In situ Comparison of Tree-Ring Responses to Climate and Population Genetics: The Need to Control for Local Climate and Site Variables

Tree species responses to climate change will be greatly influenced by their evolutionary potential and their phenotypic plasticity. Investigating tree-rings responses to climate and population genetics at the regional scale is crucial in assessing the tree behavior to climate change. This study combined in situ dendroclimatology and population genetics over a latitudinal gradient and compared the variations between the two at the intra- and inter-population levels. This approach was applied on the northern marginal populations of Thuja occidentalis (eastern white-cedar) in the Canadian boreal forest. We aimed first to assess the radial growth variability (response functional trait) within populations across the gradient and to compare it with the genetic diversity (microsatellites). Second, we investigated the variability in the growth response to climate at the regional scale through the radial growth-climate relationships, and tested its correlation with environmental variables and population genetic structure. Model selection based on the Akaike Information Criteria revealed that the growth synchronicity between pairs of trees of a population covariates with both the genetic diversity of this population and the amount of precipitation (inverse correlations), although these variables only explained a small fraction of the observed variance. At the regional scale, variance partitioning and partial redundancy analysis indicate that the growth response to climate was greatly modulated by stand environmental variables, suggesting predominant plastic variations in growth-response to climate. Combining in situ dendroclimatology and population genetics is a promising way to investigate species' response capacity to climate change in natural stands. We stress the need to control for local climate and site conditions effects on dendroclimatic response to climate to avoid misleading conclusions regarding the associations with genetic variables

Variations de croissance et capacité d’adaptation des populations marginales fragmentées d’arbres des zones boréo-montagnardes, en réponse aux changements climatiques

This thesis aims to assess the fate of marginal populations, in the context of climate change, for boreo-mountain tree species. The dendroclimatic response and the genetic structure of the species are jointly analyzed on gradients including both the continuous and the marginal distribution zones. Two biological models have been chosen for this research, white cedar at its northern limit (boreal forest) and stone pine at its western limit (temperate mountain forest). The following hypotheses were tested: global warming during the twentieth century has led to increased growth; growth variability is related to the genetic structure at the intra- and inter-population levels. A decline in cedar growth was observed after 1980 in marginal zone, which could be linked to drought constraints on growth. For both species, climate-growth relationships were essentially modulated by the amount of precipitation, but also by soil and tree-size variables. The existence of a significant link between genetic structure and some climatic variables still leaves some hope for a genetic adaptation potential, which magnitude will depend on the genetic diversity available for natural selection. The growth synchronicity between the trees was both influenced by the intra-population genetic diversity and the amount of precipitation. In conclusion, it is very difficult to disentangle the effects of climate and genetics on the growth of the studied trees.Cette thèse a pour objectif de déterminer le devenir des populations marginales d’arbres boréo-montagnards dans le contexte des changements climatiques. La réponse dendroclimatique et la structure génétique des espèces sont analysées conjointement sur des gradients incluant les zones de distributions continues et marginales. Les deux modèles biologiques choisis sont le thuya occidental en limite nordique (forêt boréale canadienne) et le pin cembro en limite occidentale (Alpes). Les hypothèses suivantes ont été testées : le réchauffement climatique au cours du XXe siècle a entrainé une augmentation de croissance ; la variabilité de croissance est reliée à la structure génétique aux niveaux intra- et inter-populationnels. Une baisse de croissance du thuya a été observée après 1980 en zone marginale, qui serait liée à une limitation par la sécheresse. Pour les deux espèces, les relations climat-croissance étaient essentiellement modulées par le volume des précipitations, mais également par des variables édaphiques et par la taille des arbres. L’existence d’un lien significatif entre la structure génétique et certaines variables climatiques laisse néanmoins espérer un potentiel d'adaptation génétique, dont l’ampleur dépendra de la diversité génétique disponible pour la sélection naturelle. Par ailleurs, le synchronisme de croissance entre les arbres était à la fois influencé par la diversité génétique intra-populationnelle et par le volume des précipitations. En conclusion, il apparaît très difficile de distinguer les effets du climat et de la génétique sur la croissance des arbres étudiés

Growth variations and adaptation capacity of fragmented marginal tree populations in boreo-mountain zones, in response to climate change

