The role of reticulation in the rapid diversification of organisms is attracting greater attention in evolutionary biology. However, no empirical study has yet indicated how introgression across the genome may have altered the genetic composition of recipient taxa and increased their divergence within a species complex during the course of its evolution.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and Sichuan University used the Picea likiangensis species complex of spruce taxa as a system for testing if evolutionary divergence within this complex followed a reticulate or tree‐like pattern. They also wanted to clarify the role of introgression in promoting differentiation between diverging taxa.
The researchers used population genomic analysis combined with tests of different evolutionary scenarios using coalescent simulations.
The results showed that the Picea likiangensis complex, comprising three varieties of P. likiangensis (vars. likiangensis, linzhiensis, and rubescens) and one variey of P. brachytyla (var. complanata), originated rapidly at the end of the Pliocene and beginning of the Pleistocene.
The four taxa came into secondary contact during the mid‐Pleistocene and that their divergence, thereafter, has been influenced by hybridization and gene exchange.
Some introgressed alleles reached high frequencies in certain taxon pairs (vars. complanata and likiangensis, and vars. rubescensand linzhiensis, respectively) causing both taxa of such pairs to show increased divergence when compared with other taxa of the complex in which the same alleles were at low frequency or absent.
“Our analysis has provided a deeper understanding of the reticulate relationships among the four taxa comprising the P. likiangensis complex, and how reticulate evolution within the complex may have been affected by climatic oscillations and geological changes that occurred in the Hengduan and Himalayan regions during the Pleistocene” said Dr. Sun Yongshuai, first author of the study.