Hybridisation boosts dispersal of two contrasted ecotypes in a grass species

<p>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 <i>Alloteropsis angusta</i>. 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 <i>A. angusta</i> 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.</p>