International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.3, 133-146 http://ecoevopublisher.com/index.php/ijmeb 140 populations of ancestral bird species, which over time diverged into distinct species due to the lack of interbreeding opportunities (Lei et al., 2014). This process is evident in the phylogeographic patterns observed in species such as the Tibetan snow finch and the Hume’s ground tit, which show significant genetic divergence corresponding to the geological events of the plateau (Qu et al., 2009). In addition to geographic isolation, climatic fluctuations during the Quaternary period have played a crucial role in driving speciation on the plateau. The repeated cycles of glaciation and deglaciation created dynamic environments that alternated between periods of isolation and secondary contact. During glacial periods, many species were forced into refugia, where isolated populations adapted to specific local conditions, leading to genetic divergence. When the glaciers retreated, some of these populations came into contact again, leading to hybridization and further diversification. This combination of isolation and hybridization has been a powerful driver of speciation in the region. For example, the Tibetan snowcock (Tetraogallus tibetanus) shows evidence of historical isolation during glacial periods followed by post-glacial range expansions and secondary contact, which have shaped its current genetic structure. These processes highlight the complex interplay between geological and climatic factors in shaping the unique avian diversity of the Qinghai-Tibet Plateau. 5.3 Factors driving endemism Several factors drive the high level of endemism observed among birds in the Qinghai-Tibet Plateau. One of the primary factors is the geological history of the region, particularly the uplift of the plateau. This uplift, which began around 50 million years ago and has continued intermittently, created a variety of unique and isolated habitats. These isolated environments acted as refugia during adverse climatic conditions, providing safe havens for species to survive and evolve independently. The topographical complexity resulting from the uplift facilitated allopatric speciation, where species diverge due to geographical barriers. This process is evident in many avian species that show significant genetic divergence corresponding to their isolated habitats (Lei et al., 2014). Additionally, the climatic oscillations of the Quaternary period further influenced these patterns by periodically isolating populations during glacial periods and allowing secondary contact during interglacial periods, promoting both vicariance and hybridization-driven speciation. Ecological factors also play a crucial role in driving endemism on the Qinghai-Tibet Plateau. The extreme and varied climatic conditions of the plateau have necessitated the development of unique adaptations among its avian species. This has led to niche specialization, where different species adapt to specific ecological niches, reducing competition and promoting coexistence. For example, the Tibetan snow finch and the rufous-necked snow finch exhibit distinct habitat preferences and dietary habits that allow them to coexist despite living in the same region (Li et al., 2020). Furthermore, the plateau’s isolation from other regions has limited gene flow from external populations, maintaining genetic distinctiveness and enhancing local adaptation. Human activities and climate change have also begun to influence these dynamics, altering habitats and shifting the distribution and survival of endemic species. Studies have shown that climate change has already affected the ranges of several vertebrate species on the plateau, emphasizing the need for ongoing conservation efforts to protect these unique and diverse avian populations (Jiang et al., 2023). 6 Evolutionary Adaptations to High-Altitude Environments 6.1 Physiological adaptations Birds inhabiting the high-altitude environments of the Qinghai-Tibet Plateau have developed several physiological adaptations to cope with hypoxia, extreme cold, and other harsh conditions. A key adaptation involves modifications in hemoglobin (Hb) function, which increases oxygen affinity and efficiency of oxygen transport. For instance, studies have shown that high-altitude passerine birds on the plateau have evolved increased Hb-O2 affinity through both parallel and divergent amino acid substitutions (Zhu et al., 2018). Additionally, genomic studies on Tibetan partridge have identified genes under positive selection related to hypoxia response, metabolism, and immune function, further highlighting the physiological adaptations to high-altitude living (Li et al., 2022).
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