Ground Tit Genome Reveals Avian Adaptation to Living at High Altitudes in the Tibetan Plateau

Ground Tit Genome Reveals Avian Adaptation to Living at High Altitudes in the Tibetan Plateau

ARTICLE Received 21 Nov 2012 | Accepted 29 May 2013 | Published 1 Jul 2013 DOI: 10.1038/ncomms3071 Ground tit genome reveals avian adaptation to living at high altitudes in the Tibetan plateau Yanhua Qu1,*, Hongwei Zhao2,*, Naijian Han1, Guangyu Zhou2, Gang Song1, Bin Gao1, Shilin Tian2, Jinbo Zhang2, Ruiying Zhang1,5, Xuehong Meng2, Yuan Zhang2, Yong Zhang1, Xiaojia Zhu1,5, Wenjuan Wang1,5, David Lambert3, Per G. P. Ericson4, Sankar Subramanian3, Carol Yeung2, Hongmei Zhu2, Zhi Jiang2, Ruiqiang Li2,6 & Fumin Lei1 The ground tit (Parus humilis) is endemic to the Tibetan plateau. It is a member of family Paridae but it was long thought to be related to the ground jays because of their morpho- logical similarities. Here we present the ground tit’s genome and re-sequence two tits and one ground jay, to clarify this controversially taxonomic status and uncover its genetic adaptations to the Tibetan plateau. Our results show that ground tit groups with two tits and it diverges from them between 7.7 and 9.9 Mya. Compared with other avian genomes, ground tit shows expansion in genes linked to energy metabolism and contractions in genes involved in immune and olfactory perception. We also found positively selected and rapidly evolving genes in hypoxia response and skeletal development. These results indicated that ground tit evolves basic strategies and ‘tit-to-jay’ change for coping with the life in an extreme environment. 1 Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China. 2 Novogene Bioinformatics Institute, Beijing 100083, China. 3 Griffith School of Environment and School of Bimolecular and Physical Sciences, Griffith University, 170, Kessels Road, Nathan 4111, Australia. 4 Department of Vertebrate Zoology, Swedish Museum of Natural History, PO Box 50007, SE-10405 Stockholm, Sweden. 5 Graduate University of Chinese Academy of Sciences, Beijing 100081, China. 6 Peking-Tsinghua Center for Life Sciences, Biodynamic Optical Imaging Center (BIOPIC) and School of Life Sciences, Peking University, Beijing 100871, China. * These authors contributed equally to this work. Correspondence and requests for materials should be addressed to F.L. (email: [email protected]) or to R.L. (email: [email protected]). NATURE COMMUNICATIONS | 4:2071 | DOI: 10.1038/ncomms3071 | www.nature.com/naturecommunications 1 & 2013 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms3071 he Tibetan plateau is the largest high-altitude land mass on 38°0’0’’N the Earth, with an area of 2.3 million km2 and an average 1 Televation of 4,500 m above sea level . The collision of the Mongolian Indian subcontinent with the Eurasian plate during the Pliocene ground-jay 34°0’0’’N caused dramatic changes in the climate of the region, which Altitude became drier, colder and windier. Forests were replaced by Ground tit >5,000 grasslands, glaciers developed and deserts formed2. The cold climate in the Tibetan plateau and the resulting hypoxic 0 conditions created environments that are extremely hostile to 30°0’0’’N most organisms. These harsh conditions caused an unusually strong selection that drove speciation and led to the evolution of many animals that are now well-adapted to a life in the Tibetan 26°0’0’’N plateau3. To date we only have a limited understanding of the Great tit genetic background of these adaptations. One particularly interesting species endemic to the Tibetan Yellow- plateau is the ground tit (Parus humilis, Paridae), also known as 22°0’0’’N cheeked tit Hume’s ground tit and Tibetan ground tit. This is a drab coloured 96°0’0’’E 100°0’0’’E 104°0’0’’E 108°0’0’’E songbird that, unlike other tits, dwells exclusively above the tree Figure 1 | Sampling localities of three tits and the ground jay. The ground tit line (3,300–5,400 m) on rocky steppes and grasslands of the was collected in Gahai, Gansu province, China; the yellow-cheeked tit in Tibetan plateau4. Previous phylogenetic analysis suggest that the Longlin, Guangxi province, China; the great tit in Lijiang, Yunnan province, ground tit has evolved from an arboreal ancestor of the genus China; and Mongolian ground jay in Delingha, Qinghai province, China. Parus, the tits5. However, in contrast to its closest relatives, the ground tit has a longer and distinctly downward decurved bill, frequency method (Supplementary Table S2 and Supplementary longer legs, larger body size and paler overall plumage. It also Fig. S1). The contig and scaffold N50 sizes are 88.3 and exhibits behavioural traits that are different from those of 1615.4 kbp, respectively, with the largest scaffold spanning arboreal tits, as it forages on the ground and digs burrows or 6961.4 kbp and gap regions accounting for 0.85% of the whole tunnels for roosting and nesting6. In all these characters, the assembly (Supplementary Table S3). The genome assembly cov- ground tit closely resembles ground jays of the genus Podoces in ered 99.63% of the 11,453 high-quality unigenes assembled from the family Corvidae (crows, jays, magpies and their allies). 