Indigenous chickens in tropical regions routinely survive high environmental temperatures (40-45 °C) that cause significant mortality and production loss in commercial breeds, yet the genetic mechanis Show more
Indigenous chickens in tropical regions routinely survive high environmental temperatures (40-45 °C) that cause significant mortality and production loss in commercial breeds, yet the genetic mechanisms of thermotolerance remain poorly understood. This study integrated genome-wide selective scans across 14 geographically and climatically diverse chicken breeds with multi-tissue expression data, gene expression quantitative trait locus (eQTL) analysis, transcriptome-wide association study (TWAS), and cross-species phenome-wide association study (PheWAS) to validate candidate genes. We identified 25 high-confidence genes under selection, with ATP1A1, PLCB4, RYR2 and AKT3 forming a regulatory hub coordinating cardiovascular, calcium and survival signaling. These genes converge on interconnected adrenergic, calcium, and GnRH signaling pathways, with coordinated expression across heart, hypothalamus, and liver forming an integrated thermoregulatory axis. The eQTL integration analysis using ChickenGTEx data identified 359 tissue-specific cis-eQTLs in selected regions. Additionally, TWAS analysis linked ATP1A1 to 145 gene-trait associations across 13 tissues and 14 trait categories (hepatic regulation, β = -2.13, p = 4.21 × 10⁻¹²), and cross-species PheWAS validated conserved roles in cardiovascular function (RYR2, resting heart rate p = 4.9 × 10⁻¹²), and ionic homeostasis (ATP1A1, chloride p = 1.18 × 10⁻³). In parallel, we also identified robust genomic signatures of domestication in classic candidate genes (TSHR, TBC1D1, BDNF), highlighting how initial separation from Red Jungle Fowl and subsequent adaptation to diverse climates have shaped the genetic and physiological diversity of the domesticated chicken. Collectively, our results reveal an integrated cardio-neuroendocrine calcium network driving heat adaptation, providing potential targets for breeding heat-tolerant chickens. Show less