Aim Montane regions like the Sino-Himalayas constitute global diversity hotspots. Various mechanisms such as in situ adaptive divergence, speciation following immigration or allopatric diversification in complex landscapes have been proposed to account for the exceptional diversity found in a particular clade in a montane setting. We investigated macroevolutionary patterns to test these different hypotheses in the continental radiation of a Sino-Himalayan bird group, the parrotbills (Paradoxornithidae).Location Sino-Himalayan region, Indo-Burma.Methods We used phylogenetic comparative methods based on a multilocus, time-calibrated phylogeny to reconstruct patterns of lineage diversification, biogeographical history, morphological evolution as well as of climate niche history using ecological niche modelling.Results The radiation of parrotbills started c. 12 Ma, diversifying at an apparent constant rate over time. The biogeographical history appears to be complex, within-region speciation in mountains was restricted to China. Size evolution was concentrated in the early phase of parrotbill radiation, whereas morphological shape evolution did not differ from Brownian motion. We found no indication for niche conservatism, with climate niche evolution occurring throughout the radiation of parrotbills.Conclusions Parrotbills diversified within a time span of increased regional orogenesis and associated strong climate change. While the south-west and central Chinese mountains were revealed to be a species pump, with in situ allopatric diversification triggered by complex topography and high habitat turnover, the diversity in the Himalayas was chiefly the result of immigration. Evidence for continuous ecological specialization and for the absence of climate niche conservatism could be interpreted as the consequence of ongoing climate-and habitat-induced ecological opportunities. The radiation of parrotbills demonstrates the influence of multiple drivers of diversification in a single group due to the dynamic geological and palaeoclimatic history of the SinoHimalayan region and illustrates the complex nature of continental radiations.

Sex chromosomes often bear distinct patterns of genetic variation due to unique patterns of inheritance and demography. The processes of mutation, recombination, genetic drift and selection also influence rates of evolution on sex chromosomes differently than autosomes. Measuring such differences provides information about how these processes shape genomic variation and their roles in the origin of species. To test hypotheses and predictions about patterns of autosomal and sex‐linked genomic diversity and differentiation, we measured population genetic statistics within and between populations and subspecies of the barn swallow (Hirundo rustica) and performed explicit comparisons between autosomal and Z‐linked genomic regions. We first tested for evidence of low Z‐linked genetic diversity and high Z‐linked population differentiation relative to autosomes, then for evidence that the Z chromosome bears greater ancestry information due to faster lineage sorting. Finally, we investigated geographical clines across hybrid zones for evidence that the Z chromosome is resistant to introgression due to selection against hybrids. We found evidence that the barn swallow mating system, demographic history and linked selection each contribute to low Z‐linked diversity and high Z‐linked differentiation. While incomplete lineage sorting is rampant across the genome, our results indicate faster sorting of ancestral polymorphism on the Z. Finally, hybrid zone analyses indicate barriers to introgression on the Z chromosome, suggesting that sex‐linked traits are important in reproductive isolation, especially in migratory divide regions. Our study highlights how selection, gene flow and demography shape sex‐linked genetic diversity and underlines the relevance of the Z chromosome in speciation.

Summary Knowledge about changes in plant functional traits is valuable for the mechanistic understanding of warming effects on ecosystem functions. However, observations have tended to focus on aboveground plant traits, and there is little information about changes in belowground plant traits or the coordination of above‐ and belowground traits under climate warming, particularly in permafrost ecosystems. Based on a 7‐yr field warming experiment, we measured 26 above‐ and belowground plant traits of four dominant species, and explored community functional composition and trait networks in response to experimental warming in a permafrost ecosystem on the Tibetan Plateau. Experimental warming shifted community‐level functional traits toward more acquisitive values, with earlier green‐up, greater plant height, larger leaves, higher photosynthetic resource‐use efficiency, thinner roots, and greater specific root length and root nutrient concentrations. However, warming had a negligible effect in terms of functional diversity. In addition, warming shifted hub traits which have the highest centrality in the network from specific root area to leaf area. These results demonstrate that above‐ and belowground traits exhibit consistent adaptive strategies, with more acquisitive traits in warmer environments. Such changes could provide an adaptive advantage for plants in response to environmental change.

In the study, thin AlxGa1−xN back barrier layer (BBL) with different Al composition (x) was employed in AlGaN/GaN HEMTs with GaN/AlN SLs schemes on Si substrate. The AlGaN BBL with low Al content (x < 0.15) has no significant effect on the crystalline quality, while a higher Al content will induce more dislocations and cause surface defects. The DC I–V characteristics show that AlGaN BBL (x = 0.1 and 0.15) is beneficial for obtaining high Ion/Ioff ratio of 108 and improving the off‐state behaviors with lower leakage current and higher breakdown voltage. The dynamic RON measurements were performed by applying the drain pre‐bias switching and different quiescent bias pulse tests. It is shown that the AlGaN BBL can effectively suppress the RON, dynamic degradation, due to that the channel electrons trapped in the C‐doping buffer were reduced by mitigating the electrons spill‐over effect under the strong off‐state bias. However, the device with higher Al‐content AlGaN BBL exhibits a rising RON, dynamic caused by the surface defects related traps. Overall, the devices with 0.1 and 0.15 Al‐content AlGaN BBL have an optimal performance.