Plant performance under thermal stress : strategies and trade-offs, and their potential role in determining species distribution

The distribution of species is often restricted to a particular climatic zone with distribution boundaries following thermal isoclines. What hinders species from expanding their geographic distribution? To answer this question it is important to consider the traits of climate adaptation and their genetic architecture. For this, we used an integrative approach, combining common garden experiments and the analysis of the transcriptome based on RNA-sequencing to explore both phenotypic and genetic aspects of the thermal stress response. Study organism was the plant species Arabidopsis lyrata ssp. lyrata (Brassicaceae). Chapter 1 addressed the question of whether populations differed in thermal stress resistance and tolerance along two latitudinal clines and tested for the existence of trade-offs. A main result was that frost tolerance traded off against plant size in the absence of thermal stress. This genetically-based trade-off could be involved in constraining the evolution at the northern species border if selection favors fast development to large size at the cost of less frost tolerance. Chapter 2 focused on the acclimation process, its impact on thermal stress resistance, the cost and the underlying changes in gene expression. Acclimation increased thermal stress resistance independent of acclimation temperature. Furthermore, the plastic acclimation response did not seem to be costly. But a negative correlation between basal and induced resistance was found, which may constrain the evolution of acclimation. Chapter 3 explored genetic divergence in thermal resistance and tolerance and fitness related traits in a single population of a heterogeneous sand dune landscape. Overall, the work indicates high lability in the evolution of thermal stress-resistance strategies. Few constraints seem to exist, with the most important probably being one between frost tolerance and fast reproductive development

The effect of temperature and invasive alien predator on genetic and phenotypic variation in the damselfly Ischnura elegans : cross-latitude comparison

Abstract Background Understanding and predicting how organisms respond to human-caused environmental changes has become a major concern in conservation biology. Here, we linked gene expression and phenotypic data to identify candidate genes underlying existing phenotypic trait differentiation under individual and combined environmental variables. For this purpose, we used the damselfly Ischnura elegans. Egg clutches from replicated high- (southern Sweden) and central-latitude (southern Poland) populations facing different degrees of seasonal time constraints were collected. Damselfly larvae were exposed to experimental treatments: current and mild warming temperatures crossed with the presence or absence of an invasive alien predator cue released by the spiny-cheek crayfish, Faxonius limosus, which is only present in Poland to date. We measured the following traits: larval development time, body size, mass and growth rate, and used the larvae for gene expression analysis by RNA-seq. Data were analysed using a multivariate approach. Results We showed latitudinal differences in coping with mild warming and predator cues. When exposed to an increased temperature and a predator cue, central-latitude individuals had the shortest development and the fastest growth compared to high-latitude individuals. There was a general effect of predator cues regarding mass and growth rate reduction independent of latitude. Transcriptome analysis revealed that metabolic pathways related to larval anatomy and development tended to be upregulated in response to mild warming but only in fast-growing central-latitude individuals. Metabolic pathways linked to oxidative stress tended to be downregulated in response to a predator cue, especially in central-latitude individuals. Conclusion Different phenotypic and transcriptomic responses to environmental factors might be attributed to the variability in I. elegans life history strategies between the two latitudes caused by seasonal time constraints and to its coexistence with the invasive alien predator in nature. By providing insights into how organisms may respond to future anthropogenic changes, our results may be of particular interest in conservation biology.The research leading to these results was funded by the Norwegian Financial Mechanism 2014–2021, project no. 2019/34/H/NZ8/00683 (ECOPOND). S.S. was further supported by the National Science Centre, Poland (grant 2019/33/B/NZ8/00521) and Institute of Nature Conservation Polish Academy of Sciences

Table S3. Evol. app. Supplementary information

Table S3. Dataset used in Analysis 1 and Analysis 2, and summary of the sample size</p

Table S3. Evolutionary application - supplementary information

     Table S3. Dataset  used in Experiment 1 and Experiment 2, and summary of the sample size    </p

Genetic differentiation in life history traits and thermal stress performance across a heterogeneous dune landscape in Arabidopsis lyrata

Over very short spatial scales, the habitat of a species can differ in multiple abiotic and biotic factors. These factors may impose natural selection on several traits and can cause genetic differentiation within a population. We studied multivariate genetic differentiation in a plant species of a sand dune landscape by linking environmental variation with differences in genotypic trait values and gene expression levels to find traits and candidate genes of microgeographical adaptation. Maternal seed families of Arabidopsis lyrata were collected in Saugatuck Dunes State Park, Michigan, USA, and environmental parameters were recorded at each collection site. Offspring plants were raised in climate chambers and exposed to one of three temperature treatments: regular occurrence of frost, heat, or constant control conditions. Several traits were assessed: plant growth, time to flowering, and frost and heat resistance. The strongest trait-environment association was between a fast switch to sexual reproduction and weaker growth under frost, and growing in the open, away from trees. The second strongest association was between the trait combination of small plant size and early flowering under control conditions combined with large size under frost, and the combination of environmental conditions of growing close to trees, at low vegetation cover, on dune bottoms. Gene expression analysis by RNA-seq revealed candidate genes involved in multivariate trait differentiation. The results support the hypothesis that in natural populations, many environmental factors impose selection, and that they affect multiple traits, with the relative direction of trait change being complex. The results highlight that heterogeneity in the selection environment over small spatial scales is a main driver of the maintenance of adaptive genetic variation within populations

