Adaptive transgenerational plasticity in an annual plant: grandparental and parental drought stress enhance performance of seedlings in dry soil

Transgenerational plasticity to drought: contrasting patterns of non-genetic inheritance in two semi-arid Mediterranean shrubs

BACKGROUND AND AIMS

Intra- and transgenerational plasticity may provide substantial phenotypic variation to cope with environmental change. Since assessing the unique contribution of the maternal environment to the offspring phenotype is challenging in perennial, outcrossing plants, little is known about the evolutionary and ecological implications of transgenerational plasticity and its persistence over the life cycle in these species. We evaluated how intra- and transgenerational plasticity interplay to shape the adaptive responses to drought in two perennial Mediterranean shrubs.

METHODS

We used a novel common garden approach that reduced within-family genetic variation in both the maternal and offspring generations by growing the same maternal individual in two contrasting watering environments, well-watered and drought, in consecutive years. We then assessed phenotypic differences at the reproductive stage between offspring reciprocally grown in the same environments.

KEY RESULTS

Maternal drought had an effect on offspring performance only in Helianthemum squamatum. Offspring of drought-stressed plants showed more inflorescences, less sclerophyllous leaves and higher growth rates in both watering conditions, and heavier seeds under drought, than offspring of well-watered maternal plants. Maternal drought also induced similar plasticity patterns across maternal families, showing a general increase in seed mass in response to offspring drought, a pattern not observed in the offspring of well-watered plants. In contrast, both species expressed immediate adaptive plasticity, and the magnitude of intragenerational plasticity was larger than the transgenerational plastic responses.

CONCLUSIONS

Our results highlight that adaptive effects associated with maternal drought can persist beyond the seedling stage and provide evidence of species-level variation in the expression of transgenerational plasticity. Such differences between co-occurring Mediterranean species in the prevalence of this form of non-genetic inheritance may result in differential vulnerability to climate change.

Heritable responses to stress in plants

Most plants are adapted to their environments through generations of exposure to all elements. The adaptation process involves the best possible response to fluctuations in the environment based on the genetic and epigenetic make-up of the organism. Many plant species have the capacity to acclimate or adapt to certain stresses, allowing them to respond more efficiently, with fewer resources diverted from growth and development. However, plants can also acquire protection against stress across generations. Such a response is known as an intergenerational response to stress; typically, plants lose most of the tolerance in the subsequent generation when propagated without stress. Occasionally, the protection lasts for more than one generation after stress exposure and such a response is called transgenerational. In this review, we will summarize what is known about inter- and transgenerational responses to stress, focus on phenotypic and epigenetic events, their mechanisms and ecological and evolutionary meaning.

The agential perspective: Countermapping the modern synthesis

We compare and contrast two theoretical perspectives on adaptive evolution-the orthodox Modern Synthesis perspective, and the nascent Agential Perspective. To do so, we develop the idea from Rasmus Grønfeldt Winther of a 'countermap', as a means for comparing the respective ontologies of different scientific perspectives. We conclude that the modern Synthesis perspective achieves an impressively comprehensive view of a universal set of dynamical properties of populations, but at the considerable cost of radically distorting the nature of the biological processes that contribute to evolution. For its part, the Agential Perspective offers the prospect of representing the biological processes of evolution with much greater fidelity, but at the expense of generality. Trade-offs of this sort are endemic to science, and inevitable. Recognizing them helps us to avoid the pitfalls of 'illicit reification', i.e. the mistake of interpreting a feature of a scientific perspective as a feature of the non-perspectival world. We argue that much of the traditional Modern Synthesis representation of the biology of evolution commits this illicit reification.

San Diego Thornmint (Acanthomintha ilicifolia) Populations Differ in Growth and Reproductive Responses to Differential Water Availability: Evidence from a Common Garden Experiment

