Mechanisms of adaptation to Climate Change: how will phenotypic plasticity, microevolution and migration affect forest trees phenology ? – MeCC

The originality of our project lies in (i) integrating different adaptation mechanisms in ecological forecasts of climate change, which has only rarely been attempted; (ii) studying the interaction between these different mechanisms of adaptation, (iii) combining different types of modeling approaches and observations to both explore and predict the adaptive challenges and responses of tree populations experiencing climate changes. More precisely, we will make an original use of extant process-based models simulating variation in bud burst date and its impact on demographic rates, to quantitatively predict the direction and force of selection acting on phenological traits across environments in current and future climate. We will then incorporate this refined understanding of selection pressures in realistic ecological scenarios in quantitative genetics models of variable complexity to predict the joint changes in phenotypic and genetic values for bud burst dates. These predictions will be derived for a set of locations where the genetic and plastic variation in bud burst date are intensively studied, allowing quantitative tests of our predictions, as a validation step. To reach such objectives, our consortium gathers both modelers and experimentalists with complementary expertise in ecology, ecophysiology, quantitative genetics and evolutionary biology. The level of integration among the different tasks is very high. Results will (i) provide answers to fundamental questions about the evolution and adaptive value of phenotypic plasticity in variable environments, (ii) scenarios of range shift of forest tree species integrating adaptation processes and (iii) recommendations for forestry practices to manage the adaptive potential of forest tree species.

After 18 monthes, we obtained several preliminary results of interest.
We predict that sensitivity of bud burst date to temperature can help forest trees persist under future climate, but not for all species, nor all populatiions within a species range. In particular bud dormancy breakage by low tempretaures may become severely limiting for trees adapted to cold climates.
Long distance pollen flow, which is typical of forest trees, could slow down range shifts in the context of climate change but woud facilitate the evolution of new thermal tolrances and thus their persistance under future climates. Pollen flow increases the genetic diversity for key functional traits, and thus their adaptation capacity. Yet, demogenetic models that explicitly describe tree life cycles with a long juvenile period and high longevity of adults, predict very slow evolution despite abundant genetic variation.

Quanttication of selection pressures along climatic gradients and for different climate change scenarios is ongoing.

1. Duputié, A., Rutschmann, A., Ronce, O. & Chuine, I. (2015) Phenological plasticity will not help all species adapt to climate change. Global Change Biology.doi: 10.1111/gcb.12914 onlinelibrary.wiley.com/doi/10.1111/gcb.12914/abstract
2. Bonnefon O., Coville J., Garnier J., Hamel F. & Roques L. (2014) The spatio-temporal dynamics of neutral genetic diversity. Ecological Complexity, 20 282-292
3. K Csilléry*, H Lalagüe*, GG Vendramin, SC González-Martínez, B Fady and S Oddou-Muratorio 2014 Detecting local adaptation and epistatic selection in climate related candidate genes at a short spatial scale in European beech (Fagus sylvatica L.) populations. Molecular Ecology 23: 4696–4708
4. Dantec, C. F., Ducasse, H., Capdevielle, X., Fabreguettes, O., Delzon, S., & Desprez-Loustau, M. L. (2015). Escape of spring frost and disease through phenological variations in oak populations along elevation gradients. Journal of Ecology 103 , 1044-1056

Even if greenhouse gas emissions decrease in the next decades, rapid change in temperature and rainfall will occur, with long-term implications for the viability of ecosystems and their services. A major scientific challenge is thus to predict the adaptation of natural populations to this changing world in terms of migration, plasticity, and genetic change. Models predicting explicitly the impacts of climate change on biodiversity rarely incorporate any of these mechanisms of adaptation.

In this project, we aim at studying the interplay of the three above mechanisms to describe and forecast adaptation of forest trees to climate change. More specifically, we want to (1) evaluate the adaptive value of phenotypic plasticity in current and future climates at different spatial and temporal scales, (2) understand how microevolution in interaction with phenotypic plasticity and gene flow shape phenotypic variation, as well as predict how these three mechanisms of adaptation would act on phenotypic variation in the future, (3) use our increased understanding of phenotypic variation in time and space and its dynamics to better predict current and future species distribution under several scenarios of climate change.

Due to their life cycle characterized by long lifetime and large gene flow, forest trees are particularly exposed to temporal and spatial variation in selection. Plasticity may thus play a key role in forest trees response to climate change. The interplay between phenotypic plasticity, microevolution and gene flow on adaptation will be illustrated through the study of phenological traits in three forest tree species, beech, sessile oak and silver fir. Phenological traits have indeed been shown to be a major determinant of tree species distribution and ecosystem functioning. They also show strong responses to current climate change and large genetic variation both within and among populations, suggesting that they might evolve fast if climate change generates new selection pressures. We will focus on bud burst, taking advantage of well-adjusted process-based phenological models predicting its date of occurrence as a function of temperature and photoperiod.

The originality of our project lies in (i) integrating different adaptation mechanisms in ecological forecasts of climate change, which has only rarely been attempted; (ii) studying the interaction between these different mechanisms of adaptation, (iii) combining different types of modeling approaches and observations to both explore and predict the adaptive challenges and responses of tree populations experiencing climate changes. More precisely, we will make an original use of extant process-based models simulating variation in bud burst date and its impact on demographic rates, to quantitatively predict the direction and force of selection acting on phenological traits across environments in current and future climate. We will then incorporate this refined understanding of selection pressures in realistic ecological scenarios in quantitative genetics models of variable complexity to predict the joint changes in phenotypic and genetic values for bud burst dates. These predictions will be derived for a set of locations where the genetic and plastic variation in bud burst date are intensively studied, allowing quantitative tests of our predictions, as a validation step. To reach such objectives, our consortium gathers both modelers and experimentalists with complementary expertise in ecology, ecophysiology, quantitative genetics and evolutionary biology. The level of integration among the different tasks is very high. Results will (i) provide answers to fundamental questions about the evolution and adaptive value of phenotypic plasticity in variable environments, (ii) scenarios of range shift of forest tree species integrating adaptation processes and (iii) recommendations for forestry practices to manage the adaptive potential of forest tree species.