The Experts below are selected from a list of 2412 Experts worldwide ranked by ideXlab platform

Outi Savolainen - One of the best experts on this subject based on the ideXlab platform.

  • Genomic patterns of local adaptation under gene flow in Arabidopsis Lyrata.
    Molecular biology and evolution, 2019
    Co-Authors: Tuomas Hämälä, Outi Savolainen
    Abstract:

    Short-scale local adaptation is a complex process involving selection, migration and drift. The expected effects on the genome are well grounded in theory but examining these on an empirical level has proven difficult, as it requires information about local selection, demographic history and recombination rate variation. Here, we use locally adapted and phenotypically differentiated Arabidopsis Lyrata populations from two altitudinal gradients in Norway to test these expectations at the whole-genome level. Demography modelling indicates that populations within the gradients diverged less than 2 kya and that the sites are connected by gene flow. The gene flow estimates are, however, highly asymmetric with migration from high to low altitudes being several times more frequent than vice versa. To detect signatures of selection for local adaptation, we estimate patterns of lineage specific differentiation among these populations. Theory predicts that gene flow leads to concentration of adaptive loci in areas of low recombination; a pattern we observe in both lowland-alpine comparisons. Although most selected loci display patterns of conditional neutrality, we found indications of genetic trade-offs, with one locus particularly showing high differentiation and signs of selection in both populations. Our results further suggest that resistance to solar radiation is an important adaptation to alpine environments, while vegetative growth and bacterial defense are indicated as selected traits in the lowland habitats. These results provide insights into genetic architectures and evolutionary processes driving local adaptation under gene flow. We also contribute to understanding of traits and biological processes underlying alpine adaptation in northern latitudes.

  • Local adaptation and ecological differentiation under selection, migration, and drift in Arabidopsis Lyrata.
    Evolution; international journal of organic evolution, 2018
    Co-Authors: Tuomas Hämälä, Tiina M. Mattila, Outi Savolainen
    Abstract:

    How the balance between selection, migration, and drift influences the evolution of local adaptation has been under intense theoretical scrutiny. Yet, empirical studies that relate estimates of local adaptation to quantification of gene flow and effective population sizes have been rare. Here, we conducted a reciprocal transplant trial, a common garden trial, and a whole-genome-based demography analysis to examine these effects among Arabidopsis Lyrata populations from two altitudinal gradients in Norway. Demography simulations indicated that populations within the two gradients are connected by gene flow (0.1 < 4Ne m < 11) and have small effective population sizes (Ne < 6000), suggesting that both migration and drift can counteract local selection. However, the three-year field experiments showed evidence of local adaptation at the level of hierarchical multiyear fitness, attesting to the strength of differential selection. In the lowland habitat, local superiority was associated with greater fecundity, while viability accounted for fitness differences in the alpine habitat. We also demonstrate that flowering time differentiation has contributed to adaptive divergence between these locally adapted populations. Our results show that despite the estimated potential of gene flow and drift to hinder differentiation, selection among these A. Lyrata populations has resulted in local adaptation.

  • Genome-Wide Analysis of Colonization History and Concomitant Selection in Arabidopsis Lyrata.
    Molecular biology and evolution, 2017
    Co-Authors: Jaakko S Tyrmi, Tiina M. Mattila, Tanja Pyhäjärvi, Outi Savolainen
    Abstract:

    The high climatic variability in the past hundred thousand years has affected the demographic and adaptive processes in many species, especially in boreal and temperate regions undergoing glacial cycles. This has also influenced the patterns of genome-wide nucleotide variation, but the details of these effects are largely unknown. Here we study the patterns of genome-wide variation to infer colonization history and patterns of selection of the perennial herb species Arabidopsis Lyrata, in locally adapted populations from different parts of its distribution range (Germany, UK, Norway, Sweden, and USA) representing different environmental conditions. Using site frequency spectra based demographic modeling, we found strong reduction in the effective population size of the species in general within the past 100,000 years, with more pronounced effects in the colonizing populations. We further found that the northwestern European A. Lyrata populations (UK and Scandinavian) are more closely related to each other than with the Central European populations, and coalescent based population split modeling suggests that western European and Scandinavian populations became isolated relatively recently after the glacial retreat. We also highlighted loci showing evidence for local selection associated with the Scandinavian colonization. The results presented here give new insights into postglacial Scandinavian colonization history and its genome-wide effects.

