10 research outputs found

    Local differentiation in heat response of Laminaria digitata at the range edges

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    In recent years, kelp populations worldwide have faced decline and extirpation at their equatorward limits, while models predict a poleward shift of kelp ecosystems during climate change. To gain an understanding of local thermal adaptation and response plasticity in a forest-forming kelp species, we assessed populations of Laminaria digitata along its entire European distribution range for their capacity to withstand high temperature stress, and analysed population structure and diversity with microsatellite markers (n=12). We sampled wild meristematic L. digitata material (n=30) at six locations ranging from Kongsfjorden, Spitsbergen, to the southernmost distribution limit in Quiberon, France. In a heatwave experiment, we subjected samples from all locations to the same, sublethal temperature treatments (15–23°C for eight days including acclimation) and assessed growth, storage compounds, photosynthetic efficiency and pigment contents as response traits. Recovery was assessed following seven days at 15°C. Microsatellite genotyping revealed all sampled populations to be genetically distinct entities, underlying strong regional structuring between southern and northern clades. Genetic diversity was highest at the southern distribution limit in Quiberon and lowest in the geographically isolated population on the island of Helgoland in the North Sea. The physiological response of L. digitata to temperature was similar over the entire distribution range and did not reflect the mean temperature gradient along the latitudinal gradient. However, material from Spitsbergen and Helgoland presented subtle differentiations in their temperature responses, which reflect long-term local temperature histories at these sites. Finally, a heatwave reaching 23°C for five days led to a cessation of growth, from which none of the sampled populations recovered. Our results suggest that the heat stress response of L. digitata is generally stable across its distribution range, despite strong genetic structuring of the populations. Slight local differentiation occurred in populations from the most distinct thermal environments, but 23°C posed a growth limit for all populations. This implies that local adaptation in trailing edge populations of L. digitata might not alleviate detrimental effects of global warming

    Adaptation dans les populations centrales et marginales : contribution de la sélection, de la connectivité et du système de reproduction. Approche théorique et empirique sur l'espèce d'algue brune Laminaria digitata

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    I first investigated the historical factors that may explain the distribution of genetic diversity across the distributional range of the kelp Laminaria digitata. This study was combined with studies on spatio-temporal variation of populations, connectivity studies at the scale of the French coasts and an exploration of local adaptation in the face of temperature by the means of a common garden experiment. In addition to marginal populations, I investigated the fate of isolated populations, located in the center of the species' distribution range, but isolated from gene flows by different barriers to dispersal. In a second part of my thesis, I used theoretical approaches to understand the emergence of geographical parthenogenesis, corresponding to an evolution towards an asexual mode of reproduction at the range limits. In particular, I studied the validity of two hypotheses based on different characteristics of marginal populations. The first assumes that asexual reproduction is beneficial as it allows the maintenance of phenotypes adapted to extreme environmental conditions in the face of an influx of maladapted migrants, and was studied using a model in which a quantitative trait evolves along an environmental gradient. The second assumes that asexual reproduction avoids inbreeding depression resulting from reproduction between related individuals in a structured population. This hypothesis was studied using an infinite island model, in which diploid individuals are characterized by a locus under selection and a locus affecting their mode of reproduction.Je me suis d'abord intéressée aux facteurs historiques pouvant expliquer la répartition de la diversité génétique à travers l'aire de distribution de Laminaria digitata. Cette étude a été combinée avec des études de la variation spatio-temporelle des populations ; de connectivité à l'échelle des côtes françaises et d'une exploration du phénomène d'adaptation locale à la température au moyen d'une expérience en jardin commun. Outre les populations marginales, je me suis également intéressé au devenir de populations isolées, c'est-à-dire situées au centre de l'aire de distribution mais isolées des flux de gènes par différentes barrières à la dispersion. Dans un deuxième volet de ma thèse, j'ai utilisé des approches théoriques pour comprendre l'émergence de la parthénogenèse géographique, correspondant à une évolution vers un mode de reproduction asexué en limite d'aire. J’ai étudié la validité de deux hypothèses reposant sur différentes caractéristiques des populations marginales. La première suppose que la reproduction asexuée permet de maintenir l'adaptation à des conditions environnementales extrêmes face à un afflux de migrants mal adaptés, et a été étudiée à l'aide d'un modèle d'évolution d'un trait quantitatif le long d'un gradient environnemental dans lequel les individus sont haploïdes. La deuxième suppose que la reproduction asexuée permet d'éviter la dépression de consanguinité résultant des croisements entre individus apparentés en population structurée. Cette hypothèse a été étudiée à l'aide d'un modèle en îles infini, dans lequel les individus diploïdes sont caractérisés par un locus sous sélection et un locus affectant leur mode de reproduction

    Adaptation in central and marginal populations : contribution of selection, connectivity and reproductive systems. Theoretical and empirical approaches on the kelp Laminaria digitata.

