The plastid capture history of the subsect. Campylolepides and the section Ilex (Fagaceae: Quercus)

Abstract: The Quercus subsect. Campylolepides contains three species: Q. acutissima Carruth., Q. variabilis Blume and Q. chenii Nakai, which is the East Asian clade of Quercus section Cerris. Species formation and phylogeography of whole subsection or species within the subsection have been studied in detail. It was also found that the Q. section Cerris had an ancient gene introgression with the Q. section Ilex, which led to the plastid capture. However, the specific evolutionary history of plastids in Q. subsect. Campylolepides and Q. section Ilex remains unclear. Our study performed low-coverage whole genome sequencing on 15 samples from Q. section Ilex and integrated previously published data from Q. subsect. Campylolepides and its relatives, resulting in a total of 325 resequencing data, of which 276 individuals were from three Q. subsect. Campylolepides species and 19 populations. We assembled 325 plastids to perform phylogeographic analysis. The results were as follows: (1) There are shared haplotypes among three species of Q. subsect. Campylolepides, but the plastid haplotypes of the entire Q. Subsect.Campylolepides form a monophyletic branch nested within the Q. section Ilex species which are distributed from central China to Liangshan, Sichuan. (2) A relict haplotype of Q. subsection. Campylolepides from the Liaodong Peninsula clustered with Q. pseudosetulosa Q.S.Li & T.Y.Tu, a specie of the Q. section Ilex. (3) Both plastid capture events occurred in the middle Miocene, after which no plastid capture occurred between Quercus Subsect. Campylolepides and Quercus section Ilex. It is hypothesized that Q. subsect. Campylolepides and Q. section Ilex have formed almost complete reproductive isolation.