Hybridization boosts dispersal of two contrasted ecotypes in a grass species

Abstract

Genetic exchanges between closely related groups of organisms with different adaptations have well-documented beneficial and detrimental consequences. In plants, pollen-mediated exchanges affect the sorting of alleles across physical landscapes and influence rates of hybridization. How these dynamics affect the emergence and spread of novel phenotypes remains only partially understood. Here, we use phylogenomics and population genomics to retrace the origin and spread of two geographically overlapping ecotypes of the African grass Alloteropsis angusta . In addition to an ecotype inhabiting wetlands, we report the existence of a previously undescribed ecotype inhabiting Miombo woodlands and grasslands. The two ecotypes are consistently associated with different nuclear groups, which represent an advanced stage of divergence with secondary low-level gene flow. However, the seed-transported chloroplast genomes are consistently shared by distinct ecotypes inhabiting the same region. These patterns suggest that the nuclear genome of one ecotype can enter the seeds of the other via occasional pollen movements with sorting of nuclear groups in subsequent generations. The contrasting ecotypes of A. angusta can thus use each other as a gateway to new locations across a large part of Africa, showing that hybridization can facilitate the geographical dispersal of distinct ecotypes of the same grass species.

Variation in the rate lateral gene transfers accumulate in a grass lineage

“…The time scale, in million years, is shown at the bottom. The species names are indicated near branches corresponding to their most recent common ancestor, as are those of the groups corresponding to the two ecotypes of A. angusta (‘ere’ = erect, ‘dec’ = decumbent [Curran et al 2022]), and the subclades of A. semialata (clades I to IV [Bianconi et al 2020]). Coloured bars on the right of the phylogenetic trees delimit the clades, with the grey bar within clade IV highlighting the accessions from Asia and Australia, when all others originate from Africa.…”

“…Our results moreover show that even if LGT are preferentially acquired by a given sublineage, such as ZAM1505, they can greatly contribute to the species-level pangenome (Figure 4) and might later be introgressed to other populations (Figure 1; see also Olofsson et al 2016). Indeed, the different sublineages of A. semialata and even the two sister species A. angusta and A. cimicina occasionally undergo gene flow (Olofsson et al 2016; Curran et al 2022), so that the standing variation created by LGT has the potential to fuel adaptation throughout the group.…”

Lateral gene transfer generates accessory genes that accumulate at different rates within a grass lineage

“…angusta and A . cimicina occasionally undergo gene flow (Olofsson et al ., 2016; Curran et al ., 2022) so that the standing variation created by LGT has the potential to fuel adaptation throughout the group.…”

“…1; Olofsson et al, 2016). Indeed, the different sublineages of A. semialata and even the two sister species A. angusta and A. cimicina occasionally undergo gene flow (Olofsson et al, 2016;Curran et al, 2022) so that the standing variation created by LGT has the potential to fuel adaptation throughout the group.…”