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    Je me suis d'abord intéressée aux facteurs historiques pouvant expliquer la répartition de la diversité génétique à travers l'aire de distribution de Laminaria digitata. Cette étude a été combinée avec des études de la variation spatio-temporelle des populations ; de connectivité à l'échelle des côtes françaises et d'une exploration du phénomène d'adaptation locale à la température au moyen d'une expérience en jardin commun. Outre les populations marginales, je me suis également intéressé au devenir de populations isolées, c'est-à-dire situées au centre de l'aire de distribution mais isolées des flux de gènes par différentes barrières à la dispersion. Dans un deuxième volet de ma thèse, j'ai utilisé des approches théoriques pour comprendre l'émergence de la parthénogenèse géographique, correspondant à une évolution vers un mode de reproduction asexué en limite d'aire. J’ai étudié la validité de deux hypothèses reposant sur différentes caractéristiques des populations marginales. La première suppose que la reproduction asexuée permet de maintenir l'adaptation à des conditions environnementales extrêmes face à un afflux de migrants mal adaptés, et a été étudiée à l'aide d'un modèle d'évolution d'un trait quantitatif le long d'un gradient environnemental dans lequel les individus sont haploïdes. La deuxième suppose que la reproduction asexuée permet d'éviter la dépression de consanguinité résultant des croisements entre individus apparentés en population structurée. Cette hypothèse a été étudiée à l'aide d'un modèle en îles infini, dans lequel les individus diploïdes sont caractérisés par un locus sous sélection et un locus affectant leur mode de reproduction.I first investigated the historical factors that may explain the distribution of genetic diversity across the distributional range of the kelp Laminaria digitata. This study was combined with studies on spatio-temporal variation of populations, connectivity studies at the scale of the French coasts and an exploration of local adaptation in the face of temperature by the means of a common garden experiment. In addition to marginal populations, I investigated the fate of isolated populations, located in the center of the species' distribution range, but isolated from gene flows by different barriers to dispersal. In a second part of my thesis, I used theoretical approaches to understand the emergence of geographical parthenogenesis, corresponding to an evolution towards an asexual mode of reproduction at the range limits. In particular, I studied the validity of two hypotheses based on different characteristics of marginal populations. The first assumes that asexual reproduction is beneficial as it allows the maintenance of phenotypes adapted to extreme environmental conditions in the face of an influx of maladapted migrants, and was studied using a model in which a quantitative trait evolves along an environmental gradient. The second assumes that asexual reproduction avoids inbreeding depression resulting from reproduction between related individuals in a structured population. This hypothesis was studied using an infinite island model, in which diploid individuals are characterized by a locus under selection and a locus affecting their mode of reproduction

    Temporal genomics help in deciphering neutral and adaptive patterns in the contemporary evolution of kelp populations

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    International audienceThe impact of climate change on populations will be contingent upon their contemporary adaptive evolution. In this study, we investigated the contemporary evolution of four populations of the cold-water kelp Laminaria digitata by analysing their spatial and temporal genomic variation using ddRAD-sequencing. These populations were sampled from the center to the southern margin of its north-eastern Atlantic distribution at two-time points, spanning at least two generations. Through genome scans for local adaptation at a single time point, we identified candidate loci that showed clinal variation correlated with changes in sea surface temperature (SST) along latitudinal gradients. This finding suggests that SST may drive the adaptive response of these kelp populations, although factors such as species' demographic history should also be considered. Additionally, we performed a simulation approach to distinguish the effect of selection from genetic drift in allele frequency changes over time. This enabled the detection of loci in the southernmost population that exhibited temporal differentiation beyond what would be expected from genetic drift alone: these are candidate loci which could have evolved under selection over time. In contrast, we did not detect any outlier locus based on temporal differentiation in the population from the North Sea, which also displayed low and decreasing levels of genetic diversity. The diverse evolutionary scenarios observed among populations can be attributed to variations in the prevalence of selection relative to genetic drift across different environments. Therefore, our study highlights the potential of temporal genomics to offer valuable insights into the contemporary evolution of marine foundation species facing climate change

    Temporal genomics help in deciphering neutral and adaptive patterns in the contemporary evolution of kelp populations

