Local adaptation to abiotic and biotic stresses and phenotypic selection on flowering time in annual Brachypodium spp. along an aridity gradient

Abstract

O_LIPlants have diverse strategies to cope with stress, including early flowering to \"escape\" abiotic stress and late flowering to mitigate biotic stress. Plants are usually exposed to multiple stresses simultaneously, but little is known about the impact of multiple co-occurring stresses on plant evolution.\nC_LIO_LIWe tested for adaptation to both aridity and interspecific competition of the model plant Brachypodium spp., collected along the aridity gradient in Israel. We recorded flowering time and estimated fitness in a controlled watering experiment, with treatments mimicking Mediterranean and arid precipitation, and in two common gardens located in the extremes of the gradient (i.e., desert and mesic Mediterranean). At the latter we also manipulated interspecific competition to examine the combined effect of competition and aridity.\nC_LIO_LIPlants from arid environments always flowered earlier, but we found no selection on flowering time in the watering experiment. In the common gardens, however, the direction of selection on flowering time differed between sites and competition treatments.\nC_LIO_LIWe conclude that interactions between aridity and competition drive local adaptation of Brachypodium in the Eastern Mediterranean basin. Variation in flowering time is an important adaptive mechanism to aridity and multiple selection agents can have interactive effects on the evolution of this trait.\nC_LI