High-altitude environments present strong stresses for living organisms, which have driven striking phenotypic and genetic adaptations. While previous studies have revealed multiple genetic adaptations in high-altitude species, how evolutionary history (i.e., phylogenetic background) contributes to similarity in genetic adaptations to high-altitude environments is largely unknown, in particular in a group of birds. We explored this in 3 high-altitude passerine birds from the Qinghai-Tibet Plateau and their low-altitude relatives in lowland eastern China. We generated transcriptomic data for 5 tissues across these species and compared sequence changes and expression shifts between high- and low-altitude pairs. Sequence comparison revealed that similarity in all 3 high-altitude species was high for genes under positive selection (218 genes) but low in amino acid substitutions (only 4 genes sharing identical amino acid substitutions). Expression profiles for all genes identified a tissue-specific expression pattern (i.e., all species clustered by tissue). By contrast, an altitude-related pattern was observed in genes differentially expressed between all 3 species pairs and genes associated with altitude, suggesting that the high-altitude environment may drive similar expression shifts in the 3 high-altitude species. Gene expression level, gene connectivity, and the interactions of these 2 factors with altitude were correlated with evolutionary rates. Our results provide evidence for how gene sequence changes and expression shifts work in a concerted way in a group of high-altitude birds, leading to similar evolution routes in response to high-altitude environmental stresses.

Net ecosystem exchange (NEE) of carbon dioxide (CO 2 ) was measured at Zoige wetland using the eddy covariance technique. Analysis of CO 2 fluxes in two years showed Zoige wetland was a net CO 2 sink of −47.1 and −79.7 gC m −2 a −1 in 2008 and 2009, respectively. The peak NEE value was −0.54 mg CO 2 m −2 s −1 (the negative value signifies net ecosystem carbon gain from air). The maximal daily integrated NEE was −4.1 gC m −2 d −1 during the peak growth season (from July to August). Gross ecosystem photosynthesis was likely more variable than ecosystem respiration at both seasonal and interannual timescales in this wetland. Our data strongly suggested that the combination of precipitation and temperature, as well as phenological stage of vegetation, controlled the dynamics of ecosystem carbon gain, even in drought years. Therefore, an accurate representation of these parameters in climate models is critical to the success of forecasting carbon budgets of alpine wetlands.

In the absence of nuclear-genomic differentiation between two populations, deep mitochondrial divergence (DMD) is a form of mito-nuclear discordance. Such instances of DMD are rare and might variably be explained by unusual cases of female-linked selection, by male-biased dispersal, by “speciation reversal” or by mitochondrial capture through genetic introgression. Here, we analyze DMD in an Asian Phylloscopus leaf warbler (Aves: Phylloscopidae) complex. Bioacoustic, morphological, and genomic data demonstrate close similarity between the taxa affinis and occisinensis, even though DMD previously led to their classification as two distinct species. Using population genomic and comparative genomic methods on 45 whole genomes, including historical reconstructions of effective population size, genomic peaks of differentiation and genomic linkage, we infer that the form affinis is likely the product of a westward expansion in which it replaced a now-extinct congener that was the donor of its mtDNA and small portions of its nuclear genome. This study provides strong evidence of “ghost introgression” as the cause of DMD, and we suggest that “ghost introgression” may be a widely overlooked phenomenon in nature.