Evaluating the roles of drift and selection in trait loss along an elevational gradient

Traits that have lost function sometimes persist through evolutionary
time. Persistence may occur if there is not enough standing genetic
variation for the trait to allow a response to selection, if selection
against the trait is weak relative to drift, or if the trait has a
residual function. To determine the evolutionary processes shaping whether
nonfunctional traits are retained or lost, we investigated short stamens
in 16 populations of Arabidopsis thaliana along an elevational cline in
northeast Spain. A. thaliana is highly self-pollinating and prior work
suggests short stamens do not contribute to self-pollination. We found a
cline in short stamen number from retention of short stamens in high
elevation populations to incomplete loss in low elevation populations. We
did not find evidence that limited genetic variation constrains short
stamen loss at high elevations, nor evidence for divergent selection on
short stamens between high and low elevations. Finally, we identified loci
associated with short stamens in northeast Spain that are different from
loci associated with variation in short stamens across latitudes from a
previous study. Overall, we did not identify the evolutionary mechanisms
contributing to an elevational cline in short stamen number so further
research is clearly warranted. This dryad dataset includes the GWAS output
results. See the github for phenotypic data and SRA for genotypic data.