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    ABSTRACT The long-term persistence of species in the face of climate change can be evaluated by examining the interplay between selection and genetic drift in the contemporary evolution of populations. In this study, we focused on spatial and temporal genetic variation in four populations of the cold-water kelp Laminaria digitata using thousands of SNPs (ddRAD-seq). These populations were sampled from the center to the south margin in the North Atlantic at two different time points, spanning at least two generations. By conducting genome scans for local adaptation from a single time point, we successfully identified candidate loci that exhibited clinal variation, closely aligned with the latitudinal changes in temperature. This finding suggests that temperature may drive the adaptive response of kelp populations, although other factors, such as the species’ demographic history should be considered. Furthermore, we provided compelling evidence of positive selection through the examination of allele frequency changes over time, offering additional insights into the impact of genetic drift. Specifically, we detected candidate loci exhibiting temporal differentiation that surpassed the levels typically attributed to genetic drift at the south margin, confirmed through simulations. This finding was in sharp contrast with the lack of detection of outlier loci based on temporal differentiation in a population from the North Sea, exhibiting low levels of genetic diversity, that further decreased over time. These contrasting evolutionary scenarios among populations can be primarily attributed to the differential prevalence of selection relative to genetic drift. In conclusion, our study highlights the potential of temporal genomics to gain deeper insights into the contemporary evolution of marine foundation species in response to rapid environmental changes

    Data from: Nonlinear phenotypic variation uncovers the emergence of heterosis in Arabidopsis thaliana

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    Heterosis describes the phenotypic superiority of hybrids over their parents in traits related to agronomic performance and fitness. Understanding and predicting nonadditive inheritance such as heterosis is crucial for evolutionary biology as well as for plant and animal breeding. However, the physiological bases of heterosis remain debated. Moreover, empirical data in various species have shown that diverse genetic and molecular mechanisms are likely to explain heterosis, making it difficult to predict its emergence and amplitude from parental genotypes alone. In this study, we examined a model of physiological dominance initially proposed by Sewall Wright to explain the nonadditive inheritance of traits like metabolic fluxes at the cellular level. We evaluated Wright’s model for two fitness-related traits at the whole-plant level, growth rate and fruit number, using 450 hybrids derived from crosses among natural accessions of A. thaliana. We found that allometric relationships between traits constrain phenotypic variation in a nonlinear and similar manner in hybrids and accessions. These allometric relationships behave predictably, explaining up to 75% of heterosis amplitude, while genetic distance among parents at best explains 7%. Thus, our findings are consistent with Wright’s model of physiological dominance and suggest that the emergence of heterosis on plant performance is an intrinsic property of nonlinear relationships between traits. Furthermore, our study highlights the potential of a geometric approach of phenotypic relationships for predicting heterosis of major components of crop productivity and yield

    S1_Data

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    This file contains trait values measured (1) on accessions and hybrid individuals of Arabidopsis thaliana, as well as (2) on a set of 334 plant species obtained from the study of Niklas and Enquist (PNAS 2001; 98: 2922-2927). These data are used in the article entitled Non-linear phenotypic variation uncovers the emergence of heterosis in Arabidopsis thaliana, published in 2019 by Vasseur and colleagues in PLOS Biology. For A. thaliana data, traits were measured with the same protocol in two experiments that took place at the Max Planck Institute for Development Biology (Tübingen, Germany) between 2013 and 2015. idExp represents experiment identifier: GT01, which is the first experiment and which contains 451 accessions (n=2), and GT05, the second experiment which contains 450 hybrids (n=4) and 16 accessions (n=4). The GT01 experiment has also been described and analyzed by Vasseur and colleagues. (PNAS 2018; 115: 3416-3421). Identifier numbers are 1001 Genomes identifiers (http://1001genomes.org/). Detailed protocol for trait measurement can be found in Image-based methods for phenotyping growth dynamics and fitness in Arabidopsis thaliana (Vasseur et al., Plant Methods 2018; 14: 63; https://doi.org/10.1101/208512). Units of traits measured: Age at reproduction: duration in days between the emergence of the first two leaves and the end of reproduction, when fruits are drying. FruitNumber: total number of fruits (siliques) per individual, measured at the end of reproduction. GrowthRate: Average growth rate (mg d-1), measured as the ratio of final rosette dry mass over age at reproduction. VegetativeDryMass: rosette dry mass (mg) measured at the growth inflection point (when growth rate is maximum), which was estimated by fitting a sigmoid growth curve on plant dry mass over time

    Nonlinear phenotypic variation uncovers the emergence of heterosis in Arabidopsis thaliana

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    Heterosis describes the phenotypic superiority of hybrids over their parents in traits related to agronomic performance and fitness. Understanding and predicting nonadditive inheritance such as heterosis is crucial for evolutionary biology as well as for plant and animal breeding. However, the physiological bases of heterosis remain debated. Moreover, empirical data in various species have shown that diverse genetic and molecular mechanisms are likely to explain heterosis, making it difficult to predict its emergence and amplitude from parental genotypes alone. In this study, we examined a model of physiological dominance initially proposed by Sewall Wright to explain the nonadditive inheritance of traits like metabolic fluxes at the cellular level. We evaluated Wright's model for two fitness-related traits at the whole-plant level, growth rate and fruit number, using 450 hybrids derived from crosses among natural accessions of A. thaliana. We found that allometric relationships between traits constrain phenotypic variation in a nonlinear and similar manner in hybrids and accessions. These allometric relationships behave predictably, explaining up to 75% of heterosis amplitude, while genetic distance among parents at best explains 7%. Thus, our findings are consistent with Wright's model of physiological dominance and suggest that the emergence of heterosis on plant performance is an intrinsic property of nonlinear relationships between traits. Furthermore, our study highlights the potential of a geometric approach of phenotypic relationships for predicting heterosis of major components of crop productivity and yield

