title: Comparative transcriptomic analysis revealed adaptation mechanism of Phrynocephalus erythrurus, the highest altitude Lizard living in the Qinghai-Tibet Plateau.
abstract: BACKGROUND
  Organisms living at high altitudes must overcome three major environmental challenges: hypoxia, cold, and intense UV radiation. The molecular mechanisms that enable these challenges to be overcome have mainly been studied in endothermic organisms; relatively little attention has been paid to poikilothermic species. Here, we present deep transcriptome sequencing in two closely related lizards, the high altitude-dwelling Phrynocephalus erythrurus and the lowland-dwelling P. putjatia, to identify candidate genes under positive selection and to explore the convergent evolutionary adaptation of poikilothermic animals to high altitude life.
  
  
  RESULTS
  More than 70 million sequence reads were generated for each species via Illumina sequencing. De novo assembly produced 56,845 and 63,140 transcripts for P. erythrurus and P. putjatia, respectively. P. erythrurus had higher Ka/Ks ratios than P. putjatia, implying an accelerated evolutionary rate in the high altitude lizard lineage. 206 gene ontology (GO) categories with accelerated evolutionary rates and 43 candidate positively selected genes were detected along the P. erythrurus lineage. Some of these GO categories have functions associated with responses to hypoxia, energy metabolism and responses to UV damage. We also found that the high-altitude ranid frog R. kukunoris had higher Ka/Ks ratios than the closely related low-altitude frog R. chensinensis, and that the functional categories with accelerated evolutionary rates in R. kukunoris overlapped extensively with those detected along the P. erythrurus lineage.
  
  
  CONCLUSIONS
  The mechanisms of high altitude adaptation in P. erythrurus were tentatively inferred. By comparing two pairs of low- and high-altitude poikilothermic species, we found that similar functional categories had undergone positive selection in high altitude-dwelling Phrynocephalus and Rana lineages, indicating that similar mechanisms of adaptation to high altitude might have evolved in both genera. Our findings provide important guidance for future functional studies on high altitude adaptation in poikilothermic animals.
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. yangyongzhi2008@gmail.com.
authors.forename: Yongzhi
authors.initials: Y
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. wanglizhong.lzu@gmail.com.
authors.forename: Lizhong
authors.initials: L
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. hanjin@lzu.edu.cn.
authors.forename: Jin
authors.initials: J
authors.lastname: Han
authors.affiliation: Institute of Biochemistry and Molecular Biology, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. tangxl@lzu.edu.cn.
authors.forename: Xiaolong
authors.initials: X
authors.lastname: Tang
authors.affiliation: Institute of Biochemistry and Molecular Biology, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. mma@lzu.edu.cn.
authors.forename: Ming
authors.initials: M
authors.lastname: Ma
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. wk8910@gmail.com.
authors.forename: Kun
authors.initials: K
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. zhangxiao14@lzu.edu.cn.
authors.forename: Xiao
authors.initials: X
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. 778315181@qq.com.
authors.forename: Qian
authors.initials: Q
authors.lastname: Ren
authors.affiliation: Institute of Biochemistry and Molecular Biology, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. chenq@lzu.edu.cn.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Grassland Agro-ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, China. qiuqiang@lzu.edu.cn.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Qiu
mesh_terms: D000222:Adaptation, Physiological; D000531:Altitude; D000818:Animals; D008116:Lizards / Q000235:genetics* / Q000502:physiology; D010100:Oxygen / Q000378:metabolism; D010802:Phylogeny; D012641:Selection, Genetic; D017423:Sequence Analysis, RNA; D018609:Tibet; D059467:Transcriptome
chemical_list: D010100:Oxygen