  • Role of seed germination in adaptation and reproductive isolation in Arabidopsis Lyrata.
    Molecular ecology, 2017
    Co-Authors: Päivi H. Leinonen, Helmi Kuittinen, Tiina M. Mattila, Tuomas Hämälä, Outi Savolainen
    Abstract:

    Seed germination is an important developmental and life history stage. Yet, the evolutionary impact of germination has mainly been studied in the context of dormancy, or for its role in reproductive isolation between species. Here, we aim to examine multiple consequences of genetic divergence on germination traits between two Arabidopsis Lyrata subspecies: ssp. petraea (Eurasia) and ssp. Lyrata (North America). Postdormancy germination time, a potentially adaptive trait, showed differentiation between the populations, and quantitative trait loci (QTL) mapping revealed that the trait variation is mainly controlled by two antagonistic loci. These QTL areas contain several candidate genes with known function in postdormancy germination in A. thaliana. The sequence variation of three genes was consistent with differential selection, and they also included fixed nonsynonymous substitutions with potential to account for the phenotypic differentiation. We further show that the divergence between the subspecies has led to a slight but significant reduction in hybrid germination proportions, indicating incipient reproductive isolation. Comparison of reciprocal F1 and F2 progenies suggests that Bateson-Dobzhansky-Muller incompatibilities likely act through uniparentally inherited factors. Examination of genomewide transmission ratio distortion further revealed that cytonuclear interactions cause substantial pregermination inviability in the hybrids. These results confirm that seed germination has adaptive potential beyond the dormancy stage and that hybrid seed inviability can be one of the first reproductive barriers to arise during divergence.

  • Cytoplasmic Male Sterility Contributes to Hybrid Incompatibility Between Subspecies of Arabidopsis Lyrata
    G3 (Bethesda Md.), 2013
    Co-Authors: Hans-peter Koelewijn, Esa A. Aalto, Outi Savolainen
    Abstract:

    In crosses between evolutionarily diverged populations, genomic incompatibilities may result in sterile hybrids, indicating evolution of reproductive isolation. In several plant families, crosses within a population can also lead to male sterile progeny because of conflict between the maternally and biparentally inherited genomes. We examined hybrid fertility between subspecies of the perennial outcrossing self-incompatible Lyrate rockcress (Arabidopsis Lyrata) in large reciprocal F2 progenies and three generations of backcrosses. In one of the reciprocal F2 progenies, almost one-fourth of the plants were male-sterile. Correspondingly, almost one-half of the plants in one of the four reciprocal backcross progenies expressed male sterility. In an additional four independent F2 and backcross families, three segregated male sterility. The observed asymmetrical hybrid incompatibility is attributable to male sterility factors in one cytoplasm, for which the other population lacks effective fertility restorers. Genotyping of 96 molecular markers and quantitative trait locus mapping revealed that only 60% of the plants having the male sterile cytoplasm and lacking the corresponding restorers were phenotypically male-sterile. Genotyping data showed that there is only one restorer locus, which mapped to a 600-kb interval at the top of chromosome 2 in a region containing a cluster of pentatricopeptide repeat genes. Male fertility showed no trade-off with seed production. We discuss the role of cytoplasm and genomic conflict in incipient speciation and conclude that cytoplasmic male sterility–lowering hybrid fitness is a transient effect with limited potential to form permanent reproductive barriers between diverged populations of hermaphrodite self-incompatible species.

Barbara K Mable - One of the best experts on this subject based on the ideXlab platform.

  • what causes mating system shifts in plants Arabidopsis Lyrata as a case study
    Heredity, 2017
    Co-Authors: Barbara K Mable, Detlef Weigel, Elizabeth Kilbride, Aileen Adam, Joerg Hagmann, Marc Stift
    Abstract:

    : The genetic breakdown of self-incompatibility (SI) and subsequent mating system shifts to inbreeding has intrigued evolutionary geneticists for decades. Most of our knowledge is derived from interspecific comparisons between inbreeding species and their outcrossing relatives, where inferences may be confounded by secondary mutations that arose after the initial loss of SI. Here, we study an intraspecific breakdown of SI and its consequences in North American Arabidopsis Lyrata to test whether: (1) particular S-locus haplotypes are associated with the loss of SI and/or the shift to inbreeding; (2) a population bottleneck may have played a role in driving the transition to inbreeding; and (3) the mutation(s) underlying the loss of SI are likely to have occurred at the S-locus. Combining multiple approaches for genotyping, we found that outcrossing populations on average harbour 5 to 9 S-locus receptor kinase (SRK) alleles, but only two, S1 and S19, are shared by most inbreeding populations. Self-compatibility (SC) behaved genetically as a recessive trait, as expected from a loss-of-function mutation. Bulked segregant analysis in SC × SI F2 individuals using deep sequencing confirmed that all SC plants were S1 homozygotes but not all S1 homozygotes were SC. This was also revealed in population surveys, where only a few S1 homozygotes were SC. Together with crossing data, this suggests that there is a recessive factor that causes SC that is physically unlinked to the S-locus. Overall, our results emphasise the value of combining classical genetics with advanced sequencing approaches to resolve long outstanding questions in evolutionary biology.

