Hybridisation boosts dispersal of two contrasted ecotypes in a grass species

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 hybridisation.
How these dynamics affect the emergence and spread of novel ecological
strategies 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. Besides 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
reach 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 hybridisation can facilitate the
geographical dispersal of distinct ecotypes of the same grass species.