371/journal.pone.0153004

The full study, published under a Creative Commons License, can be read here

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