Multiple origins of the desert shrub Reaumuria songarica in northern Xinjiang involving homoploid and tetraploid hybrids

Reaumuria songarica is a constructive shrub widely distributed
in temperate deserts of arid Central Asia. Previous studies
inferred that the populations of R. songarica in the Gurbantunggut Desert
(GuD) originated from homoploid hybridizations between its
eastern and western lineages and may have evolved into an incipient
species. To further reveal the genetic composition of different hybrid
populations and determine the species boundary of this independent hybrid
lineage, we hereby investigated the overall
phylogeographic structure of R. songarica based on
variation patterns of five cpDNA sequences and one nrITS
sequence in 32 populations. Phylogenetic analyses demonstrated
that in the GuD lineage, the Wuerhe
population evolved directly from the ancestors, whereas the
others were derived from hybrids between the eastern and western lineages.
PCoA and genetic barrier analysis strongly supported that the GuD
lineage was further divided into two genetic groups: the
southern group near the Tianshan Mountains (GuD-S) and
the northern group (GuD-N). The populations in GuD-S group had
consistent genetic composition and the same ancestral parents, indicating
that they belong to the homoploid hybrid lineage. However, the mixed GuD-N
group had undergone genetic admixture of the eastern and western lineages
on nrITS and cpDNA, and some populations were allopolyploid.
Additionally, BEAST analyses revealed that the
origins of the GuD-S and GuD-N
groups were later than 0.5 Ma.