Reticulate speciation caused by interspecific hybridization is now recognized as an important mechanism in the creation of biological diversity. However, depicting the patterns of phylogenetic networks for lineages that have undergone interspecific gene flow is challenging.
By using genome-wide sequencing, the researchers from both the South China Botanical Garden and the Wuhan Botanical Garden sequenced 25 taxa representing natural diversity in the genus Actinidia with an average mapping depth of 26x on the reference genome to reconstruct their reticulate history.
They found evidence, including significant gene tree discordance, cytonuclear conflicts, and changes in genome-wide heterozygosity across taxa, collectively supporting extensive reticulation in the genus. Furthermore, at least two separate parental species pairs were involved in the repeated origin of the hybrid lineages, in some of which a further phase of syngameon was triggered.
On the basis of the elucidated hybridization relationships, the researchers further obtained a highly resolved backbone phylogeny consisting of taxa exhibiting no evidence of hybrid origin. The backbone taxa have distinct demographic histories and are the product of recent rounds of rapid radiations via sorting of ancestral variation under variable climatic and ecological conditions.
The results suggest a mode for consecutive plant diversification through two layers of radiations, consisting of the rapid evolution of backbone lineages and the formation of hybrid swarms derived from these lineages.
This research was directed by the Prof. Hongwen Huang from the South China Botanical Garden and Dr. Yifei Liu from the South Chian Botanical Garden, Dr. Dawei Li, Dr. Qiong Zhang and Dr. Caihong Zhong from the Wuhan Botanical Garden were the joint first author.
This work was supported by the Science and Technology Service Network Initiative of the Chinese Academy of Sciences (KFJ-EW-STS-076), the National Natural Science Foundation of China (31471847 and 31572092), and the Crop Germplasm Conservation Project of China (2016NWB027).