Inbreeding affects gene expression differently in two self-incompatible Arabidopsis lyrata populations with similar levels of inbreeding depression.

Knowledge of which genes and pathways are affected by inbreeding may help understanding the genetic basis of inbreeding depression, the potential for purging (selection against deleterious recessive alleles) and the transition from outcrossing to selfing. Arabidopsis lyrata is a predominantly self-incompatible perennial plant, closely related to the selfing model species A. thaliana. To examine how inbreeding affects gene expression, we compared the transcriptome of experimentally selfed and outcrossed A. lyrata originating from two Scandinavian populations that express similar inbreeding depression for fitness (∂≈0.80). The number of genes significantly differentially expressed between selfed and outcrossed individuals were 2.5 times higher in the Norwegian population (≈500 genes) than in the Swedish population (≈200 genes). In both populations a majority of genes were up-regulated upon selfing (≈80%). Functional annotation analysis of the differentially expressed genes showed that selfed offspring were characterized by (i) up-regulation of stress-related genes in both populations, and (ii) up-regulation of photosynthesis-related genes in Sweden but down-regulation in Norway. Moreover, we found that reproduction- and pollination-related genes were affected by inbreeding only in Norway. We conclude that inbreeding causes both general and population-specific effects. The observed common effects suggest that inbreeding generally up-regulates rather than down-regulates gene expression and affects genes associated with stress response and general metabolic activity. Population differences in number of affected genes and in effects on the expression of photosynthesis-related genes show that the genetic basis of inbreeding depression can differ between populations with very similar levels of inbreeding depression

Measuring, comparing and interpreting phenotypic selection on floral scent

Natural selection on floral scent composition is a key element of the hypothesis that pollinators and other floral visitors drive scent evolution. The measure of such selection is complicated by the high-dimensional nature of floral scent data and uncertainty about the cognitive processes involved in scent-mediated communication. We use dimension reduction through reduced-rank regression to jointly estimate a scent composite trait under selection and the strength of selection acting on this trait. To assess and compare variation in selection on scent across species, time and space, we reanalyse 22 datasets on six species from four previous studies. The results agreed qualitatively with previous analyses in terms of identifying populations and scent compounds subject to stronger selection but also allowed us to evaluate and compare the strength of selection on scent across studies. Doing so revealed that selection on floral scent was highly variable, and overall about as common and as strong as selection on other phenotypic traits involved in pollinator attraction or pollen transfer. These results are consistent with an important role of floral scent in pollinator attraction. Our approach should be useful for further studies of plant-animal communication and for studies of selection on other high-dimensional phenotypes. In particular, our approach will be useful for studies of pollinator-mediated selection on complex scent blends comprising many volatiles, and when no prior information on the physiological responses of pollinators to scent compounds is available

Measuring, comparing and interpreting phenotypic selection on floral scent

Natural selection on floral scent composition is a key element of the hypothesis that pollinators and other floral visitors drive scent evolution. The measure of such selection is complicated by the high-dimensional nature of floral scent data and uncertainty about the cognitive processes involved in scent-mediated communication. We use dimension reduction through reduced-rank regression to jointly estimate a scent composite trait under selection and the strength of selection acting on this trait. To assess and compare variation in selection on scent across species, time and space, we reanalyse 22 datasets on six species from four previous studies. The results agreed qualitatively with previous analyses in terms of identifying populations and scent compounds subject to stronger selection but also allowed us to evaluate and compare the strength of selection on scent across studies. Doing so revealed that selection on floral scent was highly variable, and overall about as common and as strong as selection on other phenotypic traits involved in pollinator attraction or pollen transfer. These results are consistent with an important role of floral scent in pollinator attraction. Our approach should be useful for further studies of plant-animal communication and for studies of selection on other high-dimensional phenotypes. In particular, our approach will be useful for studies of pollinator-mediated selection on complex scent blends comprising many volatiles, and when no prior information on the physiological responses of pollinators to scent compounds is available.Peer reviewe

Data from: There is more to pollinator-mediated selection than pollen limitation

Spatial variation in pollinator-mediated selection (Δβpoll) is a major driver of floral diversification, but we lack a quantitative understanding of its link to pollen limitation and net selection on floral traits. For 2-5 years, we quantified Δβpoll on floral traits in two populations each of two orchid species differing in pollen limitation. In both species, spatio-temporal variation in Δβpoll explained much of the variation in net selection. Selection was consistently stronger and the proportion that was pollinator-mediated was higher in the severely pollen-limited deceptive species than in the rewarding species. Within species, variation in pollen limitation could not explain variation in Δβpoll for any trait, indicating that factors influencing the functional relationship between trait variation and pollination success govern a major part of the observed variation in Δβpoll. Separating the effects of variation in mean interaction intensity and in the functional significance of traits will be necessary to understand spatio-temporal variation in selection exerted by the biotic environment

