Birds of the long-tailed family are all cute little ones. As a close relative, the brown-fronted long-tailed and the red-headed long-tailed are similar in appearance except for the different wear colors on their bodies.
However, the habitat of the two species of birds is very different: the brown-fronted long-tailed lives at a high altitude of 2,000 to 3,000 meters and comes and goes freely in the special environment of the Qinghai-Tibet Plateau; the red-headed long-tailed prefers the mountain forests and shrublands in the lower elevations.
Under the similar appearance, where is the difference?
Recently, the research team of Lei Fumin and Qu Yanhua, researchers at the Institute of Zoology of the Chinese Academy of Sciences, revealed the genetic mechanism of three species of plateau birds adapting to high-altitude environments, and the relevant results were published in the Proceedings of the National Academy of Sciences of the United States.
Discover the "secret weapon" of the highland birds
The Qinghai-Tibet Plateau is the largest plateau in China and the highest in the world, with an average altitude of 4500 meters. High altitude areas are hypoxic, low temperature, and strong ultraviolet radiation, and the hardiness, hypoxia resistance, and metabolic capacity of mammals and birds living here will be enhanced, and their weight will also increase.
Lei Fumin's research group published a study last year in the Proceedings of the National Academy of Sciences in the United States, which proved that the hemoglobin oxygen affinity of birds at high altitude on the Qinghai-Tibet Plateau was increased compared with their low-altitude relatives by comparing the functional phenotype and molecular structure of hemoglobin. Most of these functional changes are caused by different amino acid substitutions.
"In the past, most of the research on the adaptability of plateau organisms focused on phenotypes, such as body size, structural morphology, metabolic rate, etc." Hao Yan, the first author of the paper and a doctoral candidate at the Institute of Zoology of the Chinese Academy of Sciences, told China Science Daily, "This time we hope to reveal the genetic mechanism behind the convergence and evolution of these adaptive traits at the molecular level." ”
They selected three species of passeriformes from the high-altitude areas of the Tibetan Plateau – brown-crowned, black-crowned and brown-fronted long-tailed – and identified three closely related low-altitude species with the same genetic distance as each of them (the effect of different control of evolutionary time on genetic adaptation) – swamp, yellow-bellied and red-headed long-tailed.
The researchers performed deep transcriptome sequencing of five tissues, including heart, muscle, liver, lungs, and kidneys, of these six birds, and compared the differences in sequence levels and expression levels between high and low altitude species.
Share more than 200 "treasure" genes
By comparing and analyzing more than 7,000 genes shared by these birds, the researchers found that three high-altitude bird species shared as many as 218 so-called "positive selection genes" — genes that allow birds to improve their ability to survive or reproduce in special environments at high altitudes.
The researchers speculate that in addition to genetic variation, substitutions of specific amino acids may also contribute to the birds' ability to adapt to altitude life. But they then found that only 4 of the 3 high-altitude species contained the same amino acid replacement sites in their genes.
"Our results show that the high-altitude adaptive convergence of these species of birds is mainly manifested at the level of positive selection genes, rather than amino acid substitution." Hao Yan said.
Usually in multiple tissues of different species, there are two modes of tissue-specific expression and species-specific expression of genes. Tissue-specific expression patterns refer to gene expression in the same tissues of different species and should be more similar than different tissues within the same species. Species-specific expression patterns refer to gene expression in different tissues within the same species, which should be more similar than the same tissues between species.
The researchers performed clustering analyses of patterns of gene expression in all tissues. These data from the same tissues of different birds were pooled together, indicating a general pattern of tissue-specific expression. That is, there is a strong similarity in gene expression in the same tissue in different species of birds, suggesting that tissue differentiation may precede species differentiation.
The expression profiles of differentially expressed gene sets and altitude-related gene sets showed altitude-dependent clustering patterns, suggesting that the high-altitude environment may have driven similar expression changes in high-altitude species.
It helps to understand how species respond to high-altitude environments
These results reveal that three species of high-altitude birds may have evolved adaptively to their environment in a way that sequences and expression levels change in synergy.
Qu Yanhua, one of the corresponding authors of the paper, told China Science Daily: "Unlike other taxonomic high-altitude adaptation studies, our study for the first time carried out multi-species, multi-organization, multi-scale comparative analysis of wild birds with different relatives, expanding people's understanding of how species respond to high-altitude environments." ”
"The adaptive evolution of heredity is more influenced by phylogenetic relationships, i.e., the degree of similarity of genetic backgrounds, than the general convergence of trait evolution. This phenomenon applies not only to birds, but also to fauna. She said.
Related paper information:
DOI:10.1073/pnas.1819657116