Biology subjects

Ehlers, B. K.

Publications and source records attributed to Ehlers, B. K..

7 recordsLinked to original sources

bioRxiv2025

Ecological and Genetic Determinants of Essential Oil Diversity in Mediterranean Thymus

The Mediterranean Basin is a hotspot of plant diversity, with many species producing aromatic essential oils (EOs) that mediate ecological interactions and stress responses. Within Lamiaceae, the genus Thymus shows remarkable chemical variability, yet high intraspecific EO variation often limits its taxonomic resolution. We investigated EO composition, genetic structure, and environmental influences across 39 populations of Thymus sect. Mastichina in the Iberian Peninsula, using GC-MS alongside soil and climatic data to assess drivers of chemical variation and refine taxonomic characterization. We identified 14 major EO compounds, dominated by oxygenated monoterpenes. Most populations exhibited 1,8-cineole-rich chemotypes, yet seven populations showed linalool dominance, and multiple chemotypes often co-occurred within the same populations, revealing high intrapopulation chemical diversity. Minor compounds, including camphor, borneol, and camphene, varied among genetic clusters and were significantly correlated with temperature and precipitation gradients. Differences in EO composition were also detected between ploidy levels and genetic groups, although the major compounds (1,8-cineole and linalool) remained relatively consistent, indicating both conserved and locally adaptive chemical traits. These findings suggest that EO diversity in Thymus sect. Mastichina arises from a complex interplay of environmental conditions, genetic background, and ploidy. Integrating chemical, genetic, and ecological data provides a robust framework for understanding the evolutionary and ecological drivers of EO variation in Mediterranean aromatic plants, with implications for taxonomy, conservation, and the study of adaptive chemical traits.

evolutionary biology↗

bioRxiv2024

Natural variation in root exudate composition in the genetically structured Arabidopsis thaliana in the Iberian Peninsula

O_LIPlant root exudates are involved in nutrient acquisition, microbial partnerships, and inter- organism signaling. Yet, little is known about the genetic and environmental drivers of root exudate variation at large geographical scales, which may help understand evolutionary trajectories of plants in heterogeneous environments. C_LIO_LIWe quantified natural variation in chemical composition of Arabidopsis thaliana root exudates in 105 Iberian accessions. We identified up to 373 putative compounds using ultra-high performance liquid chromatography coupled with mass spectrometry. We estimated broad-sense heritability of compounds and conducted a genome-wide association (GWA) study. We associated variation in root exudates to variation in geographic, environmental, life history, and genetic attributes of Iberian accessions. C_LIO_LIOnly 25 of 373 compounds exhibited broad-sense heritability values significantly different from zero. GWA analysis identified polymorphisms associated to 12 root exudate compounds and 26 known genes involved in metabolism, defense, signaling, and nutrient transport. The genetic structure influenced root exudate composition involving terpenoids. We detected five terpenoids related to plant defense significantly varying in mean abundances in two genetic clusters. C_LIO_LIOur study provides first insights into the extent of root exudate natural variation at a regional scale depicting a diversified evolutionary trajectory among A. thaliana genetic clusters chiefly mediated by terpenoid composition. C_LI

plant biology↗

bioRxiv2024

Application of the thermal death time model in predicting thermal damage accumulation in plants

O_LIThe thermal death time (TDT) model suggests that the duration an organism can tolerate thermal stress decreases exponentially as the intensity of the temperature becomes more extreme. This model has been used to predict damage accumulation in ectotherm animals and plants under fluctuating thermal conditions. However, the critical assumption of the TDT model, which is additive damage accumulation, remains unverified for plants. C_LIO_LIWe assessed thermal damage in Thymus vulgaris under different heat and cold treatments and used TDT models to predict time to thermal failure of PSII. Additionally, thermal tolerance estimates from previous studies were used to create TDT models to assess the applicability of this framework in plants. C_LIO_LIWe show that thermal damage obtained at different stress intensities and durations is additive for both heat and cold stress, and that the TDT model can predict damage accumulation at both temperature extremes. Data from previous studies indicate a broad applicability of this approach across species, traits, and environments. C_LIO_LIThe TDT framework reveals a thermal tolerance landscape describing the exponential relationship between exposure duration, stress intensity and damage accumulation in plants. This thermal sensitivity emphasizes the potential impact of future thermal extremes on the mortality and distribution of plant species. C_LI HighlightThis study highlights the applicability of the thermal death time model to plants, unveiling a distinct thermal tolerance landscape, extending across species and traits for assessing thermal stress impacts.

plant biology↗

bioRxiv2022

Measuring plant diversity in a two-stage sampling design by Bayesian updated relative abundances