The responses of rare plants to environmental stressors will determine their potential to adapt to a rapidly changing climate. We used a common garden approach to evaluate how six populations of the annual San Diego thornmint (Acanthomintha ilicifolia Lamiaceae; listed as endangered in the state of California and as threatened by the US Fish and Wildlife Service) from across the species range respond in terms of growth (biomass, height, and width) and reproduction (seed production, floral production, and next generation seed viability) to experimental differences in water availability. We found a significant irrigation-by-population interaction on the aboveground growth, wherein the differences in the magnitude and direction of treatment did not correlate directly with climate variables in natural populations. With respect to reproduction, the low-irrigation treatment produced more seeds per plant, more reproductive individuals, and a larger proportion of viable seed in most, but not all, populations. The seed production and the effect of irrigation on seed production correlated positively with rainfall at wild source populations. These results suggest that Acanthomintha ilicifolia responds to water limitation by creating more and higher-quality seed, and that plants locally adapted to a higher annual rainfall show a greater plasticity to differences in water availability than plants adapted to a lower annual rainfall, a finding that can inform the in situ demographic management and ex situ collection strategy for Acanthomintha ilicifolia and other rare California annuals.

The relative impact of parental and current environment on plant transcriptomes depends on type of stress and genotype

Through developmental plasticity, an individual organism integrates influences from its immediate environment with those due to the environment of its parents. While both effects on phenotypes are well documented, their relative impact has been little studied in natural systems, especially at the level of gene expression. We examined this issue in four genotypes of the annual plant Persicaria maculosa by varying two key resources-light and soil moisture-in both generations. Transcriptomic analyses showed that the relative effects of parent and offspring environment on gene expression (i.e. the number of differentially expressed transcripts, DETs) varied both for the two types of resource stress and among genotypes. For light, immediate environment induced more DETs than parental environment for all genotypes, although the precise proportion of parental versus immediate DETs varied among genotypes. By contrast, the relative effect of soil moisture varied dramatically among genotypes, from 8-fold more DETs due to parental than immediate conditions to 10-fold fewer. These findings provide evidence at the transcriptomic level that the relative impacts of parental and immediate environment on the developing organism may depend on the environmental factor and vary strongly among genotypes, providing potential for the interplay of these developmental influences to evolve.

Intergenerational and transgenerational effects of drought stress on winter wheat (Triticum aestivum L.)

The environments where the progenitors are grown have the potential to affect the expression of traits in their offspring. Currently, there are various hypotheses regarding the evolutionary and ecological importance of stress memory effects. There is uncertainty regarding its occurrence, persistence, predictability, and adaptive value. In this study, 15 winter wheat cultivars were grown under drought and well-watered (control) treatments for two seasons to produce seeds with all possible combinations of drought exposure histories. A comprehensive analysis to estimate transgenerational (grandparental effects), intergenerational (parental effects), and their combined memory effects on offspring traits under both control and drought moisture treatments, was performed. There were significant memory effects in most of the evaluated traits ranging from +787% to -39.0% changes in both seed quality and plant traits. The expression of stress memory was highly dependent on the generation and number of exposures, traits, and seasons. Under drought treatment, the combination of grandparental and parental stress memories was additive in all traits, but their strengths were variable when considered separately. Stress memory enhanced the performance of offspring under similar stressful conditions: increased plant height, above-ground biomass, number of grains per plant, grain weight per plant and water potential. This study offers valuable new insights into the occurrence of drought stress memory, the complexities of the effects, possible physiological and metabolic alterations explaining the detected differences, and impacts toward a clearer understanding of their generation and context-dependency.

Weak transgenerational effects of ancestral nitrogen and phosphorus availabilities on offspring phenotypes in Arabidopsis thaliana

Nutrient availability significantly regulates plant growth and metabolic functions, but whether and how the long-term exposure of ancestral plants to contrasting nutrient environments influences offspring phenotypic performance (i.e., transgenerational plasticity) remain poorly addressed. Here we conducted experimental manipulations using Arabidopsis thaliana with the ancestral plants grown in different nitrogen (N) and phosphorus (P) availabilities over eleven consecutive generations, and then examined the offspring phenotypic performance under the interactive effects of current and ancestral nutrient environments. We found that current rather than ancestral nutrient environments dominantly explained the variations in offspring plant traits (i.e., flowering time, aboveground biomass and biomass allocation fractions), suggesting the relatively weak transgenerational effects of ancestral N and P availabilities on offspring phenotypes. In contrast, increasing N and P availabilities in the offspring generation remarkably shortened the flowering time, increased the aboveground biomass, and altered biomass allocation fractions differentially among organs. Despite the overall weak transgenerational phenotypic plasticity, under the low nutrient environment, the offspring of ancestral plants from the low nutrient environment had a significantly higher fruit mass fraction than those from the suitable nutrient environment. Taken together, our findings suggest that A. thaliana exhibits a much stronger within- than trans-generational trait plasticity under contrasting nutrient availabilities, and may provide important insights into the understanding of plant adaptation and evolutionary processes under changing nutrient environments.

