5 Conclusion
In conclusion, our study on the genetic diversity and structure ofNotholirion sheds light on the intricate evolutionary history and
adaptive mechanisms of this genus. The observed high genetic diversity
of Notholirion , surpassing the average of angiosperms, is
attributed to ITS early divergence in the late Oligocene andITS adaptation to diverse climatic and geological events duringITS evolution. The unique ”sky island” environments, resulting
from complex topography in the Himalayan-Hengduan Mountains, contribute
to the isolation of populations and, consequently, high genetic
differentiation. The AMOVA analyses revealed substantial genetic
variation among Notholirion populations, indicating limited
communication between populations due to specific habitat requirements,
restricted seed dispersal, and environmental factors influencing gene
flow. This genetic differentiation is consistent with the impact of
complex geological activities and climate changes in the
Himalayan-Hengduan Mountains region. Phylogenetic analysis confirmed the
monophyletic nature of Notholirion , with N. thomsonianumidentified as the earliest divergent taxon. However, incongruences
between nuclear and chloroplast gene trees suggest the influence of
incomplete lineage sorting and hybridization, common phenomena in plant
phylogenetics. The origin and diversification of Notholirion are
closely tied to the uplift events on the Tibetan Plateau. The late
Miocene and Pleistocene periods played pivotal roles in the evolution
and distribution of Notholirion species, with significant climate
fluctuations contributing to species divergence. The Last Glacial
Maximum, in particular, led to the formation of distinct species,
emphasizing the impact of Quaternary Ice Age climate changes on plant
ranges and population dynamics. Our findings propose thatNotholirion , as a high-altitude taxon, survived the ice age
through persistence in multiple refugia, particularly in the Hengduan
Mountains region. The study challenges previous assumptions about the
uniformity of ice cap coverage in the Tibetan Plateau and Hengduan
Mountains during the Quaternary period, suggesting a more nuanced
response of cold-tolerant plant taxa to climate changes. Overall, this
research contributes valuable insights into the evolutionary and
ecological dynamics of Notholirion , highlighting the importance
of considering multiple factors, including geological events, climatic
changes, and specific ecological, in understanding the genetic diversity
and adaptive strategies of high-altitude plant taxa.