Subgenome composition of hybrids and allopolyploids drives
genetic differentiation between groups
Interspecific hybridization and gene flow can introduce alleles into a
population, which can potentially result in adaptation to novel
environmental conditions. Previous work identified apparent admixture
between salt-tolerant P. vaginatum and non-tolerant P.
distichum , which could produce genotypes adapted to intermediate
salinity levels (Eudy, Bahri, Harrison, Raymer, & Devos, 2017). We
found that the two ecotypes of P. vaginatum and P.
distichum formed distinct genetic groups, with no signatures of gene
flow between P. vaginatum and P. distichum (Fig. 3, Fig.
S3), although we did identify limited gene flow between the coarse- and
fine-textured ecotypes of P. vaginatum (Fig. S4). It is
possible that ploidy differences between P. distichum (5x and 6x)
and P. vaginatum (2x and 3x) represent a sufficient reproductive
barrier to prevent gene flow.
While we did not find evidence for interspecific hybridization in the
wild between P. distichum and P. vaginatum , both the
coarse-textured and P. distichum groups appear to have been
formed from interspecific hybridization between fine-textured P.
vaginatum and other Paspalum species. Interestingly,
coarse-textured P. vaginatum and P. distichum do not
appear to share the same non-P. vaginatum subgenome (Fig. S5).
This difference in subgenome composition is thus likely the result of
hybridization between P. vaginatum and at least two differentPaspalum species.
Niche differentiation between these two hybrid groups could be due to
the genomic contribution of these non-P. vaginatum parents. To
our knowledge, no Paspalum species is as salt-tolerant asP. vaginatum ; therefore, it is likely that the non-P.
vaginatum parental species of both groups are not halophytic. Despite
this, coarse-textured P. vaginatum largely maintained its high
salt tolerance while P. distichum shows adaptations for
freshwater environments. Hypotheses for why this might have occurred
include lower expression of the P. vaginatum subgenome inP. distichum relative to coarse-textured P. vaginatum ,
differences in salt tolerance between the non-P. vaginatumparents, and post-hybridization selection for freshwater adaptations inP. distichum .