  • R-gene variation across Arabidopsis Lyrata subspecies: effects of population structure, selection and mating system
    BMC evolutionary biology, 2016
    Co-Authors: Eric B. Holub, James Buckley, Elizabeth Kilbride, Volkan Cevik, Joana G. Vicente, Barbara K Mable
    Abstract:

    Examining allelic variation of R-genes in closely related perennial species of Arabidopsis thaliana is critical to understanding how population structure and ecology interact with selection to shape the evolution of innate immunity in plants. We finely sampled natural populations of Arabidopsis Lyrata from the Great Lakes region of North America (A. l. Lyrata) and broadly sampled six European countries (A. l. petraea) to investigate allelic variation of two R-genes (RPM1 and WRR4) and neutral genetic markers (Restriction Associated DNA sequences and microsatellites) in relation to mating system, phylogeographic structure and subspecies divergence. Fine-scale sampling of populations revealed strong effects of mating system and population structure on patterns of polymorphism for both neutral loci and R-genes, with no strong evidence for selection. Broad geographic sampling revealed evidence of balancing selection maintaining polymorphism in R-genes, with elevated heterozygosity and diversity compared to neutral expectations and sharing of alleles among diverged subspecies. Codon-based tests detected both positive and purifying selection for both R-genes, as commonly found for animal immune genes. Our results highlight that combining fine and broad-scale sampling strategies can reveal the multiple factors influencing polymorphism and divergence at potentially adaptive genes such as R-genes.

  • reconstructing origins of loss of self incompatibility and selfing in north american Arabidopsis Lyrata a population genetic context
    Evolution, 2010
    Co-Authors: John Paul Foxe, Marc Stift, Annabelle Haudry, Andrew Tedder, Stephen I. Wright, Barbara K Mable
    Abstract:

    Theoretical and empirical comparisons of molecular diversity in selfing and outcrossing plants have primarily focused on long-term consequences of differences in mating system (between species). However, improving our understanding of the causes of mating system evolution requires ecological and genetic studies of the early stages of mating system transition. Here, we examine nuclear and chloroplast DNA sequences and microsatellite variation in a large sample of populations of Arabidopsis Lyrata from the Great Lakes region of Eastern North American that show intra- and interpopulation variation in the degree of self-incompatibility and realized outcrossing rates. Populations show strong geographic clustering irrespective of mating system, suggesting that selfing either evolved multiple times or has spread to multiple genetic backgrounds. Diversity is reduced in selfing populations, but not to the extent of the severe loss of variation expected if selfing evolved due to selection for reproductive assurance in connection with strong founder events. The spread of self-compatibility in this region may have been favored as colonization bottlenecks following glaciation or migration from Europe reduced standing levels of inbreeding depression. However, our results do not suggest a single transition to selfing in this system, as has been suggested for some other species in the Brassicaceae.

  • The effect of mating system on growth of Arabidopsis Lyrata in response to inoculation with the biotrophic parasite Albugo candida.
    Journal of evolutionary biology, 2010
    Co-Authors: P. N. Hoebe, Marc Stift, Eric B. Holub, Barbara K Mable
    Abstract:

    The effects of variation in host reproductive systems on response to pathogens are not well understood. We inoculated individuals from outcrossing and inbreeding populations of North American Arabidopsis Lyrata with Albugo candida (white blister rust) to test the effect of mating system and heterozygosity on disease response. We observed three host infection phenotypes, classified as fully resistant, partially resistant and fully susceptible. Overall, inbreeding populations had more susceptible and fewer partially resistant individuals than outcrossing populations, but the highest proportion of resistant individuals was found in two of the inbreeding populations. Mating system did not affect relative growth rate of inoculated plants, but there were strong effects of population and infection phenotype. We conclude that mating system per se does not determine the resistance of natural A. Lyrata populations to infection by Albugo, but that the increased variability in responses among inbreeding populations may be due to reduced effective population size.