Genetic differentiation in life history traits and thermal stress performance across a heterogeneous dune landscape in Arabidopsis lyrata

Abstract Background and Aims Over very short spatial scales, the habitat of a species can differ in multiple abiotic and biotic factors. These factors may impose natural selection on several traits and can cause genetic differentiation within a population. We studied multivariate genetic differentiation in a plant species of a sand dune landscape by linking environmental variation with differences in genotypic trait values and gene expression levels to find traits and candidate genes of microgeographical adaptation. Methods Maternal seed families of Arabidopsis lyrata were collected in Saugatuck Dunes State Park, Michigan, USA, and environmental parameters were recorded at each collection site. Offspring plants were raised in climate chambers and exposed to one of three temperature treatments: regular occurrence of frost, heat, or constant control conditions. Several traits were assessed: plant growth, time to flowering, and frost and heat resistance. Key Results The strongest trait-environment association was between a fast switch to sexual reproduction and weaker growth under frost, and growing in the open, away from trees. The second strongest association was between the trait combination of small plant size and early flowering under control conditions combined with large size under frost, and the combination of environmental conditions of growing close to trees, at low vegetation cover, on dune bottoms. Gene expression analysis by RNA-seq revealed candidate genes involved in multivariate trait differentiation. Conclusions The results support the hypothesis that in natural populations, many environmental factors impose selection, and that they affect multiple traits, with the relative direction of trait change being complex. The results highlight that heterogeneity in the selection environment over small spatial scales is a main driver of the maintenance of adaptive genetic variation within populations

Thermal acclimation in Arabidopsis lyrata: genotypic costs and transcriptional changes.

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 preexposure 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 preexposure 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

Transcriptional activity of transposable elements along an elevational gradient in Arabidopsis arenosa

Background Plant genomes can respond rapidly to environmental changes and transposable elements (TEs) arise as important drivers contributing to genome dynamics. Although some elements were reported to be induced by various abiotic or biotic factors, there is a lack of general understanding on how environment influences the activity and diversity of TEs. Here, we combined common garden experiment with short-read sequencing to investigate genomic abundance and expression of 2245 consensus TE sequences (containing retrotransposons and DNA transposons) in an alpine environment in Arabidopsis arenosa. To disentangle general trends from local differentiation, we leveraged four foothill-alpine population pairs from different mountain regions. Seeds of each of the eight populations were raised under four treatments that differed in temperature and irradiance, two factors varying with elevation. RNA-seq analysis was performed on leaves of young plants to test for the effect of elevation and subsequently of temperature and irradiance on expression of TE sequences. Results Genomic abundance of the 2245 consensus TE sequences varied greatly between the mountain regions in line with neutral divergence among the regions, representing distinct genetic lineages of A. arenosa. Accounting for intraspecific variation in abundance, we found consistent transcriptomic response for some TE sequences across the different pairs of foothill-alpine populations suggesting parallelism in TE expression. In particular expression of retrotransposon LTR Copia (e.g. Ivana and Ale clades) and LTR Gypsy (e.g. Athila and CRM clades) but also non-LTR LINE or DNA transposon TIR MuDR consistently varied with elevation of origin. TE sequences responding specifically to temperature and irradiance belonged to the same classes as well as additional TE clades containing potentially stress-responsive elements (e.g. LTR Copia Sire and Tar, LTR Gypsy Reina). Conclusions Our study demonstrated that the A. arenosa genome harbours a considerable diversity of TE sequences whose abundance and expression response varies across its native range. Some TE clades may contain transcriptionally active elements responding to a natural environmental gradient. This may further contribute to genetic variation between populations and may ultimately provide new regulatory mechanisms to face environmental challenges

Locations of the nine North American <i>Arabidopsis lyrata</i> populations included in this study.

<p>The grey shading indicates the approximate distribution of the species based on herbarium records, regional botanical lists, personal communication with local botanists, and our own field experience. The actual distribution is highly fragmented. The eastern and western regions represent distinct ancestral genetic clusters [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0131808#pone.0131808.ref023" target="_blank">23</a>].</p

Latitude of origin of <i>Arabidopsis lyrata</i> plants differing in electrolyte leakage (a), asymptotic size (b), resistance to frost and heat based on electrolyte leakage (c), and tolerance to frost and heat based on asymptotic size (d).

<p>Symbols depict population means based on family means and one-/two-sided bars indicate standard errors. Regression lines on panels a and b represent the significant or close to significant latitude-by-treatment interaction, regression lines on panels c and d represent significant latitude effect. For statistics see Tables <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0131808#pone.0131808.t001" target="_blank">1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0131808#pone.0131808.t002" target="_blank">2</a>. Data for heat tolerance and frost resistance had been corrected for ancestral cluster.</p