The highs and lows of bird flight

Chromosome-level genome assembly of the bar-headed goose (Anser indicus)

Bar-headed geese (Anser indicus) are adaptable to plateau environments. In this study, we sequenced and assembled a high-quality chromosome-level genome of the bar-headed goose using PacBio long reads and Hi-C technique, and generated 115.73 Gb of Illumina short-reads and 95.89 Gb of PacBio long-reads. The assembled bar-headed goose genome, with a contig N50 of 5.734 Mb and a scaffold N50 of 65.77 Mb, is 1.129 Gb in length and includes 33 chromosomes and 451 fragments. BUSCO assessment yielded a completeness score of 94.4%. In total, 15,376 protein-coding genes were predicted, of which 94.95% had homologs in protein databases. We identified 78 positively selected genes (PSGs) in the bar-headed goose genome, which were mainly enriched in calcium ion and ATP-binding. This bar-headed goose genome will be an important resource for increasing our understanding regarding the genetic basis of adaptation to life at a high altitude.

Coping with extremes: High-altitude sparrows enhance metabolic and thermogenic capacities in the pectoralis muscle and suppress in the liver relative to their lowland counterparts

Animals living at high altitudes are challenged by the extreme environmental conditions of cold temperature and hypobaric hypoxia. It is not well understood how high-altitude birds enhance the capacity of metabolic thermogenesis and allocate metabolic capacity in different organs to maximize survival in extreme conditions of a cold winter. The Qinghai-Tibet Plateau (QTP) is the largest and highest plateau globally, offering a natural laboratory for investigating coping mechanisms of organisms inhabiting extreme environments. To understand the adaptive strategies in the morphology and physiology of small songbirds on the QTP, we compared plasma triiodothyronine (T₃), pectoralis muscle mitochondrial cytochrome c oxidase (COX) and state IV capacities, the expression of peroxisome proliferator-activated receptor γ coactivator α (PGC-1α), adenine nucleotide translocase (ANT), uncoupling protein (UCP), and adenosine monophosphate-dependent kinase (AMPK) α1 mRNA in the pectoralis and liver of Eurasian tree sparrows (Passer montanus) from high-altitude (3,230 m), medium-altitude (1400 m), and low-altitude (80 m) regions. Our results showed that high-altitude sparrows had greater body masses, longer wings and tarsometatarsi, but comparable bill lengths relative to medium- and low-altitude individuals. High-altitude sparrows had higher plasma T₃ levels and pectoralis muscle mitochondrial COX capacities than their lowland counterparts. They also upregulated the pectoralis muscle mRNA expression of UCP, PGC-1α, and ANT proteins relative to low-altitude sparrows. Unlike pectoralis, high-altitude sparrows significantly down-regulated hepatic AMPKα1 and ANT protein expression as compared with their lowland counterparts. Our results contribute to understanding the morphological, biochemical, and molecular adaptations in free-living birds to cope with the cold seasons in the extreme environment of the QTP.