  • patterns of genetic diversity in outcrossing and selfing populations of Arabidopsis Lyrata
    Molecular Ecology, 2007
    Co-Authors: Barbara K Mable, Aileen Adam
    Abstract:

    Arabidopsis Lyrata is normally considered an obligately outcrossing species with a strong self-incompatibility system, but a shift in mating system towards inbreeding has been found in some North American populations (subspecies A. Lyrata ssp. Lyrata ). This study provides a survey of the Great Lakes region of Canada to determine the extent of this mating system variation and how outcrossing rates are related to current population density, geographical distribution, and genetic diversity. Based on variation at microsatellite markers (progeny arrays to estimate multilocus outcrossing rates and population samples to estimate diversity measures) and controlled greenhouse pollinations, populations can be divided into two groups: (i) group A, consisting of individuals capable of setting selfed seed (including autogamous fruit set in the absence of pollinators), showing depressed outcrossing rates ( T m = 0.2–0.6), heterozygosity ( H O = 0.02–0.06) and genetic diversity ( H E = 0.08–0.10); and (ii) group B, consisting of individuals that are predominantly selfincompatible ( T m > 0.8), require pollinators for seeds set, and showing higher levels of heterozygosity ( H O = 0.13–0.31) and diversity ( H E = 0.19–0.410). Current population density is not related to the shift in mating system but does vary with latitude. Restricted gene flow among populations was evident among all but two populations ( F ST = 0.11–0.8). Group A populations were more differentiated from one another ( F ST = 0.78) than they were from group B populations ( F ST = 0.59), with 41% of the variation partitioned within populations, 47% between populations, and 12% between groups. No significant relationship was found between genetic and geographical distance. Results are discussed in the context of possible postglacial expansion scenarios in relation to loss of self-incompatibility.

Jon Ågren - One of the best experts on this subject based on the ideXlab platform.

  • similarity in g matrix structure among natural populations of Arabidopsis Lyrata
    Evolution, 2016
    Co-Authors: Gustaf Granath, Adriana Puentes, Jon Ågren
    Abstract:

    Understanding the stability of the G matrix in natural populations is fundamental for predicting evolutionary trajectories; yet, the extent of its spatial variation and how this impacts responses to selection remain open questions. With a nested paternal half-sib crossing design and plants grown in a field experiment, we examined differences in the genetic architecture of flowering time, floral display, and plant size among four Scandinavian populations of Arabidopsis Lyrata. Using a multivariate Bayesian framework, we compared the size, shape, and orientation of G matrices and assessed their potential to facilitate or constrain trait evolution. Flowering time, floral display and rosette size varied among populations and significant additive genetic variation within populations indicated potential to evolve in response to selection. Yet, some characters, including flowering start and number of flowers, may not evolve independently because of genetic correlations. Using a multivariate framework, we found few differences in the genetic architecture of traits among populations. G matrices varied mostly in size rather than shape or orientation. Differences in multivariate responses to selection predicted from differences in G were small, suggesting overall matrix similarity and shared constraints to trait evolution among populations.

  • Strong maternal effects on gene expression in Arabidopsis Lyrata hybrids
    Molecular biology and evolution, 2015
    Co-Authors: Elin Videvall, Jon Ågren, Nina Sletvold, Jenny Hagenblad, Bengt Hansson
    Abstract:

    Hybridization between populations or species can have pronounced fitness consequences. Yet little is known about how hybridization affects gene regulation. Three main models have been put forward to explain gene expression patterns in hybrids: additive, dominance or parental effects. Here we use high throughput RNA-sequencing to examine the extent to which hybrid gene expression follows predictions by each of the three models. We performed a reciprocal crossing experiment between two differentiated populations of the perennial herb Arabidopsis Lyrata and sequenced RNA in rosette leaves of twelve-week-old plants grown in greenhouse conditions. The two parental populations had highly differentiated gene expression patterns. In hybrids, a majority of genes showed intermediate expression relative to that of their parental populations (i.e. additive effects), but expression was frequently more similar to the maternal than to their paternal population (i.e. maternal effects). Allele-specific expression analyses showed that in the vast majority of cases, genes with pronounced maternal effect expressed both the maternal and the paternal allele. Maternal effects on hybrid gene expression have rarely been documented previously and our study suggests it could be more common than previously assumed. Whether the maternal effect on gene expression persists to later life-stages, and whether the variation in gene expression is manifested in other aspects of the phenotype, remain to be elucidated. Our findings are relevant for understanding the consequences of outbreeding and hybridization and open up several questions for future studies. (Less)

