Genome‐wide analysis of butterfly bush (Buddleja alternifolia) in three uplands provides insights into biogeography, demography and speciation

• Published in: The New phytologist 2021-11, Vol.232 (3), p.1463-1476
• Main Authors: Ma, Yong‐Peng, Wariss, Hafiz Muhammad, Liao, Rong‐Li, Zhang, Ren‐Gang, Yun, Quan‐Zheng, Olmstead, Richard G., Chau, John H., Milne, Richard I., Van de Peer, Yves, Sun, Wei‐Bang
• Format: Article
• Language: English
• Subjects: Adaptation; allopatric speciation; Allopatry; Biogeography; Buddleja; Buddleja alternifolia; Chromosomes; Colour; Contraction; demographic history; Demography; Divergence; Ecological distribution; Ecological niches; Gene flow; Gene sequencing; Genomes; Geographical isolation; Kunlun–Yellow river tectonic movement; Loess Plateau; Mountains; Niches; Plant diversity; Plant species; Populations; Reflectance; Scrophulariaceae; Speciation; Tectonics; whole‐genome sequencing
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.17637

Summary Understanding processes that generate and maintain large disjunctions within plant species can provide valuable insights into plant diversity and speciation. The butterfly bush Buddleja alternifolia has an unusual disjunct distribution, occurring in the Himalaya, Hengduan Mountains (HDM) and the Loess Plateau (LP) in China. We generated a high‐quality, chromosome‐level genome assembly of B. alternifolia, the first within the family Scrophulariaceae. Whole‐genome re‐sequencing data from 48 populations plus morphological and petal colour reflectance data covering its full distribution range were collected. Three distinct genetic lineages of B. alternifolia were uncovered, corresponding to Himalayan, HDM and LP populations, with the last also differentiated morphologically and phenologically, indicating occurrence of allopatric speciation likely to be facilitated by geographic isolation and divergent adaptation to distinct ecological niches. Moreover, speciation with gene flow between populations from either side of a mountain barrier could be under way within LP. The current disjunctions within B. alternifolia might result from vicariance of a once widespread distribution, followed by several past contraction and expansion events, possibly linked to climate fluctuations promoted by the Kunlun–Yellow river tectonic movement. Several adaptive genes are likely to be either uniformly or diversely selected among regions, providing a footprint of local adaptations. These findings provide new insights into plant biogeography, adaptation and different processes of allopatric speciation.