    Desenvolvimento de ferramentas para identificar rapidamente espécies enigmáticas e caracterizar sua diversidade genética em diferentes espécies Europeias de algas

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    Marine ecosystems formed by kelp forests are severely threatened by global change and local coastline disturbances in many regions. In order to take appropriate conservation, mitigation, and restoration actions, it is crucial to identify the most diverse populations which could serve as a “reservoir” of genetic diversity. This requires the development of specifc tools, such as microsatellite markers to investigate the level and spatial distribution of genetic diversity. Here, we tested new polymorphic microsatellite loci from the genome of the kelp, Laminaria digitata, and tested them for cross-amplifcation and polymorphism in four closely related congeneric species (Laminaria hyperborea, Laminaria ochroleuca, Laminaria rodriguezii, and Laminaria pallida). Adding these 20 new microsatellite loci to the ten L. digitata loci previously developed by Billot et al. (Mol Ecol 7:1778-1780, 1998) and Brenan et al. (J R Soc Interface 11:1-12, 2014) and to the ten L. ochroleuca loci previ ously developed by Coelho et al. (Conserv Genet Resource 6:949-950, 2014), we retained a total of 30 polymorphic loci for L. digitata, 21 for L. hyperborea, 16 for L ochroleuca, 18 for L. rodriguezii, and 12 for L. pallida. These markers have been tested for the frst time in the last two species. As predicted, the proportion of markers that cross-amplifed between species decreased with increasing genetic distance. In addition, as problems of species identifcation were reported in this family, mainly between L. digitata and Hedophyllum nigripes, but also between L. digitata, L. hyperborea, and L. ochroleuca in areas where their range distributions overlap, we report a rapid PCR identifcation method based on species-specifc COI mitochondrial primers that allows these four species of kelp to be rapidly distinguished.info:eu-repo/semantics/publishedVersio

    Genetic structure of amphi-Atlantic Laminaria digitata (Laminariales, Phaeophyceae) reveals a unique range-edge gene pool and suggests post-glacial colonization of the NW Atlantic

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    In the North-east (NE) Atlantic, most intertidal fucoids and warm-temperate kelps show unique low-latitude gene pools matching long-term climatic refugia. For cold-temperate kelps data are scarcer despite their unique cultural, ecological and economic significance. Here we test whether the amphi-Atlantic range of Laminaria digitata is derived from past glacial survival (and vicariance) in both NE and North-west (NW) Atlantic refugia (as suggested by niche modelling), or post-glacial (re)colonization (as suggested by low mtDNA divergence). We screened 14 populations from across the species range for 12 microsatellite loci to identify and map major gene pools and refugia. We assessed if NW Atlantic survival was supported by unique endemic variation, and if genetic diversity and structure were, as predicted from larger hindcasted glacial ranges, higher in the NE Atlantic. Microsatellite data subdivided L. digitata into three main genetic groups matching Brittany, northern Europe and the NW Atlantic, with finer-scale sub-structuring within European clusters. The relatively diverse NE Atlantic lineages probably survived the Last Glacial Maximum along unglaciated periglacial shorelines of the Armorican and Celtic Seas (Brittany cluster) and Ireland (northern European cluster), and remain well differentiated despite their relative proximity. The unique Brittany gene pool, at the contemporary European rear edge, is projected to disappear in the near future under high greenhouse gas emission scenarios. Low allelic diversity and low endemism in the NW Atlantic are consistent with recent post-glacial colonization from Europe, challenging the long-standing hypothesis of in situ glacial survival. Confusion with Hedophyllum nigripes may have led to underestimation of regional diversity of L. digitata, but also to overestimation of its presence along putative trans-Atlantic migration routes. Partial incongruence between modelling and genetic-based biogeographic inferences highlights the benefits of comparing both approaches to understand how shifting climatic conditions affect marine species distributions and explain large-scale patterns of spatial genetic structure.PTDC/MAR-EST/6053/2014, Biodiversa/0004/2015, UID/Multi/04326/2019, SFRH/BSAB/150485/2019 (to EAS) and Norma Transitória DL 57/2016/CP1361/CT001info:eu-repo/semantics/publishedVersio
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