飞行是鸟类区别于其他脊椎动物最显著的特征之一，需要在神经系统的控制下，由肌 肉、骨骼和羽片所构成的飞行器官协同完成。这一特性有利于鸟类完成觅食、迀徙、繁殖、 躲避天敌等生命活动。然而有少数现生鸟类如鸵鸟、几维鸟等却丧失了这一特性。一些学 者尝试利用系统发育关系或线粒体基因组揭开导致这一现象出现的原因，现已理清了部分 飞行退化鸟类的亲缘关系并就飞行进化问题作出了一些推测，使该领域的研宄工作获得推 进。但有关飞行退化的遗传学机制研宄却鲜有报道，全基因组水平上的机理研宄更是属于 空白。随着第二代测序技术的快速发展，越来越多的鸟类基因组数据得以发布。因此，本 研宄旨在全基因组水平上，对飞行鸟类和飞行退化鸟类的基因组数据进行比较分析，探讨 鸟类飞行退化的遗传学机制。 本研宄采用筛选祖先位点的趋同进化分析方法，通过对飞行组鸟类和飞行退化组鸟类 的3415个直系同源基因的祖先位点重构和筛选，共获得130个趋同进化位点，涉及120 个趋同进化基因。研宄结果证实了飞行退化组鸟类的确存在趋同进化现象。对120个趋同 进化基因的功能富集分析结果显示：与能量代谢有关的通路（ko00010: Glycolysis / Gluconeogenesis; ko04975: Fat digestion and absorption)和结构域（G0:0006629Lipid metabolic process)的富集最显著，由此可以得出飞行退化与能量代谢之间存在有非常重要 的联系。 进一步对这些与能量代谢相关的通路和结构域进行研宄发现，水解甘油三酯的关键性 脂肪酶(adipose triglyceride lipase，ATGL或PNPLA2、的特定SNP位点呈现出非常显著的趋 同进化信号，在飞行鸟类的碱基型为A，飞行退化鸟类为G。该碱基变化引起了编码过程 中的非同义突变，在飞行鸟类中编码丝氨酸，而在飞行退化组则编码甘氨酸。该非同义突 变位点恰好落在ATGL的酶活性调控区，很可能影响该脂肪酶的活性。在NCBI现有的58 个鸟类数据中进一步检测该位点，趋同现象仍旧成立。同时，这也为趋同进化新方法的可 靠性提供了一个强有力的证据。 脂肪酶水解脂肪可为鸟类飞行提供大量能量。而飞行能力弱化鸟类相对飞行鸟类而言， 机动性和活动范围都不及前者，整体的能量消耗相对较少，因此本研宄就飞行退化的遗传 学机制提出如下假说：飞行能力退化的鸟类脂肪酶ATGL特异的氨基酸的替代导致水解脂 肪酶的活性降低，水解脂肪的能力减弱，提供能量减少，成为鸟类飞行退化的根本原因。 关键词：

Flight is the most remarkable feature distinguishing birds from all other vertebrates. This behavior is innervated and executed through the flight organs comprising the light bones, strength muscle and pinnae. For birds, this feature is beneficial for hunting, surviving, reproduction and predator avoidance. However, the flight ability is degenerated in manyavian species. To date, the molecular mechanism underlying this process remains unknown. Thanks to the next generation sequencing technology, the genome sequences of a large number of bird species are available. To gain insight into the genetic basis for the degeneration of flight, we identified and analyzed the convergent signal of the flightless birds (N = 8) by comparing them with those with strong flight ability (N = 16). We totally identified 130 convergent sites involved 120 genes by reconstructing the ancestor statement using PAML for the 3,415 orthologous genes present in the 24 selected birds, indicating the presence of convergent evolution among these flight degenerated avian species.Surprisingly, the convergent genes were significantly enriched for pathways (KEGG pathway: ko00010: Glycolysis / Gluconeogenesis; ko04975: Fat digestion and absorption) and categories (GO:0006629, Lipid metabolic process) related to energy metabolism. Remarkably, one SNP showing strong convergent signal (GversusA) is located in theadipose triglyceride lipasegene (ATGL or PNPLA2), which is a patatin-like phospholipase domain-containing enzyme thathydrolyzes fatty acids from triacylglycerol (TAG) stored in multiple tissues. The nucleotide substitution in this site leads to a non-synonymous amino acid changes from Serine in flight birds to Glycine in flightless birds, which is exactly located in the lipid-bindingdomain. We further confirmed this observation by manually checking 58 avian species available in NCBI. With such solid results, it also proved the reliability and power of the new convergent method implemented. ATGL could hydrolyze fat to generate largequantity of energy. The energy is more important for flight bird than flightlessones because oftheir powerful movement, that is, the flight birds need more energy than flight degeneration birds in general. We therefore hypothesized that the amino acid change decreases the enzyme activity of ATGL in flightless birds, resulting in low efficiency of fat acid transformation in them. The decreased efficiency of energy supply provides an answer for the degeneration of flight in some bird species.