Adaptability of forest trees to climate – what can we learn from their evolutionary history
INRA, UMR BIOGECO, 33610 Cestas, France
Trees have experienced during the Pleistocene recurrent environmental changes over long time periods during the glacial-interglacial sequences. There is a growing body of evidence stemming from different sources of information (Quaternary evolutionary history; observations from population and species transfers; provenance experiments) showing that trees responded and adapted rapidly to these changes. This review aims at reconstructing the historical trajectories during the last interglacial period in order to decipher evolutionary processes triggering adaptation. Taking oaks as a study case, the review shows that rapid migration, extensive gene flow and hybridization were the main processes that permitted oak to track climatic warming. I will further address adaptive differentiation by considering separately differentiation of traits and genes controlling these traits, and investigate the pace at which adaptive differentiation occurred. There is concordant evidence between different sources of data that extant differentiation of adaptive traits was mainly generated during the late holocene, and that preexisting divergence due to population separation into refugia has been erased by extensive gene flow occurring during colonization. Additionnal results coming from simulations reconstructing in silico historical scenario also indicate that adaptive differentiation occurred rapidly. Overall this review suggests that substantial future evolutionary shifts can be expected in response to ongoing climate change due to the high level of genetic diversity existing in forest trees, and that gene flow will be an important driver of adaptive evolution.