  • STRONG INBREEDING DEPRESSION IN TWO SCANDINAVIAN POPULATIONS OF THE SELF-INCOMPATIBLE PERENNIAL HERB Arabidopsis Lyrata
    Evolution; international journal of organic evolution, 2013
    Co-Authors: Nina Sletvold, Jenny Hagenblad, Bengt Hansson, Mathilde Mousset, Jon Ågren
    Abstract:

    Inbreeding depression is a key factor influencing mating system evolution in plants, but current understanding of its relationship with selfing rate is limited by a sampling bias with few estimates for self-incompatible species. We quantified inbreeding depression (δ) over two growing seasons in two populations of the self-incompatible perennial herb Arabidopsis Lyrata ssp. petraea in Scandinavia. Inbreeding depression was strong and of similar magnitude in both populations. Inbreeding depression for overall fitness across two seasons (the product of number of seeds, offspring viability, and offspring biomass) was 81% and 78% in the two populations. Chlorophyll deficiency accounted for 81% of seedling mortality in the selfing treatment, and was not observed among offspring resulting from outcrossing. The strong reduction in both early viability and late quantitative traits suggests that inbreeding depression is due to deleterious alleles of both large and small effect, and that both populations experience strong selection against the loss of self-incompatibility. A review of available estimates suggested that inbreeding depression tends to be stronger in self-incompatible than in self-compatible highly outcrossing species, implying that undersampling of self-incompatible taxa may bias estimates of the relationship between mating system and inbreeding depression.

  • Genetic consequences of seed banks in the perennial herb Arabidopsis Lyrata subsp. petraea (Brassicaceae)
    American journal of botany, 2011
    Co-Authors: Mohsen Falahati-anbaran, Jon Ågren, Sverre Lundemo, Hans K. Stenøien
    Abstract:

    Genetic consequences of seed banks in the perennial plant Arabidopsis Lyrata ssp. petraea (Brassicaceae).

  • Variation in tolerance to drought among Scandinavian populations of Arabidopsis Lyrata
    Evolutionary Ecology, 2011
    Co-Authors: Nina Sletvold, Jon Ågren
    Abstract:

    The ability to cope with water limitation influences plant distributions, and several plant traits have been interpreted as adaptations to drought stress. In Scandinavia, the perennial herb Arabidopsis Lyrata occurs in open habitats that differ widely in climate and water availability in summer, suggesting differential selection on drought-related traits. We conducted two greenhouse experiments to examine differentiation in drought response traits among six Scandinavian populations, and to determine whether leaf trichomes confer protection against drought. We quantified tolerance to drought as fitness (survival and biomass of survivors) when exposed to drought relative to fitness under non-drought conditions. Two Swedish populations from shores along the Bothnian Bay had higher tolerance to drought than four riverbed populations from Norway. Under conditions of drought, the shore populations experienced less leaf damage compared to the riverbed populations, and their survival and biomass were less reduced relative to non-drought conditions. Across populations, tolerance to drought was positively related to leaf mass per area and negatively related to flowering propensity and proportion roots, but not related to plant size at the initiation of the drought treatment. In populations polymorphic for trichome production, trichome-producing plants were more tolerant to drought than glabrous plants. The results suggest that both leaf morphology and life-history traits contribute to differential drought response in natural populations of A. Lyrata, and that this system offers excellent opportunities for examining the adaptive value and genetic basis of drought-related traits.

Yvonne Willi - One of the best experts on this subject based on the ideXlab platform.

  • lineage specific adaptation to climate involves flowering time in north american Arabidopsis Lyrata
    Molecular Ecology, 2020
    Co-Authors: Nora Walden, Kay Lucek, Yvonne Willi
    Abstract:

    Adaptation to local climatic conditions is commonly found within species, but whether it involves the same intraspecific genomic variants is unknown. We studied this question in North American Arabidopsis Lyrata, whose current distribution is shaped by post-glacial range expansion from two refugia, resulting in two distinct genetic clusters covering comparable climatic gradients. Using pooled whole-genome sequence data of 41 outcrossing populations, we identified loci associated with three niche-determining climatic variables in the two clusters and compared these outliers. Little evidence was found for parallelism in climate adaptation for single nucleotide polymorphisms (SNPs) and for genes with an accumulation of outlier SNPs. Significantly increased selection coefficients supported them as candidates of climate adaptation. However, the fraction of gene ontology (GO) terms shared between clusters was higher compared to outlier SNPs and outlier genes, suggesting that selection acts on similar pathways but not necessarily the same genes. Enriched GO terms involved responses to abiotic and biotic stress, circadian rhythm and development, with flower development and reproduction being among the most frequently detected. In line with GO enrichment, regulators of flowering time were detected as outlier genes. Our results suggest that while adaptation to environmental gradients on the genomic level are lineage-specific in A. Lyrata, similar biological processes seem to be involved. Differential loss of standing genetic variation, probably driven by genetic drift, can in part account for the lack of parallel evolution on the genomic level.

