Investigation of the geographical scale of adaptive phenological variation and its underlying genetics in Arabidopsis thaliana

International audienceDespite the increasing number of genomic tools, identifying the genetics underlying adaptive complex traits remains challenging in the model species Arabidopsis thaliana. This is due, at least in part, to the lack of data on the geographical scale of adaptive phenotypic variation. The aims of this study were (i) to tease apart the historical roles of adaptive and nonselective processes in shaping phenological variation in A. thaliana in France and (ii) to gain insights into the spatial scale of adaptive variation by identifying the putative selective agents responsible for this selection. Forty-nine natu- ral stands from four climatically contrasted French regions were characterized (i) phe- nologically for six traits, (ii) genetically using 135 SNP markers and (iii) ecologically for 42 variables. Up to 63% of phenological variation could be explained by neutral genetic diversity. The remaining phenological variation displayed stronger associations with ecological variation within regions than among regions, suggesting the impor- tance of local selective agents in shaping adaptive phenological variation. Although climatic conditions have often been suggested as the main selective agents acting on phenology in A. thaliana, both edaphic conditions and interspecific competition appear to be strong selective agents in some regions. In a first attempt to identify the genetics of phenological variation at different geographical scales, we phenotyped worldwide accessions and local polymorphic populations from the French RegMap in a genome- wide association (GWA) mapping study. The genomic regions associated with pheno- logical variation depended upon the geographical scale considered, stressing the need to account for the scale of adaptive phenotypic variation when choosing accession pan- els for GWAS

Does pre-dispersal seed predation limit reproduction and population growth in the alpine clonal plant Geum reptans?

We studied the impact of the seed damaging gall midge larva Geomyia alpina on its perennial alpine host plant Geum reptans. We analysed the effect of seed predation on reproduction by seeds, i.e. seed number, seed mass, and seed viability and on growth and clonal propagation of non-protected plants in comparison to plants protected from predation by an insecticide. Additionally, we assessed the consequences of seed predation for population growth using matrix projection modelling. Seed predation resulted in a decrease in total seed mass per flower head by 23.8% in non-protected plants (P > 0.05). Individual seed mass decreased with increasing infestation intensity (P > 0.05). Seed number remained unaffected because the sucking feeding behaviour by gall midge larvae does not evoke seed abortion. Percent germination of seeds from non-protected plants was reduced by 97.9% compared to seeds from protected plants. According to reduced seed viability, modelling revealed a decrease in population growth rate from lambda= 1.055 to lambda= 1.041. Predation did neither influence total plant biomass nor biomass fractions. But stolon dry-weight of non-protected plants increased by 24.1% (P > 0.05), which may indicate a trade-off between sexual reproduction and clonal propagation. Our results demonstrate that despite substantial reduction of viable seeds, predation by gall midge larvae only slightly affected population growth of G. reptans suggesting that in this alpine species, persistence by longevity and clonal propagation can balance potential seed losses by predation, at least for local population growth

Effects of habitat differences on the genetic diversity of Persicaria thunbergii

s This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.Abstract To understand the effects of habitat characteristics on the genetic diversity of Persicaria thunbergii, three sites of different environmental conditions in a water system were surveyed. Site A was the closest to the source of the water system, and there was a dam between sites A and B. Site C is located on the lowest downstream in the water system. Vegetation survey of four quadrats at each site was performed, and soil samples were collected for physicochemical analysis. Random amplification of polymorphic DNA (RAPD) analysis of ten P. thunbergii individuals at each site was conducted to calculate population genetic diversity and genetic distance among populations. Soil was sterile sand at site A, whereas loamy soil at sites B and C. A pure stand of P. thunbergii appeared at site A, while other species occurred together (such as Humulus japonicus and Phragmites australis) at sites B (Shannon-Wiener index; H B = 0.309) and C (H C = 0.299). Similar to the species diversity, genetic diversity (Neis gene diversity; h) within population of site A (h A = 0.2381) was relatively lower than sites B (h B = 0.2761) and C (h C = 0.2618). However, site C was separated from sites A and B in genetic distance rather than the geographical distance (Neis genetic distance; A~B, 0.0338; B~C, 0.0685; A~C, 0.0833)

Optimum reproduction and dispersal strategies of a clonal plant in a metapopulation : a simulation study with Hieracium pilosella

Clonal spread is favoured in many plants at the expense of seed production in order to expand rapidly into open habitats or to occupy space by forming dense patches. However, for the dynamics of a population in a patchy landscape seed dispersal remains important even for clonal plants. We used a spatially explicit individual-based metapopulation model to examine the consequences of two trade-offs in Hieracium pilosella L: first, between vegetative and sexual reproduction, and second, between short and far-distance dispersal of seeds. Our main question was, what are the environmental conditions that cause a mixed strategy of vegetative and sexual reproduction to be optimal. The model was parameterised with field data on local population dynamics of H. pilosella. Patch dynamics were given firstly by disturbance events that opened patches in a matrix of a clonal grass that were colonisable for H. pilosella, and secondly by the gradual disappearance of H. pilosella patches due to the expanding grass. Simulations revealed opposing selection pressures on traits determined by the two trade-offs. Vegetative reproduction is favoured by local dynamics, i.e. the need for maintenance and expansion of established populations, whereas seed production is favoured by the necessity to colonise empty habitats. Similar pressures act on the proportion of seeds dispersed over short and far distances. Optimum reproductive and dispersal strategies depended on habitat quality (determined by seedling establishment probability), the fraction of dispersed seeds, and the fraction of seeds lost on unsuitable ground. Under habitat conditions supporting moderate to low seedling establishment, between 20 to sexual reproduction with at least 10 distances suitable to attain empty patches. We conclude that in a spatially heterogeneous landscape sexual seed production in a clonal plant is advantageous even at the expense of local vegetative growth