Barriers to gene flow play an important role in the speciation of two
closely related Populus (Salicaceae) species
Abstract
Despite the growing number of recent studies on genome-wide divergence
during speciation, the genetic basis and mechanisms of genomic
divergence and speciation are still incompletely understood. In most
species, natural selection plays a key role in genomic heterogeneous
divergence. Additionally, barriers to gene flow, such as chromosomal
rearrangements or gene incompatibilities, can also cause genome
heterogeneity and speciation. Based on whole genome re-sequencing data
from 27 Populus alba and 28 P. adenopoda individuals, we explored the
reasons for the heterogeneous differentiation of genomes of these two
closely related species. The results showed that the two species
diverged ~5-10 million years ago (Mya), when the
Qinghai-Tibet Plateau reached a certain height and the inland climate of
the Asian continent became arid, which caused the two species begin to
diverge and eventually led to speciation. In highly differentiated
regions, neutrality tests (Tajima’s D and Fay & Wu’s H) of these
regions revealed no difference while the absolute divergence (dxy) were
significantly higher than genome background, which indicates that
barriers to gene flow rather than natural selection played a major role
in maintaining genomic heterogeneous divergence and reproductive
isolation, which is the most important condition for speciation. We
further found that some genes related to reproduction may be involved in
explaining the reproductive isolation of the two species.