Format: ORAL

Fengmao Yang1,2, Jia Ge1,2

1Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, Yunnan, China 2Yunnan Key Laboratory for Integrative Conservation of Plant Species with Extremely Small Populations, Kunming Institute of Botany, Chinese Academy of Sciences (CAS), Kunming 650201, Yunnan, China

Background and Aims: Species of the genus Buddleja in Asia are mainly distributed in the Sino-Himalayan region and form a challenging taxonomic group, with extensive hybridization and polyploidization. A phylogenetic approach to unravelling the history of reticulation in this lineage will deepen our understanding of the speciation in biodiversity hotspots. Methods: For this study, we obtained 80 accessions representing all the species in the Asian Buddleja clade, and the ploidy level of each taxon was determined by flow cytometry analyses. Whole plastid genomes, nuclear ribosomal DNA, single nucleotide polymorphisms and a large number of low-copy nuclear genes assembled from genome skimming data were used to investigate the reticulate evolutionary history of Asian Buddleja. Complex cytonuclear conflicts were detected through a comparison of plastid and species trees. Gene tree incongruence was also analysed to detect any reticulate events in the history of this lineage. Key Results: Six hybridization events were detected, which are able to explain the cytonuclear conflict in Asian Buddleja. Furthermore, PhyloNet analysis combining species ploidy data indicated several allopolyploid speciation events. A strongly supported species tree inferred from a large number of low-copy nuclear genes not only corrected some earlier misinterpretations, but also indicated that there are many Asian Buddleja species that have been lumped mistakenly. Divergent time estimation shows two periods of rapid diversification (810 and 03 Mya) in the Asian Buddleja clade, which might coincide with the final uplift of the Hengduan Mountains and Quaternary climate fluctuations, respectively. Conclusions: This study presents a well-supported phylogenetic backbone for the Asian Buddleja species, elucidates their complex and reticulate evolutionary history and suggests that tectonic activity, climate fluctuations, polyploidization and hybridization together promoted the diversification of this lineage.