Effects of Mountain Uplift and Climatic Oscillations on Phylogeography
and Species Divergence of Notholirion (Liliaceae)
Abstract
Exploring the geological events and climate change in the
Himalaya-Hengduan Mountains (HHM) region and the Qinghai-Tibet Plateau
(QTP) is crucial for understanding the impact of environmental change on
biogeographic distribution and biological evolution. To delve deeper
into these mechanisms, we reconstructed the evolutionary history of
three Notholirion species that span these regions. Here, we examined a
total of 254 individuals from 31 populations of these three species,
utilizing five chloroplast DNA (cpDNA) (matK, ndhA, ndhG-ndhI,
petB-petD, and petL-petG), along with one nuclear DNA region (internal
transcribed spacer, ITS). We identified 14 haplotypes from cpDNA and 27
haplotypes from the ITS, each specific to corresponding species. Robust
haplotype trees were detected, and obvious discrepancies were found
between the cpDNA and ITS trees. A total of 147 chloroplast genomes were
used for divergence time estimation, of which 10 chloroplast genomes
from distinct populations of Notholirion species provided a
comprehensive representation of the genus. The divergence time
estimation results suggested that species of Notholirion genus
originated in the southern Himalayan region during the Late Oligocene
period (25.05 Ma), and the three Notholirion species then diverged
during the Late Pliocene period (7.43 Ma). Our maximum model forecasts
that the overall distribution range of Notholirion over four different
periods remains relatively stable,from LIG to the future. The origin of
the genus Notholirion was triggered by sustained climate fluctuations
during the Late Oligocene, with the uplift of the Himalayas and the
subsequent orogenic movements intensifying climate changes and further
promoting the species divergence of Notholirion. A long evolutionary
history, coupled with sexual reproduction and habitat fragmentation,
likely contributed to the higher genetic diversity of Notholirion. The
higher genetic differentiation among Notholirion populations may be
attributed to drastic changes in the external environment within their
range, as well as their constrained capacity for seed production and
dispersal.