Stress memory and its regulation in plants experiencing recurrent drought conditions

Developing stress-tolerant plants continues to be the goal of breeders due to their realized yields and stability. Plant responses to drought have been studied in many different plant species, but the occurrence of stress memory as well as the potential mechanisms for memory regulation is not yet well described. It has been observed that plants hold on to past events in a way that adjusts their response to new challenges without altering their genetic constitution. This ability could enable training of plants to face future challenges that increase in frequency and intensity. A better understanding of stress memory-associated mechanisms leading to alteration in gene expression and how they link to physiological, biochemical, metabolomic and morphological changes would initiate diverse opportunities to breed stress-tolerant genotypes through molecular breeding or biotechnological approaches. In this perspective, this review discusses different stress memory types and gives an overall view using general examples. Further, focusing on drought stress, we demonstrate coordinated changes in epigenetic and molecular gene expression control mechanisms, the associated transcription memory responses at the genome level and integrated biochemical and physiological responses at cellular level following recurrent drought stress exposures. Indeed, coordinated epigenetic and molecular alterations of expression of specific gene networks link to biochemical and physiological responses that facilitate acclimation and survival of an individual plant during repeated stress.

Maternal effects, paternal effects, and their interactions in the freshwater snail Physa acuta

Individuals exposed to predation risk can produce offspring with altered phenotypes. Most work on predation-induced parental effects has focused on maternal effects or on generalized parental effects where both parents are exposed to risk. We conducted an experiment to measure and compare maternal and paternal effects on offspring phenotypes and test for interactions in those effects. We exposed 82 snails from 22 lines to control or predator cues and created line dyads with the four possible mating pairings of control and predator cue exposed individuals. We measured the resulting body masses, shell masses, shell shapes, and anti-predator behaviors of the offspring. We found some evidence that offspring were larger and heavier when the mother was exposed to predation cues, but that this effect was negated when the father was also exposed. The mass of offspring shells relative to their total mass was unaffected by parental treatments. Shell shape was marginally affected by maternal treatment, but not paternal treatment. Behavioral responses to cues were not affected by maternal or paternal treatments. Our results suggest potential conflict between male and female parental effects and highlight the importance of examining the interactions of maternal and paternal effects.

Transcriptional memory of gene expression across generations participates in transgenerational plasticity of field pennycress in response to cadmium stress

Transgenerational plasticity (TGP) occurs when maternal environments influence the expression of traits in offspring, and in some cases may increase fitness of offspring and have evolutionary significance. However, little is known about the extent of maternal environment influence on gene expression of offspring, and its relationship with trait variations across generations. In this study, we examined TGP in the traits and gene expression of field pennycress (Thlaspi arvense) in response to cadmium (Cd) stress. In the first generation, along with the increase of soil Cd concentration, the total biomass, individual height, and number of seeds significantly decreased, whereas time to flowering, superoxide dismutase (SOD) activity, and content of reduced glutathione significantly increased. Among these traits, only SOD activity showed a significant effect of TGP; the offspring of Cd-treated individuals maintained high SOD activity in the absence of Cd stress. According to the results of RNA sequencing and bioinformatic analysis, 10,028 transcripts were identified as Cd-responsive genes. Among them, only 401 were identified as transcriptional memory genes (TMGs) that maintained the same expression pattern under normal conditions in the second generation as in Cd-treated parents in the first generation. These genes mainly participated in Cd tolerance-related processes such as response to oxidative stress, cell wall biogenesis, and the abscisic acid signaling pathways. The results of weighted correlation network analysis showed that modules correlated with SOD activity recruited more TMGs than modules correlated with other traits. The SOD-coding gene CSD2 was found in one of the modules correlated with SOD activity. Furthermore, several TMGs co-expressed with CSD2 were hub genes that were highly connected to other nodes and critical to the network's topology; therefore, recruitment of TMGs in offspring was potentially related to TGP. These findings indicated that, across generations, transcriptional memory of gene expression played an important role in TGP. Moreover, these results provided new insights into the trait evolution processes mediated by phenotypic plasticity.

