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Hybridisation boosts dispersal of two contrasted ecotypes in a grass species

By Emma V. Curran, Matilda S Scott, Jill K Olofsson, Florence Nyirenda, Graciela Sotelo, Matheus E. Bianconi, Sophie Manzi, Guillaume Besnard, Pascal-Antoine Christin

Posted 18 Apr 2021
bioRxiv DOI: 10.1101/2021.04.16.440116

In the absence of strong reproductive barriers, 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. We use phylogenomics and population genomics to retrace the origin of two geographically overlapping ecotypes of the African grass Alloteropsis angusta. We report the existence of a previously undescribed ecotype inhabiting miombo woodlands and grasslands. The two ecotypes have divergent nuclear genomes. 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 pollen movements, with strong selection subsequently sorting nuclear alleles by habitat. The contrasting ecotypes of A. angusta can use each other as a gateway to new locations across a large part of Africa. Coupled with newly discovered hybridisation with the sister species A. semialata, our results show that hybridisation can facilitate the geographical dispersal of distinct ecotypes of the same grass species.

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