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.