Demographic History among Aquilegia viridiflora
The lower eudicot genus Aquilegia , which represents a
phylogenetic midpoint between model species such as Arabidopsisand Oryza and has recently undergone adaptive radiation
evolution, has become an ideal model to study adaptive speciation.
Although A. viridiflora has a wide distribution and obvious
morphological differences, phylogenetic analysis based on the genome
showed that 20 populations constituted a fully supported monophyletic
clade in our study. Both the ML tree and PCA showed four groups withinA. viridiflora . Additionally, the optimum K value according to
the ADMIXTURE result was 4 (Figure 2 and Figure S2A), which verified the
existence of four groups. The degree of genome differentiation was low
(Fst values were all less than 0.25), indicating that A.
viridiflora is a “species on the speciation way”. Additionally, the
gene flow from warm and humid regions (EL and CN) to cold and arid
regions (NE) was greater than that in the opposite direction, which was
in accord with studies different populations of Silene ciliata ,Pseudotsuga menziesii and Eperua falcata (Brousseau, Fine,
Dreyer, Vendramin, & Scotti, 2021; George et al., 2021; Morente‐López
et al., 2021). This gene flow pattern was beneficial to increase the
genetic diversity of A. viridiflora in cold and arid environments
to enhance its local adaptability and accelerate speciation. The
demographic history analysis showed that A. viridifloradifferentiated into two lineages, eastern and western, at 6.45 Mya.
Subsequently, the eastern lineage differentiated into two groups, NE and
EL, at 5.97 Mya, and the western lineage differentiated into CN and NW
groups, at 5.54 Mya (Figure 3B). The divergence times of these groups
were all in the late Miocene. At this time, a global cooling event (late
Miocene coding, LMC) caused by the uplift of the northeastern part of
the Qinghai-Tibet Plateau and a general climate pattern of monsoons in
eastern China and arid inland areas in northwestern China formed (Chen
et al., 2019; Steinthorsdottir et al., 2021). Environmental changes in
the late Miocene also drove the lineage differentiation of thePsammobates tentorius complex and angraecoids in Africa
(Farminhão et al., 2021; Zhao, Heideman, Bester, Jordaan, & Hofmeyr,
2020). Therefore, temperature may be a critical driving force for the
differentiation of A. viridiflora . The group in
northwestern
China presented a high level of nucleotide polymorphism and a low level
of linkage disequilibrium, deducing that northwestern China may be the
origin region of A. viridiflora . These groups differentiated in
the late Miocene, when one branch migrated to the North China region and
the other branch migrated to the northeastern region. The group in the
northeastern region then diverged and migrated southward, forming a
group in the East Shandong South Liaoning area.