A genetic signature of the evolution of loss of flight in the Galapagos cormorant

We have a limited understanding of the genetic and molecular basis of evolutionary changes in the size and proportion of limbs. We studied wing and pectoral skeleton reduction leading to flightlessness in the Galapagos cormorant (Phalacrocorax harrisi). We sequenced and de novo assembled the genomes of four cormorant species and applied a predictive and comparative genomics approach to find candidate variants that may have contributed to the evolution of flightlessness. These analyses and cross-species experiments in Caenorhabditis elegans and in chondrogenic cell lines implicated variants in genes necessary for transcriptional regulation and function of the primary cilium. Cilia are essential for Hedgehog signaling, and humans affected by skeletal ciliopathies suffer from premature bone growth arrest, mirroring skeletal features associated with loss of flight.

目前学界对肢体大小与比例演化改变的遗传和分子基础认知仍较为有限。本研究以加拉帕戈斯鸬鹚（Phalacrocorax harrisi）为研究对象，探究其翼部与胸骨骼退化、最终丧失飞行能力的演化机制。我们对4种鸬鹚的基因组进行了测序与从头组装（de novo assembly），并采用预测性比较基因组学方法，筛选出可能与飞行能力丧失演化相关的候选变异位点。通过上述分析以及在秀丽隐杆线虫（Caenorhabditis elegans）与软骨生成细胞系中开展的跨物种实验，我们发现这些候选变异位点与负责初级纤毛功能及转录调控的相关基因存在关联。纤毛是Hedgehog信号通路（Hedgehog signaling）发挥正常功能的必需结构；罹患骨骼纤毛病的人类会出现骨骼生长过早停滞的症状，这与飞行能力丧失相关的骨骼特征高度吻合。