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

Abstract

6Word count: 7 Running short title: Adaptation to stress in Brachypodium along aridity gradient. 8 9 2 Summary 1 0• Plants have diverse strategies to cope with stress, including early flowering to "escape" 1 1 abiotic stress and late flowering to mitigate biotic stress. Plants are usually exposed to 1 2 multiple stresses simultaneously, but little is known about the impact of multiple co-1 3 occurring stresses on plant evolution. 1 4 • We tested for adaptation to both aridity and interspecific competition of the model plant 1 5Brachypodium spp., collected along the aridity gradient in Israel. We recorded flowering 1 6 time and estimated fitness in a controlled watering experiment, with treatments mimicking 1 7Mediterranean and arid precipitation, and in two common gardens located in the extremes of 1 8 the gradient (i.e., desert and mesic Mediterranean). At the latter we also manipulated 1 9interspecific competition to examine the combined effect of competition and aridity. 2 0 • Plants from arid environments always flowered earlier, but we found no selection on 2 1 flowering time in the watering experiment. In the common gardens, however, the direction 2 2 of selection on flowering time differed between sites and competition treatments.2 3 • We conclude that interactions between aridity and competition drive local adaptation of 2 4 Brachypodium in the Eastern Mediterranean basin. Variation in flowering time is an 2 5important adaptive mechanism to aridity and multiple selection agents can have interactive 2 6 effects on the evolution of this trait. 2 7 2 8