Are Chinese indigenous chicken breeds genetically “polluted” by commercial broilers?

Genomic study finds high levels of gene flow between Chinese indigenous chicken breeds and commercial broilers.

In total, 1714 out of 10 446 bird species (16.4%) have been documented to have hybridized with at least one other bird species in nature. When hybridization in captivity is included, this figure increases to 2204 species (21.1%).” These numbers are from my Ibis-paper where I quantified the incidence of hybridization in birds. Although this blog mainly focuses on avian hybrids in the wild, hybridization in captivity is quite common. In fact, interbreeding different species or varieties has been an important tool for animal breeders. The domestic chicken, for example, is probably the outcome of hybridization between several wild species.

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The domestic chicken is probably the outcome of hybridization between several wild species. ©Didactohedron | Wikimedia Commons

 

Double-edges Sword

Hybridization is a double-edged sword. On the one hand, it can introduce new genetic variation and drive adaptation. On the other hand, it can threaten the “genetic purity” of endangered species (see for example the case of the Milky Stork). Similar processes occur in captivity. For instance, interbreeding Large White pigs with Chinese pigs probably resulted in the exchange of the AHR haplotype which contributes to increased litter size, a desired trait in animal breeding practices. In Vietnam, however, mixing different pig breeds culminated in loss of genetic diversity of the Vietnamese Black H’mong pig breed. These examples show the complexities of hybridization in the context of animal breeding.

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Large White pigs have a larger litter size due to hybridization with Asian breeds (from: https://www.indiamart.com/)

 

Indigenous Chickens

A recent study in the journal Evolutionary Applications assessed the situation for Chinese indigenous chicken breeds. In China, these chickens constitute important genetic resources and are valued for several traits, such as early puberty, meat quality and resistance to certain diseases. However, they have a slower growth rate compared to commercial broilers. To increase the growth rate of these indigenous chickens, breeders have created several hybrid breeds, including Shiqi Za chicken, Three-Yellow chicken and Kuaida Silkie. These breeds are known to be admixed, but what about the original indigenous ones? Chunyuan Zhang (China Agricultural University) and her colleagues compared the genomes of several breeds to figure this out.

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A Silkie chicken breed (from: https://countrysidenetwork.com/).

 

High Levels of Introgression

The genetic analyses revealed high levels of introgression between indigenous chickens and commercial broilers. On average, about 15% of the genomes was of commercial origin. The highest percentage (21.5%) was found in the Huiyang Bearded chicken. These high percentages are probably due to the naive practices of local farmers that cross indigenous breeds with commercial ones. Although the impact of this widespread genetic exchange remains to be determined, the authors fear that it could “threaten current genetic resources and result in genetic pollution.”

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The Huiyang Bearded chicken breed (from: https://www.newscientist.com/)

 

References

Zhang, C., Lin, D., Wang, Y., Peng,. D., Li, H., Fei, J., Chen. K., Yang, N., Hu, X., Zhao, Y. & Li. N. (2019) Widespread introgression in Chinese indigenous chicken breeds from commercial broiler. Evolutionary Applications, 12(3): 610-621.

 

This paper has been added to the Galliformes page.

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