  • Postglacial ecotype formation under outcrossing and self-fertilization in Arabidopsis Lyrata.
    Molecular ecology, 2019
    Co-Authors: Kay Lucek, Nora Hohmann, Yvonne Willi
    Abstract:

    The formation of ecotypes has been invoked as an important driver of postglacial biodiversity, because many species colonized heterogeneous habitats and experienced divergent selection. Ecotype formation has been predominantly studied in outcrossing taxa, while far less attention has been paid to the implications of mating system shifts. Here, we addressed whether substrate‐related ecotypes exist in selfing and outcrossing populations of Arabidopsis Lyrata subsp. Lyrata and whether the genomic footprint differs between mating systems. The North American subspecies colonized both rocky and sandy habitats during postglacial range expansion and shifted the mating system from predominantly outcrossing to predominantly selfing in a number of regions. We performed an association study on pooled whole‐genome sequence data of 20 selfing or outcrossing populations, which suggested genes involved in adaptation to substrate. Motivated by enriched gene ontology terms, we compared root growth between plants from the two substrates in a common environment and found that plants originating from sand grew roots faster and produced more side roots, independent of mating system. Furthermore, single nucleotide polymorphisms associated with substrate‐related ecotypes were more clustered among selfing populations. Our study provides evidence for substrate‐related ecotypes in A. Lyrata and divergence in the genomic footprint between mating systems. The latter is the likely result of selfing populations having experienced divergent selection on larger genomic regions due to higher genome‐wide linkage disequilibrium.

  • Accumulation of transposable elements in selfing populations of Arabidopsis Lyrata supports the ectopic recombination model of transposon evolution
    New Phytologist, 2018
    Co-Authors: Georgi Bonchev, Yvonne Willi
    Abstract:

    Transposable elements (TE) can constitute a large fraction of plant genomes, yet our understanding of their evolution and fitness effect is still limited. Here we tested several models of evolution that make specific predictions about differences in TE abundance between selfing and outcrossing taxa, and between small and large populations. We estimated TE abundance in multiple populations of North American Arabidopsis Lyrata differing in mating system and long-term size, using transposon insertion display on several TE families. Selfing populations had higher TE copy numbers per individual and higher TE allele frequencies, supporting models which assume that selection against TEs acts predominantly against heterozygotes via the process of ectopic recombination. In outcrossing populations differing in long-term size, the data supported neither a model of density-regulated transposition nor a model of direct deleterious effect. Instead, the population structure of TEs revealed that outcrossing populations tended to split into western and eastern groups - as previously detected using microsatellite markers - whereas selfing populations from west and east were less differentiated. This, too, agrees with the model of ectopic recombination. Overall, our results suggest that TE elements are nearly neutral except for their deleterious potential to disturb meiosis in the heterozygous state.

  • Thermal acclimation in Arabidopsis Lyrata: genotypic costs and transcriptional changes.
    Journal of evolutionary biology, 2017
    Co-Authors: Guillaume Wos, Yvonne Willi
    Abstract:

    Frost and heat events can be challenging for sessile organisms that cannot escape thermal extremes. However, adverse effects of thermal stress on fitness may be reduced by pre-exposure to cold or heat, a process known as acclimation. To understand the ecological and evolutionary implications of acclimation, we investigated (1) the reduction in performance due to stress pre-exposure, (2) the magnitude of increased leaf resistance to subsequent stress, (3) the costs of acclimation and (4) the genes differing in expression due to stress pre-exposure. Plants of Arabidopsis Lyrata were raised under three treatments of pre-exposure: bouts of frost, bouts of heat or constant temperature. Resistance of leaves to subsequent frost and heat stress was then measured by electrolyte leakage. RNA-seq analysis was performed to examine the genes differentially expressed between stress-pre-exposed and control plants. Pre-exposure to stress during growth decreased plant size and increased leaf resistance to subsequent stress independent of whether pre-exposure was to frost or heat. But the highest increase in leaf resistance to frost was found after pre-exposure to frost (as a trend) and in leaf resistance to heat after pre-exposure to heat. No evidence for costs of acclimation was detected. RNA-sequencing suggested that acclimation by frost and heat pre-exposure was caused by distinct mechanisms: modification of the chloroplast membrane and modification of the cell wall and membrane, respectively. Our results suggest that thermal resistance is a labile complex of traits, strongly affected by the previously experienced stress environment, with undetermined costs.