23.74 Gb RNA sequence data for lung and muscle tissues Indeed, the ground tit was long considered to be the smallest (Supplementary Tables S1–S4). Of unigenes that were covered by member of Corvidae and placed in a monotypic genus genome sequences, 89.19% exist in one intact scaffold, ensuring (Pseudopodoces). Given that both ground jays and ground tit that the assembly covered most of the transcriptional regions. The exclusively dwell in high steppes and adapt to living on the high overall coverage of 99.6% (Supplementary Fig. S2) and ground, their morphological similarities are likely to result from similarly comparable size and composition to other bird genomes convergent evolution7, for example, long decurved beaks for (Supplementary Table S5 and Supplementary Fig. S3) indicate probing the ground, elongated legs for hopping locomotion and that the assembly of the ground tit genome is characterized by a large body size for heat retention. The most severe environmental high level of accuracy. challenges to the ground tit in the Tibetan plateau are the hypoxic By genome-wide searching and homology prediction against the and low temperature. It can thus be hypothesized that this species Repbase database, we show that 9.09% of the ground tit genome has increased energy metabolism rates and elevated responses to belongs to the transposable element (TE) families (Supplementary hypoxic conditions, as have been shown for Tibetan native people Table S6). The overall repeat content, especially DNA transponsons and the yak8–10. (0.37%), long interspersed nuclear element (3.67%) and long To test this, we have generated and analysed the genome of the terminal repeats (3.03%), is similar to that of zebra finch (0.26%, ground tit and re-sequenced the genome of two closely related 3.40% and 3.55%, respectively), but differed from that of chicken tits, the great tit, Parus major and the yellow-cheeked tit, (0.97%, 6.29% and 1.49%) (Supplementary Table S7). There is a P. spilonotus, and the Mongolian ground jay, Podoces hendersoni. large proportion of highly divergent repeats compared with other Our results show that the ground tit exhibits elevated responses to avian genomes (Supplementary Fig. S4), suggesting considerable hypoxia and increased energy metabolism, the same survival ancient transposition with little recent activity. After masking the strategies that have been previously shown in other high-altitude repetitive regions, we annotated the genes using a combinational animals. Our study also suggests other adaptations in the ground method based on homology search, ab initio prediction, publicly tit to a life at high altitudes (for example, increased skeletal available EST/cDNA evidences and direct mRNA sequencing development, reduced feather keratins and olfactory genes). This evidences (Supplementary Table S8). This generated a total of genomic study provides insights into both genetic modifications 17,520 protein-coding genes and 830 other RNA genes that are crucial to a life in this extreme alpine environment, as (Supplementary Tables S9 and S10). Of the protein-coding genes, well as some unexpected genomic consequences resulting from 86.94% have homologues in the protein databases (including these adaptations. Swissprot and TrEMBL), and were classified into functional categories according to InterPro (ref. 11), KEGG (ref. 12) pathway data- base and Gene Ontology (GO) (ref. 13) (Supplementary Table S11). Results Genome assembly and annotation. We sequenced the genome of a female ground tit from Gahai, Gansu, China (Fig. 1) using a The ground tit is a real tit and not a jay. To further test the whole-genome shotgun strategy and the Illumina HiSeq 2000 phylogenetic position of the ground tit based on whole-genomic platform. De novo assembly of 1.85 billion reads from five paired- sequence, we re-sequenced one great tit, one yellow-cheeked tit end and mate-pair libraries provides 171-fold coverage with a and one Mongolian ground jay to B10-fold sequence coverage total assembly length of 1080.6 Mb (Supplementary Table S1), using Illumina technology, and aligned the data to the ground tit which approximates the genome size estimated using K-mer genome. The whole-genome alignment confirmed that the 2 NATURE COMMUNICATIONS | 4:2071 | DOI: 10.1038/ncomms3071 | www.nature.com/naturecommunications & 2013 Macmillan Publishers Limited. All rights reserved. NATURE COMMUNICATIONS | DOI: 10.1038/ncomms3071 ARTICLE Ground tit Great tit 100 6 Ground tit Great tit Ye l l ow - Mongolian 90 cheeked tit ground jay Ye l l ow - Mongolian 5 80 cheeked tit ground jay 70 4 60 50 3 40 2 30 Mismatch rate (%) Mismatch rate Reads mapping rate (%) Reads mapping rate 20 1 10 0 0 Ground tit Zebra finch Ground tit Zebra finch Aligned to the reference genome Aligned to the reference genome Ground tit 71 7.7 (4.8–11.9) 100 Yellow-cheeked tit 9.0 (5.9–13.5) 100 Great tit 33.2 (25.9–40.9) Mongolian ground jay 44.4 (39.9–49.9) Zebra finch 114.0 (101.7–120.6) Turkey 100 42.8 (39.7–49.2) Chicken Million years ago 100 80 60 40 20 0 Figure 2 | Phylogenetic relationship and distance of the ground tit.

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