Effects of parental drought on offspring fitness vary among populations of a crop wild relative

Transgenerational plasticity is a form of non-genetic inheritance that can reduce or enhance offspring fitness depending on parental stress. Yet, the adaptive value of such parental environmental effects and whether their expression varies among populations remain largely unknown. We used self-fertilized lines from climatically distinct populations of the crop wild relative Lupinus angustifolius. In the parental generation, full-siblings were grown in two contrasting watering environments. Then, to robustly separate the within-generation and transgenerational response to drought, we reciprocally assigned the offspring of parents to the same experimental treatments. We measured key functional traits and assessed lifetime reproductive fitness. Offspring of drought-stressed parents produced less reproductive biomass, but a similar number of lighter seeds, in dry soil compared to offspring of genetically identical, well-watered parents, an effect not mediated by differences in seed provisioning. Importantly, while the offspring of parents grown in the favourable environment responded to drought by slightly increasing individual seed mass, the pattern of plasticity of the offspring of drought-grown parents showed the opposite direction, and the negative effects of parental drought on seed mass were more pronounced in populations from cooler and moist habitats. Overall, our results show that parental effects may override immediate adaptive responses to drought and provide evidence of population-level variation in the expression of transgenerational plasticity.

Aphids and Mycorrhizal Fungi Shape Maternal Effects in Senecio vulgaris

Plant performance in any one generation is affected not only by the prevailing environmental conditions, but also by the conditions experienced by the parental generation of those plants. These maternal effects have been recorded in a many plant species, but the influence of external biotic (as opposed to abiotic) factors on shaping maternal effects have been rarely examined. Furthermore, almost all previous studies have taken place over one plant generation, rather than across multiple generations. Here, we studied the influence of insect herbivory and arbuscular mycorrhizal (AM) fungal colonisation on the shaping of maternal effects in the annual forb Senecio vulgaris. We grew plants with and without aphids (Myzus persicae) and AM fungi (hereafter termed ‘induction events’) over four successive generations, wherein seeds from plants in any one treatment were used to grow plants of the same treatment in the next generation, all in identical environmental conditions. We found strong evidence of maternal effects in the second plant generation, i.e., after one induction event. These plants took longer to germinate, flowered in a shorter time, produced lighter seeds and were shorter and of lower biomass than their parents. Aphid attack tended to enhance these effects, whereas AM fungi had little influence. However, thereafter there was a gradual recovery in these parameters, so that plants experiencing three inductions showed similar life history parameters to those in the original generation. We conclude that experiments investigating maternal effects need to be performed over multiple plant generations and that biotic factors such as insects and mycorrhizas must also be taken into account, along with abiotic factors, such as nutrient and water availability.

Nutrient Inputs Alleviate Negative Effects of Early and Subsequent Flooding on Growth of Polygonum hydropiper With the Aid of Adventitious Roots

Riparian plants are exposed to harmful stress induced by flooding, which is often accompanied by eutrophication in the Three Gorges Reservoir Region. The phenomenon is mainly caused by domestic sewage discharges, slow water flow, and agricultural fertilizer pollution. Simulating abiotic stress, such as flooding at the initial period, can act as a signal and induce positive responses of plants to subsequent severe stress. In addition, eutrophication supplies nutrients, provides a favorable environment in the early stages of plant, and facilitates good performance in later development. However, whether early flooding (with or without eutrophication) acts as positive cue or as stress on plants at different developmental stages remains unclear. To address this question, seeds of Polygonum hydropiper were collected from low and high elevations in the hydro-fluctuation belt of the Three Gorges Reservoir Region. Plants germinated from these seeds were subjected to shallower and shorter early flooding treatments with or without eutrophication. Subsequently, plants were subjected to deeper and longer flooding treatments with or without eutrophication. Early flooding and eutrophic flooding significantly induced generation of adventitious roots, suggesting morphological adaptation to flooding. Although early flooding and eutrophic flooding treatments did not increase plant biomass in subsequent treatments compared with control, stem length, length and width of the 1st fully expanded leaf, and biomass of plants in the early eutrophic treatment were higher than these of the early flooding treatment plants. These results suggest a negative lag-effect of early flooding, and also indicate that nutrient inputs can alleviate such effects. Similarly, subsequent eutrophic flooding also enhanced plant growth compared with subsequent flooding, showing significantly higher values of leaf traits and adventitious root number. Plants originated from low elevation had significantly higher functional leaf length and stem biomass compared with those from high elevation. These results suggest that nutrient inputs can alleviate negative effects of early and subsequent flooding on growth of P. hydropiper with the generation of adventitious roots.

