Altruisme avec reconnaissance et mélanges variétaux

Maste

Prediction of extinction in plants: interaction of extrinsic threats and life history traits

The global extinction of species proceeds through the erosion of local populations. Using a 60- year time series of annual sighting records of plant species, we studied the correlates of local extinction risk associated with a risk of species extinction in the Park Grass Experiment where plants received long- term exposure to nutrient enrichment, soil acidification, and reductions in habitat size. We used multivariate linear models to assess how extrinsic threats and life history traits influence extinction risk. We investigated effects of four extrinsic threats ( nitrogen enrichment, productivity, acidification, and plot size) as well as 11 life history traits ( month of earliest. flowering,. flowering duration, stress tolerance, ruderalness plant species' ability to cope with habitat disturbance], plant height, diaspore mass, seed bank, life form, dispersal mode, apomixis the ability for a species to reproduce asexually through seeds], and mating system). Extinction risk was not influenced by plant family. All of the 11 life history traits except life form and all threat variables influenced extinction risk but always via interactions which typically involved one threat variable and one life history trait. We detected comparatively few significant interactions between life history traits, and the interacting traits compensated for each other. These results suggest that simple predictions about extinction risk based on species' traits alone will often fail. In contrast, understanding the interactions between extrinsic threats and life history traits will allow us to make more accurate predictions of extinctions

Analysis of the Transport of Aerosols over the North Tropical Atlantic Ocean Using Time Series of POLDER/PARASOL Satellite Data

International audienceThe time series of total, fine and coarse POLAC/PARASOL aerosol optical depth (AOD) satellite products (2005–2013) processed by the POLAC algorithm are examined to investigate the transport of aerosols over the North Tropical Atlantic Ocean, a region that is characterized by significant dust aerosols events. First, the comparison of satellite observations with ground-based measurements acquired by AERONET ground-based measurements shows a satisfactory consistency for both total AOD and coarse mode AOD (i.e., correlation coefficients of 0.75 and bias ranging from −0.03 to 0.03), thus confirming the robustness and performance of POLAC/PARASOL data to investigate the spatio-temporal variability of the aerosols over the study area. Regarding fine mode aerosol, POLAC/PARASOL data present a lower performance with correlation coefficient ranging from 0.37 to 0.73. Second, the analysis of POLAC/PARASOL aerosol climatology reveals a high contribution of the coarse mode of aerosols (AODc between 0.1 and 0.4) at long distance from the African sources, confirming previous studies related to dust transport. The POLAC/PARASOL data were also compared with aerosol data obtained over the North Tropical Atlantic Ocean from MACC and MERRA-2 reanalyses. It is observed that the total AOD is underestimated in both reanalysis with a negative bias reaching −0.2. In summary, our results thus suggest that satellite POLAC/PARASOL observations of fine and coarse modes of aerosols could provide additional constraints useful to improve the quantification of the dust direct radiative forcing on a regional scale but also the biogeochemical processes such as nutrient supply to the surface waters

Comparative allozyme and microsatellite population structure in a narrow endemic plant species, Centaurea corymbosa Pourret (Asteraceae)

International audienceCentaurea corymbosa Pourret (Asteraceae) is a narrow endemic species known only from six populations located in a 3-km2 area in the south of France. Earlier field experiments have suggested that pollen and seed dispersal were highly restricted within and among populations. Consistent with the field results, populations were highly differentiated for five allozyme loci and among-population variation fitted an isolation-by-distance model. In the present study, we investigated the genetic structure of C. corymbosa using six microsatellite loci. As with allozymes, microsatellites revealed no within-population structure and a large differentiation among populations. However, allozyme loci were less powerful than microsatellites in detecting the extent of gene flow assessed by assignment tests. The patterns of structuration greatly varied among loci for both types of marker; we suggest that differences in single-locus pattern could mainly be an effect of stochastic variation for allozymes and an effect of variation in mutation rate for microsatellites. In contrast to the multilocus results, the two most polymorphic microsatellite loci did not show any isolation-by-distance pattern. Our results suggest that highly variable loci might not always be the best suited markers to quantify levels of gene flow among populations

Repeated measures of traits, from C. diffusa common garden

Trait data for experimental populations of Centaurea diffusa, repeated measures. Trait values measured in common field experiment in Montpellier, France, 2011. File also include the first three principal components from the experimental PCA of the bioclimatic data for these populations

Data from: Adaptive plasticity and niche expansion in an invasive thistle

Phenotypic differentiation in size and fecundity between native and invasive populations of a species has been suggested as a causal driver of invasion in plants. Local adaptation to novel environmental conditions through a micro-evolutionary response to natural selection may lead to phenotypic differentiation and fitness advantages in the invaded range. Local adaptation may occur along a stress tolerance trade-off, favoring individuals that, in benign conditions, shift resource allocation from stress tolerance to increased vigor and fecundity and, therefore, invasiveness. Alternately, the typically disturbed invaded range may select for a plastic, generalist strategy, making phenotypic plasticity the main driver of invasion success. To distinguish between these hypotheses, we performed a field common garden and tested for genetically based phenotypic differentiation, resource allocation shifts in response to water limitation, and local adaptation to the environmental gradient which describes the source locations for native and invasive populations of diffuse knapweed (Centaurea diffusa). Plants were grown in an experimental field in France (naturalized range) under water addition and limitation conditions. After accounting for phenotypic variation arising from environmental differences among collection locations, we found evidence of genetic variation between the invasive and native populations for most morphological and life-history traits under study. Invasive C. diffusa populations produced larger, later maturing, and therefore potentially fitter individuals than native populations. Evidence for local adaptation along a resource allocation trade-off for water limitation tolerance is equivocal. However, native populations do show evidence of local adaptation to an environmental gradient, a relationship which is typically not observed in the invaded range. Broader analysis of the climatic niche inhabited by the species in both ranges suggests that the physiological tolerances of C. diffusa may have expanded in the invaded range. This observation could be due to selection for plastic, “general-purpose” genotypes with broad environmental tolerances

Inferring Population Decline and Expansion From Microsatellite Data: A Simulation-Based Evaluation of the Msvar Method

Reconstructing the demographic history of populations is a central issue in evolutionary biology. Using likelihood-based methods coupled with Monte Carlo simulations, it is now possible to reconstruct past changes in population size from genetic data. Using simulated data sets under various demographic scenarios, we evaluate the statistical performance of Msvar, a full-likelihood Bayesian method that infers past demographic change from microsatellite data. Our simulation tests show that Msvar is very efficient at detecting population declines and expansions, provided the event is neither too weak nor too recent. We further show that Msvar outperforms two moment-based methods (the M-ratio test and Bottleneck) for detecting population size changes, whatever the time and the severity of the event. The same trend emerges from a compilation of empirical studies. The latest version of Msvar provides estimates of the current and the ancestral population size and the time since the population started changing in size. We show that, in the absence of prior knowledge, Msvar provides little information on the mutation rate, which results in biased estimates and/or wide credibility intervals for each of the demographic parameters. However, scaling the population size parameters with the mutation rate and scaling the time with current population size, as coalescent theory requires, significantly improves the quality of the estimates for contraction but not for expansion scenarios. Finally, our results suggest that Msvar is robust to moderate departures from a strict stepwise mutation model

Past demographic history of Astrocaryum sciophilum: chloroplast genetic structure and restricted seed dispersal

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FranceCG - code

Github repository storing R scripts used in this paper