Cette thèse a pour objectif de déterminer le devenir des populations marginales d’arbres boréo-montagnards dans le contexte des changements climatiques. La réponse dendroclimatique et la structure génétique des espèces sont analysées conjointement sur des gradients incluant les zones de distributions continues et marginales. Les deux modèles biologiques choisis sont le thuya occidental en limite nordique (forêt boréale canadienne) et le pin cembro en limite occidentale (Alpes). Les hypothèses suivantes ont été testées : le réchauffement climatique au cours du XXe siècle a entrainé une augmentation de croissance ; la variabilité de croissance est reliée à la structure génétique aux niveaux intra- et inter-populationnels. Une baisse de croissance du thuya a été observée après 1980 en zone marginale, qui serait liée à une limitation par la sécheresse. Pour les deux espèces, les relations climat-croissance étaient essentiellement modulées par le volume des précipitations, mais également par des variables édaphiques et par la taille des arbres. L’existence d’un lien significatif entre la structure génétique et certaines variables climatiques laisse néanmoins espérer un potentiel d'adaptation génétique, dont l’ampleur dépendra de la diversité génétique disponible pour la sélection naturelle. Par ailleurs, le synchronisme de croissance entre les arbres était à la fois influencé par la diversité génétique intra-populationnelle et par le volume des précipitations. En conclusion, il apparaît très difficile de distinguer les effets du climat et de la génétique sur la croissance des arbres étudiés.This thesis aims to assess the fate of marginal populations, in the context of climate change, for boreo-mountain tree species. The dendroclimatic response and the genetic structure of the species are jointly analyzed on gradients including both the continuous and the marginal distribution zones. Two biological models have been chosen for this research, white cedar at its northern limit (boreal forest) and stone pine at its western limit (temperate mountain forest). The following hypotheses were tested: global warming during the twentieth century has led to increased growth; growth variability is related to the genetic structure at the intra- and inter-population levels. A decline in cedar growth was observed after 1980 in marginal zone, which could be linked to drought constraints on growth. For both species, climate-growth relationships were essentially modulated by the amount of precipitation, but also by soil and tree-size variables. The existence of a significant link between genetic structure and some climatic variables still leaves some hope for a genetic adaptation potential, which magnitude will depend on the genetic diversity available for natural selection. The growth synchronicity between the trees was both influenced by the intra-population genetic diversity and the amount of precipitation. In conclusion, it is very difficult to disentangle the effects of climate and genetics on the growth of the studied trees

IN SITU COMPARISON OF TREE-RING RESPONSES TO CLIMATE AND POPULATION GENETICS: THE NEED TO CONTROL FOR LOCAL CLIMATE AND SITE VARIABLES

Tree species responses to climate change will be greatly influenced by their evolutionary potential and their phenotypic plasticity. Investigating tree-rings responses to climate and population genetics at the regional scale is therefore crucial in assessing the tree behaviour to climate change. This study combined in situ dendroclimatology and population genetics over a latitudinal gradient and compared the variations between the two at the intra- and inter-population levels. This approach was applied on the northern marginal populations of Thuja occidentalis (eastern white-cedar) in the Canadian boreal forest. We aimed first to assess the radial growth variability (response functional trait) within populations across the gradient and to compare it with the genetic diversity (microsatellites). Second, we investigated the variability in the growth response to climate at the regional scale through the radial growth-climate relationships, and tested its correlation with environmental variables and population genetic structure. Model selection based on the Akaike Information Criteria revealed that the growth synchronicity between pairs of trees of a population covariates with both the genetic diversity of this population and the amount of precipitation (inverse correlation), although these variables only explained a small fraction of the observed variance. At the regional scale, variance partitioning and partial redundancy analysis indicate that the growth response to climate was greatly modulated by stand environmental variables, suggesting predominant plastic variations in growth-response to climate. Combining in situ dendroclimatology and population genetics is a promising way to investigate species’ response capacity to climate change in natural stands. We stress the need to control for local climate and site conditions effects on dendroclimatic response to climate to avoid misleading conclusions regarding the associations with genetic variables

Geographic isolation and climatic variability contribute to genetic differentiation in fragmented populations of the long-lived subalpine conifer Pinus cembra L. in the western Alps

International audienc

Tree-rings, genetics and the environment: Complex interactions at the rear edge of species distribution range