Data from: Non-linear costs of reproduction in a long-lived plant

A trade-off between current reproduction and future performance is a key component of life-history theory, but the shape of this trade-off for any specific fitness component remains elusive. We induced 3-5 levels of reproductive effort (RE) by manipulating fruit set of a long-lived orchid in two populations that differed in the length of the growing season and local climate, and examined survival, size and fecundity the following year. Natural fruit set was 72% higher in the long-season population, but was not associated with a significant survival cost in any population. Survival decreased linearly with experimentally increased RE in the short-season population. In both populations, natural RE incurred growth and fecundity costs, and growth costs increased non-linearly with diminishing costs at high RE. Fecundity costs increased linearly with RE in the long-season population, but non-linearly with diminishing costs at high RE in the other. The results demonstrate that the shape of the cost function may be non-linear with context-dependent intercept, slope and curvature. They are consistent with the prediction that survival costs appear only when RE exceeds natural levels, while growth and fecundity costs are evident at natural RE. Synthesis. We suggest that studies inducing multiple levels of RE are required to understand life-history trade-offs and their context-dependence. This kind of information is fundamental for an understanding of the link between environmental heterogeneity, adaptive differentiation and life-history evolution

Data from: Fine-scale genetic structure in the orchid Gymnadenia conopsea is not associated with local density of flowering plants

<p><span><strong>Premise</strong>:</span><span> Density-dependent pollinator visitation can lead to density-dependent mating patterns and within-population genetic structure. In Gymnadenia conopsea, individuals in low-density patches receive more self-pollen than individuals in high-density patches, suggesting higher relatedness at low density. Ongoing fragmentation is also expected to cause more local matings, potentially leading to biparental inbreeding depression.</span></p> <p><span><strong>Methods</strong>: </span><span>To evaluate whether relatedness decreases with local density, we analysed 1315 SNP loci in 113 individuals within two large populations. We quantified within-population genetic structure in one of the populations, recorded potential habitat barriers, and visualized gene flow using estimated effective migration surfaces (EEMS). We further estimated the magnitude of biparental inbreeding depression that would result from matings restricted to within 5 m.</span></p> <p><span><strong>Results</strong>: </span><span>There was no significant relationship between local density and relatedness in any population. We detected significant fine-scale genetic structure consistent with isolation-by-distance, with positive kinship coefficients at distances below 10 m. Kinship coefficients were low, and predicted biparental inbreeding depression resulting from matings within the closest 5 m was a modest 1–3%.</span> <span>EEMS suggested that rocks and bushes may act as barriers to gene flow within a population.</span></p> <p><span><strong>Conclusions</strong>: </span><span>The results suggest that increased self-pollen deposition in sparse patches does not necessarily cause higher selfing rates, or that inbreeding depression results in low establishment success of inbred individuals. The modest relatedness suggests that biparental inbreeding depression is unlikely to be an immediate problem following fragmentation of large populations. The results further indicate that habitat structure may contribute to governing fine-scale genetic structure in <em>G. conopsea</em>.</span></p><p>Funding provided by: Swedish Research Council for Environment Agricultural Sciences and Spatial Planning<br>Crossref Funder Registry ID: https://ror.org/03pjs1y45<br>Award Number: 2018-01397</p&gt

Fine-scale genetic structure in the orchid Gymnadenia conopsea is not associated with density of flowering plants

Premise: Density-dependent pollinator visitation can lead to density-dependent mating patterns and within-population genetic structure. In Gymnadenia conopsea, individuals in low-density patches receive more self pollen than individuals in high-density patches, suggesting higher relatedness at low density. Ongoing fragmentation is also expected to cause more local matings, potentially leading to biparental inbreeding depression. Methods: To evaluate whether relatedness decreases with local density, we analyzed 1315 SNP loci in 113 individuals within two large populations. We quantified within-population genetic structure in one of the populations, recorded potential habitat barriers, and visualized gene flow using estimated effective migration surfaces (EEMS). We further estimated the magnitude of biparental inbreeding depression that would result from matings restricted to within 5 m. Results: There was no significant relationship between local density and relatedness in any population. We detected significant fine-scale genetic structure consistent with isolation by distance, with positive kinship coefficients at distances below 10 m. Kinship coefficients were low, and predicted biparental inbreeding depression resulting from matings within the closest 5 m was a modest 1–3%. The EEMS suggested that rocks and bushes may act as barriers to gene flow within a population. Conclusions: The results suggest that increased self-pollen deposition in sparse patches does not necessarily cause higher selfing rates or that inbreeding depression results in low establishment success of inbred individuals. The modest relatedness suggests that biparental inbreeding depression is unlikely to be an immediate problem following fragmentation of large populations. The results further indicate that habitat structure may contribute to governing fine-scale genetic structure in G. conopsea