Abstract
The South American temperate forests have been subjected to drastic past topographic and climatic changes during the Pliocene – Pleistocene linked to Andean orogeny and glacial cycles. These changes are common drivers of genetic structure and adaptation process. Embothrium coccineum, a member of the Proteaceae family and an emblematic tree of the South American temperate forest with a distribution spanning 20° of latitude, has been strongly affected by these topographic and climatic changes. Previous studies have shown that the species presents a marked genetic structure with distinct ecotypes described; yet, little is known about their adaptive genetic responses. The main goal of this study was to investigate the effects of historical and contemporary landscape features affecting the genetic diversity and connectivity of E. coccineum throughout its natural distribution. Using more than 2000 SNPs, two genetic groups (North and Center-South) that have diverged some 2.8 million years ago were observed. The level of genetic structure was higher between populations within the North genetic group than within the Center-South group. We propose that these contrasting patterns of genetic structure are related to differences in pollinator’s assemblage and evolutionary histories between genetic groups. Moreover, we observed the existence a strong patter of isolation by environment inE. coccineum , suggesting that selection could have leaded to adaptive divergence among localities. We propose that, within the Chilean temperate forest, the patterns of genetic variation in E. coccineum reflect both a Quaternary phylogenetic imprint and the impact of selection to the strong environmental gradient.
Keywords: Temperate forest - Population genomics - Proteaceae - Isolation by environment - Last Glacial Maxima - Divergence time
Editor in Chief
Ecology and Evolution
Dear Dr. Allen Moore,
I hope this cover letter finds you safe and healthy during these absolutely unprecedented pandemic times.
I wish to submit an original research article for publication in Tree Genetics and Genome, titled “Impact of pleistocene glaciations and environmental gradients on Embothrium coccineum genetic structure” . The paper was authored by Sepúlveda-Espinoza, F; Bertín-Benavides, A; Hasbún, R; Toro-Núñez, O; Varas-Myrik, A; Alarcón, D; and Guillemin, M-L. This study evaluated the effects of historical and contemporary landscape features affecting the genetic diversity and connectivity of E. coccineum throughout its natural distribution.Embothrium coccineum is an emblematic tree part of the Proteaceae familly and endemic to the South American temperate forests. Genotypes for more than 2000 SNPs were obtained for trees sampled throughout the complete natural distribution of the species. Results show the existence of two main genetic groups (North and Center-South) that diverged some 2.8 million years ago each characterized by distinct complex patterns of genetic divergence among populations with 1) a clear genetic isolation between populations located in the North and 2) a more homogeneous distribution of the genetic variation in the Center-South with a gradient of admixture between the North and Center-South genetic groups detected in the species center part of the distribution. These patterns reflect the clear impacts of past (Pliocene – Pleistocene) topographic and climatic changes, linked to Andean orogeny and glacial cycles, but also the possible importance of regional differences in pollinator’s assemblage leading to contrasting level of gene flow in the North and Center-South on E. coccineum populations. A strong signal of isolation by environment was also observed in E. coccineum , suggesting that selection could have led to adaptive divergence among localities. We propose that local adaptation in this species could be linked in particular to differential access to water during the driest months.
We believe that our study makes a significant contribution to the topics addressed by your journal. Indeed, this study is the first to present estimations of time of genetic divergence in E. coccineum but also allow to disentangle the effects of local adaptation and isolation by environment (IBE) from neutral processes, such as isolation by distance (IBD) or co-ancestry linked to the species glacial history (IBA), in shaping among-population genetic differentiation of this species. The identification and quantification of the environmental variables structuring population genetic variation could inform management decisions for conservation, restoration or reforestation purposes.
This manuscript has not been published or presented elsewhere in part or in its entirety and is not under consideration by another journal. We have read and understood your journal’s policies, and we believe that neither the manuscript nor the study violate any of these. We declare no conflicts of interest.
Thank you for your consideration.
Best regards.
Ariana Bertin-Benavides
ONG Conciencia Sur
Concepción