  • Environmental marginality and geographic range limits: a case study with Arabidopsis Lyrata ssp. Lyrata
    Ecography, 2017
    Co-Authors: Julie A. Lee-yaw, Marco Fracassetti, Yvonne Willi
    Abstract:

    Understanding the factors that govern the distribution of species is a central goal of evolutionary ecology. It is commonly assumed that geographic range limits reflect ecological niche limits and that species experience increasingly marginal conditions towards the edge of their ranges. Using spatial data and ecological niche models we tested these hypotheses in Arabidopsis Lyrata. Specifically, we asked whether range limits coincide with predicted niche limits in this system and whether the suitability of sites declines towards the edge of the species’ range in North America. We further explored patterns of environmental change towards the edge of the range and asked whether genome-wide patterns of genetic diversity decline with increasing peripherality and environmental marginality. Our results suggest that latitudinal range limits coincide with niche limits. Populations experienced increasingly marginal environments towards these limits – though patterns of environmental change were more complex than most theoretical models for range limits assume. Genomic diversity declined towards the edge of the species’ range and with increasing distance from the estimated centre of the species’ niche in environmental space, but not with the suitability of sites based on niche model predictions. Thus while latitudinal range limits in this system are broadly associated with niche limits, the link between environmental conditions and genetic diversity (and thus the adaptive potential of populations) is less clear.

Marc Stift - One of the best experts on this subject based on the ideXlab platform.

  • no evidence for incipient speciation by selfing in north american Arabidopsis Lyrata
    Journal of Evolutionary Biology, 2021
    Co-Authors: Courtney E. Gorman, Marcel E. Dorken, Marc Stift
    Abstract:

    Self-fertilization inherently restricts gene flow by reducing the fraction of offspring that can be produced by inter-population matings. Therefore, mating system transitions from outcrossing to selfing could result in reproductive isolation between selfing and outcrossing lineages and provide a starting point for speciation. In newly diverged lineages, for example after a transition to selfing, further reproductive isolation can be caused by a variety of prezygotic and post-zygotic mechanisms that operate before, during and after pollination. In animals, prezygotic barriers tend to evolve faster than post-zygotic ones. This is not necessarily the case for plants, for which the relative importance of post-mating, post-fertilization and early-acting post-zygotic barriers has been investigated far less. To test whether post-pollination isolation exists between populations of North American Arabidopsis Lyrata that differ in breeding (self-incompatible versus self-compatible) and mating system (outcrossing versus selfing), we compared patterns of seed set after crosses made within populations, between populations of the same mating system and between populations with different mating systems. We found no evidence for post-pollination isolation between plants from selfing populations (self-compatible, low outcrossing rates) and outcrossing populations (self-incompatible, high outcrossing rates) via either prezygotic or early-acting post-zygotic mechanisms. Together with the results of other studies indicating the absence of reproductive barriers acting before and during pollination, we conclude that the transition to selfing in this study system has not led to the formation of reproductive barriers between selfing and outcrossing populations of North American A. Lyrata.

  • Limited phenological and pollinator-mediated isolation among selfing and outcrossing Arabidopsis Lyrata populations
    Proceedings. Biological sciences, 2020
    Co-Authors: Courtney E. Gorman, Lindsay Bond, Mark Van Kleunen, Marcel E. Dorken, Marc Stift
    Abstract:

    Transitions from outcrossing to selfing have been a frequent evolutionary shift in plants and clearly play a role in species divergence. However, many questions remain about the initial mechanistic basis of reproductive isolation during the evolution of selfing. For instance, how important are pre-zygotic pre-pollination mechanisms (e.g. changes in phenology and pollinator visitation) in maintaining reproductive isolation between newly arisen selfing populations and their outcrossing ancestors? To test whether changes in phenology and pollinator visitation isolate selfing populations of Arabidopsis Lyrata from outcrossing populations, we conducted a common garden experiment with plants from selfing and outcrossing populations as well as their between-population hybrids. Specifically, we asked whether there was isolation between outcrossing and selfing plants and their between-population hybrids through differences in (1) the timing or intensity of flowering; and/or (2) pollinator visitation. We found that phenology largely overlapped between plants from outcrossing and selfing populations. There were also no differences in pollinator preference related to mating system. Additionally, pollinators preferred to visit flowers on the same plant rather than exploring nearby plants, creating a large opportunity for self-fertilization. Overall, this suggests that pre-zygotic pre-pollination mechanisms do not strongly reproductively isolate plants from selfing and outcrossing populations of Arabidopsis Lyrata.

