Where is the optimum? Predicting the variation of selection along climatic gradients and the adaptive value of plasticity. A case study on tree phenology

International audienceMany theoretical models predict when genetic evolution and phenotypic plasticity allow adaptation to changing environmental conditions. These models generally assume stabilizing selection around some optimal phenotype. We however often ignore how optimal phenotypes change with the environment, which limit our understanding of the adaptive value of phenotypic plasticity. Here, we propose an approach based on our knowledge of the causal relationships between climate, adaptive traits, and fitness to further these questions. This approach relies on a sensitivity analysis of the process-based model Phenofit, which mathematically formalizes these causal relationships, to predict fitness landscapes and optimal budburst dates along elevation gradients in three major European tree species. Variation in the overall shape of the fitness landscape and resulting directional selection gradients were found to be mainly driven by temperature variation. The optimal budburst date was delayed with elevation, while the range of dates allowing high fitness narrowed and the maximal fitness at the optimum decreased. We also found that the plasticity of the budburst date should allow tracking the spatial variation in the optimal date, but with variable mismatch depending on the species, ranging from negligible mismatch in fir, moderate in beech, to large in oak. Phenotypic plasticity would therefore be more adaptive in fir and beech than in oak. In all species, we predicted stronger directional selection for earlier budburst date at higher elevation. The weak selection on budburst date in fir should result in the evolution of negligible genetic divergence, while beech and oak would evolve counter-gradient variation, where genetic and environmental effects are in opposite directions. Our study suggests that theoretical models should consider how whole fitness landscapes change with the environment. The approach introduced here has the potential to be developed for other traits and species to explore how populations will adapt to climate change

Darwin’s wind hypothesis: does it work for plant dispersal in fragmented habitats?

Using the wind-dispersed plant Mycelis muralis, we examined how landscape fragmentation affects variation in seed traits contributing to dispersal. Inverse terminal velocity (Vt−1) of field-collected achenes was used as a proxy for individual seed dispersal ability. We related this measure to different metrics of landscape connectivity, at two spatial scales: in a detailed analysis of eight landscapes in Spain and along a latitudinal gradient using 29 landscapes across three European regions. In the highly patchy Spanish landscapes, seed Vt−1 increased significantly with increasing connectivity. A common garden experiment suggested that differences in Vt−1 may be in part genetically based. The Vt−1 was also found to increase with landscape occupancy, a coarser measure of connectivity, on a much broader (European) scale. Finally, Vt−1 was found to increase along a south–north latitudinal gradient. Our results for M. muralis are consistent with ‘Darwin’s wind dispersal hypothesis’ that high cost of dispersal may select for lower dispersal ability in fragmented landscapes, as well as with the ‘leading edge hypothesis’ that most recently colonized populations harbour more dispersive phenotypes.

How does it feel to be like a rolling stone? Ten questions about dispersal evolution

ReviewInternational audienceThis review proposes ten tentative answers to frequently asked questions about dispersal evolution. I examine methodological issues, model assumptions and predictions, and their relation to empirical data. Study of dispersal evolution points to the many ecological and genetic feedbacks affecting the evolution of this complex trait, which has contributed to our better understanding of life-history evolution in spatially structured populations. Several lines of research are suggested to ameliorate the exchanges between theoretical and empirical studies of dispersal evolution

Ophélie Ronce : "Amb els models predictius millorarem el coneixement fenològic, però mai no podrem integrar tota la complexitat de les interaccions entre espècies"

En motiu de la seva visita al CREAF dins el programa CREAFTalks, entrevistem ala investigadora Ophélie Ronce, directora del grup de recerca CNRS de la Universitat de Montpellier i membre del Consell científic del CREAF des del 2017. L'Ophélie estudia el paper de l'evolució quant a resposta de la biodiversitat als canvis globals mitjançant models matemàtics.Con motivo de su visita al CREAF dentro del programa CREAFTalks, entrevistamos a la investigadora Ophélie Ronce, directora del grupo de investigación CNRS de la Universidad de Montpellier. Ophélie estudia el papel de la evolución en la respuesta de la biodiversidad a los cambios globales mediante modelos matemáticos.On the occasion of her visit to CREAF as part of the CREAFTalks program, we interviewed researcher Ophélie Ronce, director of the CNRS research group at the University of Montpellier and member of the CREAF Scientific Council since 2017. Ophélie studies the role of evolution in biodiversity response to global changes through mathematical models

Understanding plant dispersal and migration

Research updateInternational audienc

Phenotypic plasticity for dispersal ability in the seed heteromorphic Crepis sancta (Asteraceae)

International audienceIn several species of Asteraceae with seed heteromorphism, the proportion of seeds equipped with wind-dispersal structure decreases plastically under stressful conditions. This contradicts the adaptive expectation that the dispersal rate should increase with stress. Alternatively, developmental constraints related to the ontogeny of the capitulum may explain these observations, as they may explain the effect of senescence on seed morph proportions. In the present paper, we report on an experiment investigating the effect of stress and senescence on the seed heteromorphic Crepis sancta (Asteraceae). Plants were subjected to one of four different treatments: control, simulated herbivory, nutrient depletion, and simulated herbivory plus nutrient depletion. Plants experiencing herbivory produced more fecund seed heads immediately after the application of stress, which was later compensated by a decrease in fecundity per seed head. Environmental stress increased the proportion of seeds with dispersal structures. Though senescence had large effects on fecundity, it had no effect on seed morph proportions in nonstressed plants. These findings agree with adaptive expectations about the effect of stress on dispersal ability, and contrast with results obtained in other seed heteromorphic Asteraceae. Our results cast doubts on the existence of strong developmental constraints acting on the seed morph proportions in Crepis sancta

Inclusive fitness for traits affecting metapopulation demography

International audienceDefining computable analytical measures of the effects of selection in populations with demographic and environmental stochasticity is a long-standing problem. We derive an analytical measure which takes in account all consequences of the discrete nature of deme size. Expressions of this measure are detailed for infinite island models of population structure. As an illustration we consider the evolution of dispersal in populations made of small demes with environmental and demographic stochasticity. We confirm some results obtained from the analysis of models based on deterministic approximations. In particular, when there is an Allee effect, we show that evolution of the dispersal rate may lead the metapopulation to extinction. Thus, selection on the dispersal rate could restrict the distribution of species subject to Allee effects. This selection-driven extinction is prevented by kin selection when the environmental extinction rate is small

Evolution of reproductive effort in a metapopulation with local extinctions and ecological succession

International audienceUsing a metapopulation model, we study how local extinctions, limited population life span, and local demographic disequilibrium affect the evolution of the reproductive effort in a species with overlapping generations but no senescence. We show that in a metapopulation with saturation of all sites and an infinite deme maximal life span (no succession), local extinctions simply constitute an additional source of extrinsic mortality. When either the hypothesis of an infinite deme maximal life span or the saturation hypothesis is relaxed, nontrivial predictions arise. In particular, we find interactions between the evolutionarily stable reproductive effort strategy and the demographic dynamics in the metapopulation. We predict that larger reproductive effort may be selected for in habitats of poorer productivity, contrary to what would be predicted in a single population. Also, we predict that higher dispersal rates should favor selection for lower reproductive efforts. However, metapopulation parameters that favor high dispersal rates also favor larger reproductive efforts. Conflicting selection pressures in the metapopulation also allow maintaining evolutionarily stable polymorphism between a low and high reproductive effort for particular trade-offs between survival and fecundity