The two-stage sampling design provides good local estimates of both the number of plant species and the relative abundances. However, it is a problem to calculate Hill diversity indices at the local scale, because some of the species found in the large plot are not present in the small plot and such species should then incorrectly be weighted with zero relative abundance. A new method for calculating local Hill diversity indices from species richness and relative abundances data is therefore needed. We suggest to replace the local relative abundances with Bayesian updated relative abundance estimates, where the prior probability distribution of the relative abundances are empirically estimated from all plots of the same habitat types. The method is applied on Danish Nardus grasslands.

ecology↗

bioRxiv2020

Identity and provenance of neighbors, genotype-specific traits and abiotic stress affect intraspecific interactions in the annual legume Medicago truncatula

O_LIAccounting for intraspecific variation may improve our understanding of species coexistence. However, our knowledge of what factors maintain intraspecific variation is limited. We predicted that 1) a plant grows larger when with non-kin (i.e. different genotypes) than kin (i.e. same genotype) neighbors, 2) abiotic stress alters the outcome of kin vs. non-kin interactions, 3) genetic identity of plants affects composition of soil microbiome. C_LIO_LIWe set up mini-communities of Medicago truncatula, where focal genotypes were grown together with two kin or two non-kin neighbors from different origins. We analyzed how origin, identity of interacting genotypes and abiotic stress affected growth and fruit production. We also analyzed the composition of soil microbial communities. C_LIO_LIFocal plants grew larger in non-kin than in kin mini-communities. This pattern was stronger in low level of abiotic stress and when interacting genotypes were from similar origins. However, genotypic variation in growth and response to competition had a stronger effect on growth than mini-community type. Plant genotype identity did not affect soil microbiome. C_LIO_LIWe find that intraspecific variation is affected by genotype-specific traits and abiotic stress. Geographic, rather than genetic, distance among interacting genotypes affects the outcome of intraspecific interactions. C_LI

plant biology↗

bioRxiv2020

From genotype to phenotype: maintenance of a chemical polymorphism in the context of high geneflow.

A major question in evolution is how to maintain many adaptive phenotypes within a species. In Mediterranean wild thyme, a staggering number of discrete chemical phenotypes (chemotypes) coexist in close geographic proximity. Plant chemotypes are defined by the dominant monoterpene produced in their essential oil. We study the genetics of six distinct chemotypes nested within two well established ecotypes. Ecotypes, and chemotypes within ecotypes, are spatially segregated, and their distribution tracks local differences in the abiotic environment. The ecotypes have undergone a rapid shift in distribution associated with current climate change. Here, combining genomic, phenotypic, and environmental data, we show how the genetics of ecotype determination can allow for such rapid evolutionary response despite high gene flow among ecotypes. Variation in three terpene-synthase loci explains almost all variation in ecotype identity, with one single locus accounting for as much as 78% of it. Phenotypic selection on ecotypes combined with low segregating genotypic redundancy and tight genetic determination leaves a clear footprint at the genomic level: alleles associated with ecotype identity track environmental variation despite extensive gene flow. Different chemotypes, nested within each ecotype, also track environmental variation. However, in contrast to ecotypes, chemotype identity is determined by more loci and show a wider range of genotypic redundancy, which dilutes the impact of phenotypic selection on alleles associated with different chemotypes. Identifying the genetics behind this polymorphism in thyme is a crucial step towards understanding the maintenance of this widespread chemical polymorphism found in many aromatic Lamiaceae.

evolutionary biology↗

bioRxiv2019

Kin recognition and genetic variation for competitive ability in the annual legume Medicago minima

Knowing which mechanisms drive the outcome of intraspecific interactions is highly relevant for understanding diversity maintenance. Plant species that exhibit strong genetic substructure over small spatial scales may be exposed to frequent interactions with closely related individuals. Predictions of how genetic similarity may drive the outcome of intraspecific interactions are based on two contrasting theories: the resource partitioning hypothesis and kin selection theory. The first predicts that competition will be stronger among closely related conspecific (i.e. kin) because similar genotypes have similar resource requirements. The second predicts instead that competition will be reduced among kin, in order to maximize the inclusive fitness. Although efforts have been made to reconcile these two theories as non-mutually exclusive, the outcomes of intraspecific interaction studies are frequently interpreted as the results of either one or the other. We experimentally tested the hypothesis that intraspecific interactions may be driven by both genetic variation for competitive ability and reduced competition among kin. We used an annual legume, Medicago minima, to conduct two greenhouse experiments testing changes in root behaviour, above-ground growth and biomass in response to neighbour identity. We found evidence of both genetic variation for competitive ability and reduced competition among kin in some genotypes. Reduced competitive growth towards kin was found in the most competitive genotypes, suggesting that kin avoidance and competitive ability were simultaneously affecting plant behaviour and growth. With presence of both kin competition avoidance and variation for competitive ability, the outcome of intraspecific interactions will strongly depend on the local spatial genetic substructure. This is highly relevant to predict how intraspecific competition affect diversity maintenance.

ecology↗