企鹅基因组研究
文章引用
Cai Li, Yong Zhang, Jianwen Li, Lesheng Kong, Haofu Hu, Hailin Pan, Luohao Xu, Yuan Deng, Qiye Li, Lijun Jin, Hao Yu, Yan Chen, Binghang Liu, Linfeng Yang, Shiping Liu, Yan Zhang, Yongshan Lang, Jinquan Xia, Weiming He, Qiong Shi, Sankar Subramanian, Craig D. Millar, Stephen Meader, Chris M. Rands, Matthew K. Fujita, Matthew J. Greenwold, Todd A. Castoe, David D. Pollock, Wanjun Gu, Kiwoong Nam, Hans Ellegren, Simon Y. W. Ho, David W. Burt, Chris P. Ponting, Erich D. Jarvis, M. Thomas P. Gilbert, Huanming Yang, Jian Wang, David M. Lambert, Jun Wang, and Guojie Zhang, 'Two Antarctic Penguin Genomes Reveal Insights into Their Evolutionary History and Molecular Changes Related to the Cold Antartic Environment', GigaScience (2014).
英文摘要
Background
Penguins are flightless aquatic birds widely distributed in the Southern Hemisphere. The distinctive morphological and physiological features of penguins allow them to live an aquatic life, and some of them have successfully adapted to the hostile environments in Antarctica. Two of them (Adélie penguin [Pygoscelis adeliae] and emperor penguin [Aptenodytes forsteri]) make the Antarctic continent as their major habitats. To study the phylogenetic and population history of penguins and the molecular basis of their adaptations to the Antarctica, we sequenced the genomes of the two Antarctic dwelling penguin species, Adélie and emperor penguins.
Results
Phylogenetic dating suggests that early penguins arose ~60 million years ago (MYA), coinciding with a period of global warming. Analysis of effective population sizes reveals that the two penguin species experienced population expansions from ~1 MYA to ~100 KYA, but responded differently to the climate cooling of the last glacial period. Comparative genomic analyses with other available avian genomes identified molecular changes in genes related to epidermal structure, phototransduction, lipid metabolism, and forelimb morphology.
Conclusions
Our sequencing and initial analyses of the first two penguin genomes provide insights into the timing of penguin origin, the fluctuations of effective population sizes of the two penguin species over the past 10 million years, and the potential associations between these biological patterns and global climate change. The molecular changes compared to other avian genomes reflect both shared and diverse adaptations of the two penguin species to the Antarctic environment.
文章解读
“身残志坚”的企鹅
企鹅外表呆萌可爱，是家喻户晓的“明星”。然而，一般明星的背后都有着不少特殊的故事。其实，企鹅在鸟类家族中可以说是特立独行的一类，跟其它很多鸟类不一样，企鹅不能在天空自由翱翔，发福的身材走起路来都不太方便，翅膀和羽毛虽然退化，光滑的身躯却使得其可以在水中自由驰骋。此外不少企鹅生活在南极，成为南极生态圈里最为活跃的一类生物。
企鹅的独特形态和令人惊叹的生活史（可参考纪录片《帝企鹅日记》）吸引了众多科学家对它们进行研究。最近，科学家首次对两种生活在南极大陆的企鹅（帝企鹅和阿德利企鹅）进行了全基因组测序，从基因组水平进一步窥探企鹅作为“明星”背后的秘密。
鸟落南洋戏水去
研究的第一步是需要确认企鹅在鸟类家谱中的位置，研究人员利用企鹅和其它鸟类的基因组构建了全新的物种演化树。研究发现，在这个家谱中离企鹅最近的是鹱形目的鸟类，鹱形目中有人们熟悉的信天翁和海燕。说明企鹅跟鹱形目的祖先都是海鸟，大约在6000万年前，企鹅跟鹱形目各自形成。据猜测，由于当时全球气候变暖，使得企鹅的祖先可以飞到南半球纬度更高的海域，最终到了南极并适应了那里的生活。
娇躯渐胖终不悔
企鹅体态丰腴，有着肥硕的水桶腰，这种事情发生在人类身上也许会被认为长“残”了，但这却是企鹅傲人的资本，因为这些厚厚的脂肪可以帮助它们抵御南极的极寒。在企鹅基因组中发现，有多个与脂肪代谢相关的基因受到了自然选择。这些基因影响着脂肪在企鹅体内的合成、代谢以及贮藏。企鹅在演化过程中由于御寒的需要，不断改变脂肪的代谢与贮藏等方式，将自己的小蛮腰变成了水桶腰，从而有效地战胜了南极的极寒。
残肢破浪会有时
在演化过程中，企鹅翅膀的变化非常明显，之前的长翅膀演化成了短翅膀。这种类似鱼鳍的短翅膀非常有利于企鹅在水中游泳和捕食。研究发现，多个与前肢发育相关基因在企鹅中发生了特异性的突变，这些变异很可能影响其编码蛋白的功能。其中两个发生突变的基因EVC和EVC2，在人类当中发生突变后会导致四肢短小，轴后多指畸形等症状，与企鹅的前肢形态有相似之处。科学家猜测，这些基因的突变使得企鹅演化出了适合游泳的小短肢，虽然这种短小的前肢看似“残疾”，却有利于它们在水下捕食，从而帮助企鹅们笑傲南极。