Loss of function of adaptive traits, resulting in trait loss, is a common area of study inevolution. Traits with lost function are frequently lost but may also be reduced or completely maintained. The fate of traits with lost or decreased function rely on the interplay of three factors – selection, pleiotropy, and genetic drift. In most systems, the exact mechanisms of trait loss are unknown, including in the loss of short stamen in Arabidopsis thaliana on latitudinal and altitudinal clines. Previous observation has shown there to be more short stamens at higher latitudes and altitudes and fewer at lower latitudes and altitudes. This study seeks to investigate two possible hypotheses for the cause of these clines. First, that there is directional selection for more short stamens at higher latitudes and altitudes or for fewer short stamens at lower altitudes and latitudes. Second, that pleiotropy between short stamen number and another trait that varies on the same clines may be leading to indirect selection. To address these hypotheses, we measured a variety of traits on latitudinal and altitudinal clines, tested if they varied on those clines, examined correlations between these traits and short stamen number, and finally performed a fitness regression analysis. Overall, we find little evidence for pleiotropic correlations between short stamen number and any of the measured traits, as well as evidence of weak selection for fewer short stamens.
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