Adaptive phenotypic variation in a Mediterranean shrub: causes and consequences under realistic climate change environments

Abstract

Climate change is a complex phenomenon that causes shifts in precipitation and temperature patterns, imposing higher climatic heterogeneity and more severe and frequent extreme climatic events. The effects of climate change are expected to be particularly intense in the Mediterranean region, where drought is the main selective pressure and already imposes challenging conditions for plant populations. However, drought rarely acts in isolation, and climate change may further intensify the effects of other biotic and abiotic stressors. Specifically, the Mediterranean region is experiencing intense warming, and recent climatic projections forecast continued temperature increases with a higher frequency of more intense heatwaves in the next decades. Furthermore, these climatic changes are expected to disrupt diverse natural processes, such as plant-plant interactions. Altogether, these multiple co-occurring stressors may compromise the long-term persistence of Mediterranean plant populations. Among Mediterranean plants, gypsophiles — plants restricted to gypsum soils— may be especially vulnerable to future environmental changes since they already experience highly stressful conditions. In response to the new selective pressures imposed by climate change, plant populations may migrate to more suitable habitats and/or persist locally through adaptive evolution (i.e., evolution by natural selection), phenotypic plasticity (both within and across generations), or a combination of both processes. Because gypsophiles lack effective dispersal mechanisms and occur in highly fragmented habitats, their persistence may largely depend on in situ evolutionary processes rather than migration. Gypsophile populations have experienced different selective pressures during their evolutionary history, mainly related to climatic and edaphic conditions, which may have shaped intraspecific genetically-based phenotypic variation. Such phenotypic differences among populations driven by past selection may strongly affect the vulnerability of gypsophile populations and their future responses. In addition, the presence of concomitant stressors may modify population differentiation, adaptive plastic responses to drought, the patterns of selection and the presence of quantitative genetic variation within populations, which in turn may affect the ecological and evolutionary trajectories of Mediterranean gypsophiles. Therefore, assessing the causes of standing intraspecific phenotypic and genetic variation and how Mediterranean gypsophile populations will respond to complex environmental conditions is critical to understand the eco-evolutionary consequences and the future vulnerability of such populations in a climate change context.