  • A shift towards the annual habit in selfing Arabidopsis Lyrata.
    Biology letters, 2020
    Co-Authors: Courtney E. Gorman, Mark Van Kleunen, Marcel E. Dorken, Christina Steinecke, Marc Stift
    Abstract:

    An annual life history is often associated with the ability to self-fertilize. However, it is unknown whether the evolution of selfing commonly precedes the evolution of annuality, or vice versa. Using a 2-year common garden experiment, we asked if the evolution of selfing in the normally perennial Arabidopsis Lyrata was accompanied by a shift towards the annual habit. Despite their very recent divergence from obligately outcrossing populations, selfing plants exhibited a 39% decrease in over-winter survival after the first year compared with outcrossing plants. Our data ruled out the most obvious underlying mechanism: differences in reproductive investment in the first year did not explain differences in survival. We conclude that transitions to selfing in perennial A. Lyrata may be accompanied by a shift towards annuality, but drivers of the process require further investigation.

  • limited phenological and pollinator mediated isolation among selfing and outcrossing Arabidopsis Lyrata populations
    bioRxiv, 2019
    Co-Authors: Courtney E. Gorman, Lindsay Bond, Mark Van Kleunen, Marcel E. Dorken, Marc Stift
    Abstract:

    Mating system transitions from outcrossing to selfing have been a frequent evolutionary shift in angiosperms and clearly play a role in species divergence. However, many questions remain about the initial mechanistic basis of reproductive isolation during the evolution of selfing. For instance, how important are prezygotic pre-pollination mechanisms (e.g., changes in phenology and pollinator visitation) in maintaining reproductive isolation between newly arisen selfing populations and their outcrossing ancestors? To test whether changes in phenology and pollinator visitation reproductively isolate selfing populations of Arabidopsis Lyrata from conspecific outcrossing populations, we conducted a common garden experiment in the native range with plants from selfing and outcrossing populations as well as their F1 hybrids. Hybrid plants resulting from crosses between self-incompatible populations had the highest probability of flowering. Time of peak flowering differed among mating systems although the magnitude of the difference was small. Flowering duration and maximum flower number did not strongly differ between mating systems and hybrids, and these phenological traits had little influence on the frequency of pollinator visits of either solitary bees or hoverflies. Additionally, pollinators preferred to visit flowers on the same plant (~50% of the time) rather than exploring nearby plants, regardless of whether they were of an alternative mating system type or F1 hybrids, creating a large opportunity for geitonogamy. Finally, by modelling pollen-transfer probabilities, we found no significant differences in the opportunity for pollinations between selfing and outcrossing plants. Overall, we found that selfing and outcrossing A. Lyrata populations show some phenological divergence but are likely only weakly prezygotically isolated via pre-pollination mechanisms.

  • Genetic interaction between two unlinked loci underlies the loss of self-incompatibility in Arabidopsis Lyrata
    2019
    Co-Authors: Mark Van Kleunen, Marc Stift
    Abstract:

    As the first step towards the evolution of selfing from obligate outcrossing, identifying the key mutations underlying the loss of self-incompatibility is of particular interest. However, our current knowledge is primarily based on sequence-based comparisons between selfing species and their self-incompatible relatives, which makes it hard to distinguish causal from secondary mutations. To by-pass this problem, we inferred the genetic basis of the loss of self-incompatibility by intercrossing plants from twelve geographically interspersed outcrossing and selfing populations of North-American Arabidopsis Lyrata and determining the breeding system of 1,607 progeny. Self-incompatibility was not restored after crosses between different self-compatible populations. Equal frequencies of self-compatible and self-incompatible progeny emerged from crosses between parents with different breeding systems. We propose a two-locus genetic model for the loss of self-incompatibility in which specific S-locus haplotypes (S1 and S19) are associated with loss of self-incompatibility through their interaction with an unlinked modifier.