Research Note: Possible influence of thermal selection on patterns of HSP70 and HSP90 gene polymorphisms in Thai indigenous and local chicken breeds and red junglefowls.

ABSTRACT

The thermal stress caused by global climate change adversely affects the welfare, productivity, and reproductive performance of farm animals, including chickens, and causes substantial economic losses. However, the understanding of the genetic basis of the indigenous chicken adaptation to high ambient temperatures is limited. Hence, to reveal the genetic basis of thermal stress adaptation in chickens, this study investigated polymorphisms in the heat shock protein 70 (HSP70) and HSP90 genes, known mechanisms of cellular defense against thermal stress in indigenous and local chicken breeds and red junglefowls in Thailand. The result revealed seven alleles of the HSP70 gene. One allele exhibited a missense mutation, where an amino acid changed from Asn to His in the substrate-binding and peptide-binding domains, which is exclusive to the Lao Pa Koi chicken breed. Twenty new alleles with silent mutations in the HSP90 gene highlighted its greater complexity. Despite this diversity, distinct population structures were not found for either HSP70 or HSP90, which suggests incomplete impact on the domestication process and selection. The low genetic diversity, shown by the sharing of alleles between red junglefowls and Thai indigenous and local chicken breeds, aligns with the hypothesis that these alleles have undergone selection in tropical regions, such as Thailand. Selection signature analysis suggests the purifying selection of HSP70 for thermotolerance. This study provides valuable insights for enhancing the conservation of genetic resources with thermotolerant traits, which are essential for developing breeding programs to increase poultry production in the context of global climate change.