Elevation as a selective force on mitochondrial respiratory chain complexes of thePhrynocephaluslizards in the Tibetan plateau

Abstract

Animals living in extremely high elevations have to adapt to low temperatures and low oxygen availability (hypoxia), but the underlying genetic mechanisms associated with these adaptations are still unclear. The mitochondrial respiratory chain can provide over 95% of the ATP in animal cells, and its efficiency is influenced by temperature and oxygen availability. Therefore, the respiratory chain complexes could be important molecular targets for positive selection associated with respiratory adaptation in high altitude environments. Here, we investigated positive selection in five respiratory chain complexes and their assembly factors by analyzing sequences of 106 genes obtained through RNA-seq of all 15 Chinese Phrynocephalus lizard species, which are distributed from lowlands to the Tibetan plateau (average elevation above 4500m). Our results indicate that evidence of positive selection on respiratory chain complex genes is not significantly different from assembly factors, and we found no difference in selective pressures among the five complexes. We specifically looked for positive selection in lineages where changes in habitat elevation happened. The group of lineages evolving from low to high altitude show stronger signals of positive selection than lineages evolving from high to low elevations. Lineages evolving from low to high elevation also have more shared codons under positive selection, though the changes are not equivalent at the amino acid level. This study advances our understanding of the genetic basis of animal respiratory metabolism evolution in extreme high environments, and provides candidate genes for further confirmation with functional analyses.

Gut Virome of the World’s Highest-Elevation Lizard Species ( Phrynocephalus erythrurus and Phrynocephalus theobaldi ) Reveals Versatile Commensal Viruses

“…The habitat elevation of Phrynocephalus lizards reaches the altitude of the Qinghai-Tibet Plateau (QTP), which is known as the “roof of the world” and has an average altitude of over 4,500 m ( 1 ). The Phrynocephalus genus contains over 40 species of toad-headed lizards, some of which are widely distributed in the QTP ( 2 ), including the species Phrynocephalus erythrurus and Phrynocephalus theobaldi , which are considered to be the highest-altitude lizard species in the world ( 3 ).…”

De novo Assembly, Annotation, and Analysis of Transcriptome Data of the Ladakh Ground Skink Provide Genetic Information on High-Altitude Adaptation

“…The genesis of the Tibetan highlands and the Himalayas since the Paleogene, with the Greater Himalayas starting to rise presumably the earliest in the post-Eocene (for a review, see the supplementary in Hofmann et al [ 2 ]), triggered the evolution of unique biodiversity under gradual high-altitude adaptation, as already shown for anurans [ 3 , 4 , 5 , 6 , 7 ]. Besides amphibians, there are also several reptiles that can cope with life at high altitude in those regions, e.g., Thermophis [ 8 ], Phrynocephalus [ 9 ], and some Laudakia species [ 10 ]. Potential constraints to upslope migration of reptiles (and amphibians) to high-elevation environments are the substantial UV-radiation, the thermal extremes, and especially the oxidative stress, referred to as high-altitude hypoxia, which interacts with temperature in a context-dependent manner to influence thermal performance and limits in terrestrial ectotherms [ 11 , 12 ].…”