Discussion
Previous studies based on allozymes genotypes or chloroplast sequences (Mathiasen et al., 2007; Souto and Premoli, 2007; Vidal-Russell et al., 2011; Souto and Smouse, 2014) have reported genetic structure inE. coccineum . However, the limited variability and genome coverage of the markers used in previous studies has led to a lack of clarity regarding the species genetic structure as well as the processes that has shaped it. In the present study, samples of E. coccineum , including localities from its whole distribution range along the Chilean temperate forest, were genotyped through GBS to investigate patterns of genetic variation and their possible drivers using genome-wide data in this emblematic Chilean tree. The thousands of loci successfully genotyped provided a much better resolution of E. coccineum population genetic structure than the one obtained for the previously used molecular markers. First, our data showed the existence of two main lineages, North and Center-South. The existence of two genetic groups was already reported in the study of Souto and Premoli (2007), but the GBS data set also uncovered fine-scale genetic differentiation, especially in the northern part of the distribution. Inference of divergence time between these two genetic groups suggested that intraspecific divergence occurred some 2,8 Myrs ago, at the beginning of the Pleistocene, driven by climatic changes linked to glacial cycles. Moreover, the heterogeneous environment characterizing the South American temperate forests have been recognized as major driver explaining the actual genetic makeup of various plants and animals (Premoli et al., 2000) and could also have leaded to adaptive divergence among localities in E. coccineum . The strong IBE pattern detected in E. coccineum could indeed reflect the impact of actual gradient of temperature, precipitation and elevation, characteristic of the species distribution range, on its genetic diversity. These results suggest that selection, linked to the strong environmental gradient, could have leaded to adaptive divergence among localities.