Hybridisation and chloroplast capture between distinct Themeda triandra lineages in Australia

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  • Luke T Dunning
    University of Sheffield
  • J. Olofsson
    University of Copenhagen
  • Alexander S. T. Papadopulos
  • Samuel G.S. Hibdige
    University of Sheffield
  • Oriane Hidalgo
    Institut Botànic de Barcelona
  • Ilia J. Leitch
    Royal Botanic Gardens, Kew
  • Paulo C. Baleeiro
    University of Queensland
  • Sinethemba Ntshangase
    University of Pretoria
  • Nigel Barker
    University of Pretoria
  • Richard W. Jobson
    Australian Institute of Botanical Science

Ecotypes are distinct populations within a species that are adapted to specific environmental conditions. Understanding how these ecotypes become established, and how they interact when reunited, is fundamental to elucidating how ecological adaptations are maintained. This study focuses on Themeda triandra, a dominant grassland species across Asia, Africa and Australia. It is the most widespread plant in Australia, where it has distinct ecotypes that are usually restricted to either wetter and cooler coastal regions or the drier and hotter interior. We generate a reference genome for T. triandra and use whole genome sequencing for over 80 Themeda accessions to reconstruct the evolutionary history of T. triandra and related taxa. Organelle phylogenies confirm that Australia was colonized by T. triandra twice, with the division between ecotypes predating their arrival in Australia. The nuclear genome provides evidence of differences in the dominant ploidal level and gene-flow among the ecotypes. In northern Queensland there appears to be a hybrid zone between ecotypes with admixed nuclear genomes and shared chloroplast haplotypes. Conversely, in the cracking claypans of Western Australia, there is cytonuclear discordance with individuals possessing the coastal chloroplast and interior clade nuclear genome. This chloroplast capture is potentially a result of adaptive introgression, with selection detected in the rpoC2 gene which is associated with water use efficiency. The reason that T. triandra is the most widespread plant in Australia appears to be a result of distinct ecotypic genetic variation and genome duplication, with the importance of each depending on the geographic scale considered.


  • adaptation, andropogoneae, angiosperms, ecological genetics, phylogeography, population genetics
Original languageEnglish
Pages (from-to)5846-5860
Number of pages15
JournalMolecular Ecology
Issue number22
Early online date12 Sep 2022
Publication statusPublished - Nov 2022
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