Data from: Stepwise colonization of the Andes by Ruddy Ducks and the evolution of novel β-globin variants

Andean uplift played a key role in Neotropical bird diversification, yet past dispersal and genetic adaptation to high-altitude environments remain little understood. Here we use multilocus population genetics to study population history and historical demographic processes in the ruddy duck (Oxyura jamaicensis), a stiff-tailed diving duck comprising three subspecies distributed from Canada to Tierra del Fuego and inhabiting wetlands from sea level to 4500 m in the Andes. We sequenced the mitochondrial DNA, four autosomal introns and three haemoglobin genes (αA, αD, βA) and used isolation-with-migration (IM) models to study gene flow between North America and South America, and between the tropical and southern Andes. Our analyses indicated that ruddy ducks dispersed first from North America to the tropical Andes, then from the tropical Andes to the southern Andes. While no nonsynonymous substitutions were found in either α globin gene, three amino acid substitutions were observed in the βA globin. Based on phylogenetic reconstruction and power analysis, the first βA substitution, found in all Andean individuals, was acquired when ruddy ducks dispersed from low altitude in North America to high altitude in the tropical Andes, whereas the two additional substitutions occurred more recently, when ruddy ducks dispersed from high altitude in the tropical Andes to low altitude in the southern Andes. This stepwise colonization pattern accompanied by polarized βA globin amino acid replacements suggest that ruddy ducks first acclimatized or adapted to the Andean highlands and then again to the lowlands. In addition, ruddy ducks colonized the Andean highlands via a less common route as compared to other waterbird species that colonized the Andes northwards from the southern cone of South America.

安第斯造山运动（Andean uplift）在新热带区鸟类的多样化进程中扮演了关键角色，但学界对于新热带区鸟类过往的扩散事件以及对高海拔环境的遗传适应机制仍知之甚少。本研究采用多位点种群遗传学方法，对棕硬尾鸭（Oxyura jamaicensis）的种群历史与历史种群动态过程展开探究。棕硬尾鸭是一类硬尾潜水鸭，共包含3个亚种，分布范围从加拿大延伸至火地岛，栖息于从海平面至安第斯山脉4500米海拔的各类湿地中。我们对线粒体DNA、4个常染色体内含子以及3个血红蛋白基因（αA、αD、βA）进行了测序，并借助隔离与迁移（isolation-with-migration, IM）模型，分析了北美与南美之间、热带安第斯与南部安第斯之间的基因流情况。分析结果表明，棕硬尾鸭的扩散路径为先从北美迁至热带安第斯，随后再从热带安第斯迁至南部安第斯。尽管在两类α球蛋白基因中均未发现非同义替换，但在βA球蛋白基因中观测到3处氨基酸替换。基于系统发育重建与效力分析，在所有安第斯种群个体中均存在的首个βA替换，是在棕硬尾鸭从北美低海拔区域扩散至热带安第斯高海拔区域时获得的；而另外两处替换则发生在更近的时期，对应棕硬尾鸭从热带安第斯高海拔区域扩散至南部安第斯低海拔区域的过程。这种伴随定向βA球蛋白氨基酸替换的分步定殖模式表明，棕硬尾鸭先是逐步适应了安第斯高原的高海拔环境，随后又再次适应了南部安第斯的低海拔环境。此外，相较于其他从南美南锥体向北扩散至安第斯山脉的水鸟物种，棕硬尾鸭完成安第斯高海拔区域定殖所采用的路径更为罕见。