Introgression of beneficial alleles has emerged as an important avenue for genetic adaptation in both plant and animal populations. In vertebrates, adaptation to hypoxic high-altitude environments involves the coordination of multiple molecular and cellular mechanisms, including selection on the hypoxia-inducible factor (HIF) pathway and the blood-O₂ transport protein hemoglobin (Hb). In two Andean duck species, a striking DNA sequence similarity reflecting identity by descent is present across the ~20 kb β-globin cluster including both embryonic (HBE) and adult (HBB) paralogs, though it was yet untested whether this is due to independent parallel evolution or adaptive introgression. In this study, we find that identical amino acid substitutions in the β-globin cluster that increase Hb-O₂ affinity have likely resulted from historical interbreeding between high-altitude populations of two different distantly-related species. We examined the direction of introgression and discovered that the species with a deeper mtDNA divergence that colonized high altitude earlier in history (Anas flavirostris) transferred adaptive genetic variation to the species with a shallower divergence (A. georgica) that likely colonized high altitude more recently possibly following a range shift into a novel environment. As a consequence, the species that received these β-globin variants through hybridization might have adapted to hypoxic conditions in the high-altitude environment more quickly through acquiring beneficial alleles from the standing, hybrid-origin variation, leading to faster evolution.

有益等位基因的渗入已成为植物和动物种群遗传适应的重要途径。在脊椎动物中，对缺氧高海拔环境的适应涉及多种分子和细胞机制的协调，包括对缺氧诱导因子（HIF）途径和血液-O ₂转运蛋白血红蛋白（Hb）的选择。在两个安第斯鸭物种中，在〜20 kb β-珠蛋白簇中存在惊人的DNA序列相似性，反映了血统同一性，包括胚胎（ HBE ）和成年（ HBB ）旁系同源物，尽管尚未测试这是否是由于独立所致平行进化或适应性渗入。在这项研究中，我们发现β-珠蛋白簇中增加Hb-O ₂亲和力的相同氨基酸取代可能是两个不同远缘物种的高海拔种群之间的历史杂交造成的。我们检查了基因渗入的方向，发现历史上早期在高海拔地区定居的具有较深线粒体DNA分歧的物种（黄嘴鸭）将适应性遗传变异转移到了最近在高海拔地区定居的具有较浅分歧的物种（格鲁吉亚雁）。可能是在范围转移到新环境之后。因此，通过杂交获得这些β-珠蛋白变体的物种可能通过从固定的杂交起源变异中获得有益的等位基因，更快地适应高海拔环境中的缺氧条件，从而导致更快的进化。