Genomic insights into the evolutionary history and conservation of the living fossil Tetracentron sinense.

Tetracentron sinense is a 'living fossil' tree in East Asia. Understanding how this 'living fossil' responds to climate change and adapts to local environments is critical for its conservation. Here, we used re-sequenced genomes to clarify the evolutionary history and adaptive potential of T. sinense. We identified six divergent lineages in T. sinense: three lineages from southwestern China (Yunnan Province) and three lineages from the central subtropical region of China. Additionally, we detected hybridization events between some adjacent lineages. Demographic analysis revealed that over the past 10,000 years the effective population size (Ne) of three T. sinense lineages (i.e., NORTH, SWEST, and YNWEST) increased after their last bottleneck and then remained stable, whereas that of the remaining three lineages (i.e., YSEAST, YC, and EAST) declined steadily. The decline in effective population size in the Yunnan lineages aligned well with the decrease in genome-wide diversity and a significant increase in the frequency of runs of homozygosity. Deleterious variants and positively selected sites were involved in the evolution of different lineages. Further, genotype-environment association (GEA) analyses indicated adaptation to temperature- and precipitation-related factors. Genomic offset analyses found the most vulnerable populations, while SC and SC-yad were predicted to better handle extreme changes. Our findings provide insights into the evolutionary history and conservation of T. sinense and enhance our understanding of the evolution of living fossil species.