Genetic architecture and adaptation of flowering time among environments

1. The genetic basis of flowering time changes across environments, and
pleiotropy may limit adaptive evolution of populations in response to
local conditions. However, little is known about how genetic architecture
changes among environments. 2. We used genome-wide association studies
(GWAS) in Boechera stricta (Graham) Al-Shehbaz, a relative of Arabidopsis,
to examine flowering variation among environments and associations with
climate conditions in home environments. Also, we used molecular
population genetics to search for evidence of historical natural
selection. 3. GWAS found 47 significant quantitative trait loci (QTLs)
that influence flowering time in one or more environments, control plastic
changes in phenology between experiments, or show associations with
climate in sites of origin. Genetic architecture of flowering varied
substantially among environments. We found that some pairs of QTLs showed
similar patterns of pleiotropy across environments. A large-effect QTL
showed molecular signatures of adaptive evolution and is associated with
climate in home environments. The derived allele at this locus causes
later flowering and predominates in sites with greater water availability.
4. This work shows that GWAS of climate associations and ecologically
important traits across diverse environments can be combined with
molecular signatures of natural selection to elucidate ecological genetics
of adaptive evolution.