Three-generations low-altitude adaptations: Embryonic development, eggshell properties, and metabolic gene expression...

High-altitude hypoxia challenges avian embryonic development, prompting the evolution of phenotypic traits of plateau creatures such as the Snowy White chicken. However, how the possible changes in adaptations when those birds are transferred to lowland remain uncertain. We investigated the phenotypic and molecular changes over three generations (G0: the initial Generation in the plateau; G1 to G2: the first to second generation birds transferred to the lowland at Ya'an, Sichuan province) of Snowy White chickens. We assessed the eggshell characteristics at day 315 of the layers, and the organ index and the expression of hypoxia-responsive metabolic genes of heart, liver, lung, and kidney for the embryos at day 20 from G0 to G2. Our findings indicated that eggshell, as the most important structure affecting embryo respiration, exhibits significant changes. Birds from G1 and G2 exhibited increased eggshell thickness, reduced pore density, and decreased water vapor permeability compared with those in G0 (P < 0.05). The embryonic organ indices (heart, liver, lung and kidney) increased in G1 and G2 compared with those from G0 (P < 0.05). More interesting, G0 demonstrated higher levels of HIF-1α, VEGF, and glycolytic genes (GLUT2, HK2, and LDHA) in heart, lung, and kidney, but lower levels of oxidative phosphorylation genes (IDH2 and MDH1) (P < 0.05) than those by G1 and G2. Our findings of the low-altitude adaptations observed in Snowy White chickens indicate that the phenotypic and genetic expression pattern of important respiratory metabolism organs are reconfigurable to maintain the survival of the birds in the new environment. Our research offers valuable insights into the evolutionary dynamics of attitude adaption for those living being which tranters their living environment.