Author Affiliation:
1Department of Biological Science, Northern Arizona
University, Flagstaff, AZ 86011, USA2Center for Adaptable Western Landscapes, Northern
Arizona University, Flagstaff, AZ 86011, USA
3School of Earth and Sustainability, Northern Arizona
University, Flagstaff, AZ 86011, USA
4School of Forestry, Northern Arizona University,
Flagstaff, AZ 86011, USA
5Department of Research, Conservation and Collections,
Desert Botanical Garden, Phoenix, AZ, 85008, USA
Corresponding author: Hillary F. Cooper; telephone :
(510) 735-6130, email : Hillary.Cooper@nau.edu
Keywords: divergent selection, phenotypic plasticity,
QST-FST, Populus fremontii , local
adaptation, climate changeAbstract:
Selection on quantitative traits
by divergent climatic conditions can lead to substantial trait variation
across a species range. In the context of rapidly changing environments,
however, it is equally important to understand selection on trait
plasticity. To evaluate the role of selection in driving divergences in
traits and their associated plasticity within a widespread species, we
compared molecular and quantitative trait variation in Populus
fremontii (Fremont cottonwood) populations throughout Arizona. Using
SNP data and genotypes from 16 populations reciprocally planted in three
common gardens, we first performed
QST-FST analyses to detect selection on
traits and trait plasticity. We then explored the mechanistic basis of
selection using trait-climate and plasticity-climate regressions. Three
major findings emerged: 1) There was significant genetic variation in
traits expressed in each of the common gardens and in the phenotypic
plasticity of traits across gardens. 2) Based on
QST-FST comparisons, there was evidence
of selection in all traits measured; however, this result varied from no
effect in one garden to highly significant in another, indicating that
detection of past selection is environmentally dependent. We also found
strong evidence of divergent selection on plasticity across environments
for two traits. 3) Traits and/or their plasticity were often correlated
with population source climate (R2 up to 0.77 and
0.66, respectively). This suggests that steep climate gradients across
the Southwest have played a major role in shaping the evolution of
divergent phenotypic responses in populations and genotypes now
experiencing climate change.