International audienceUnder climate change, modifications on plants’ growth are expected to be the strongest at species margins. Therein, tree acclimation could play a key role as migration is predicted to be too slow to track shifts of bioclimatic envelops. A requirement is, however, that intra-population genetic diversity be high enough for allowing such adaptation of tree populations to climate change. In this study, we tested for the existence of relationships between genetic diversity, site environmental conditions, and the response of annual tree growth to climate of Pinus cembra at its southern limit in the Alps. Site-specific climatic and environmental factors pre- dominantly determined the response of trees along the precipitation gradient. The growth-climate interactions were chiefly linked to mean annual precipitation and temperature, slope and tree-size, and less to genetic di- versity. We show that genetic background of Pinus cembra has exclusively indirect modulating power with limited effects on tree-ring formation, and within the southern limit in the Alps, genetic variability is not necessarily well expressed in the patterns of annual tree growth. Our results may imply little adaptive capacity of these pop- ulations to future changes in the water balance

Carex guyana SNP dataset, Andean wetland plant community dataset, and environmental data for species genetic diversity correlation study

This data folder includes the five filtered SNP datasets for the plant species, Carex guyana, a common sedge in high elevation Andes wetlands (final_partitioned_SNPdatasets). Details regading the partitioned neutral and adaptive datasets can be found in the accompanying Ecology and Evolution 2018 paper. The folder also contains the plant community datasets (DatosPlantsCommunity_modified) used to contrast plant species and Carex guyana genetic diversity in the species genetic diversity correlation study, as well as the environmental data (EnvData)

Data from: Partitioning genetic and species diversity refines our understanding of species-genetic diversity relationships

Illuminating the origin of species-genetic diversity correlations (SGDCs) is a challenging task that has sparked a lot of interest. Genetic and species diversity are comprised by components that respond differently to the same ecological processes. Thus, it can be useful to partition species and genetic diversity into their different components to infer the mechanisms behind SGDCs. In this study, we applied such an approach using a high-elevation Andean wetland system, where previous evidence identified neutral processes as major determinants of the strong and positive covariation between plant species richness and AFLP genetic diversity of the common sedge Carex gayana. To tease apart putative neutral and non-neutral genetic variation of C. gayana, we identified loci putatively under selection from a dataset of 1709 SNPs produced using restriction site-associated DNA sequencing (RAD-seq). Significant and positive relationships between local estimates of genetic and species diversities (α-SGDCs) were only found with the putatively neutral loci datasets and with species richness, confirming that neutral processes were primarily driving the correlations and that the involved processes differentially influenced local species diversity components (i.e. richness and evenness). In contrast, SGDCs based on genetic and community dissimilarities (-SGDCs) were only significant with the putative non-neutral datasets. This suggests that selective processes influencing C. gayana genetic diversity were involved in the detected correlations. Together, our results demonstrate that analyzing distinct components of genetic and species diversity simultaneously is useful to determine the mechanisms behind species-genetic diversity relationships

Data from: Partitioning genetic and species diversity refines our understanding of species-genetic diversity relationships

Illuminating the origin of species-genetic diversity correlations (SGDCs) is a challenging task that has sparked a lot of interest. Genetic and species diversity are comprised by components that respond differently to the same ecological processes. Thus, it can be useful to partition species and genetic diversity into their different components to infer the mechanisms behind SGDCs. In this study, we applied such an approach using a high-elevation Andean wetland system, where previous evidence identified neutral processes as major determinants of the strong and positive covariation between plant species richness and AFLP genetic diversity of the common sedge Carex gayana. To tease apart putative neutral and non-neutral genetic variation of C. gayana, we identified loci putatively under selection from a dataset of 1709 SNPs produced using restriction site-associated DNA sequencing (RAD-seq). Significant and positive relationships between local estimates of genetic and species diversities (α-SGDCs) were only found with the putatively neutral loci datasets and with species richness, confirming that neutral processes were primarily driving the correlations and that the involved processes differentially influenced local species diversity components (i.e. richness and evenness). In contrast, SGDCs based on genetic and community dissimilarities (-SGDCs) were only significant with the putative non-neutral datasets. This suggests that selective processes influencing C. gayana genetic diversity were involved in the detected correlations. Together, our results demonstrate that analyzing distinct components of genetic and species diversity simultaneously is useful to determine the mechanisms behind species-genetic diversity relationships