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