Clonal Parental Effects on Offspring Growth of Different Vegetative Generations in the Aquatic Plant Pistia stratiotes

Parental (environmental) effects can modify the growth of offspring, which may play an essential role in their adaptation to environmental variation. While numerous studies have tested parental effects on offspring growth, most have considered offspring growth of only one generation and very few have considered offspring growth of different generations. We conducted a greenhouse experiment with an aquatic clonal plant Pistia stratiotes. We grew a single ramet of P. stratiotes under low or high nutrients, the initial (parent) ramets produced three different generations of offspring ramets, and these offspring ramets were also subjected to the same two nutrient levels. High nutrients currently experienced by the offspring increased biomass accumulation and ramet number of all three offspring generations of P. stratiotes. However, these positive effects on biomass were greater when the offspring ramets originated from the parent ramets grown under low nutrients than when they were produced by the parent ramets grown under high nutrients. These results suggest that parental effects can impact the performance of different offspring generations of clonal plants. However, heavier offspring ramets produced under high nutrients in parental conditions did not increase the subsequent growth of the offspring generations. This finding indicates that parental provisioning in favorable conditions may not always increase offspring growth, partly depending on root allocation but not ramet size such as ramet biomass.

Multivariate selection mediated by aridity predicts divergence of drought-resistant traits along natural aridity gradients of an invasive weed

Geographical variation in the environment underpins selection for local adaptation and evolutionary divergence among populations. Because many environmental conditions vary across species' ranges, identifying the specific environmental variables underlying local adaptation is profoundly challenging. We tested whether natural selection mediated by aridity predicts clinal divergence among invasive populations of capeweed (Arctotheca calendula) that established and spread across southern Australia during the last two centuries. Using common garden experiments with two environmental treatments (wet and dry) that mimic aridity conditions across capeweed's invasive range, we estimated clinal divergence and effects of aridity on fitness and multivariate phenotypic selection in populations sampled along aridity gradients in Australia. We show that: (1) capeweed populations have relatively high fitness in aridity environments similar to their sampling locations; (2) the magnitude and direction of selection strongly differs between wet and dry treatments, with drought stress increasing the strength of selection; and (3) differences in directional selection between wet and dry treatments predict patterns of clinal divergence across the aridity gradient, particularly for traits affecting biomass, flowering phenology and putative antioxidant expression. Our results suggest that aridity-mediated selection contributes to trait diversification among invasive capeweed populations, possibly facilitating the expansion of capeweed across southern Australia.

The Effect of Temperature and Water Stresses on Seed Germination and Seedling Growth of Wheat (Triticum aestivum L.)

Temperature and moisture are essential factors in germination and seedling growth. The purpose of this research was to assess the germination and growth of wheat (Triticum aestivum L.) seeds under various abiotic stressors. It was conducted in the Agronomy Institute of the Hungarian University of Agriculture and Life Sciences, Gödöllő, Hungary. Six distinct temperature levels were used: 5, 10, 15, 20, 25, and 30 °C. Stresses of drought and waterlogging were quantified using 25 water levels based on single-milliliter intervals and as a percentage based on thousand kernel weight (TKW). Seedling density was also tested. Temperature significantly influenced germination duration and seedling development. 20 °C was ideal with optimal range of 15 °C to less than 25 °C. Germination occurred at water amount of 75% of the TKW, and its ideal range was lower and narrower than the range for seedling development. Seed size provided an objective basis for defining germination water requirements. The current study established an optimal water supply range for wheat seedling growth of 525–825 percent of the TKW. Fifteen seeds within a 9 cm Petri dish may be preferred to denser populations.

Evolution of anticipatory effects mediated by epigenetic changes

Anticipatory effects mediated by epigenetic changes occur when parents modify the phenotype of their offspring by making epigenetic changes in their gametes, guided by information from an environmental cue. To investigate when do anticipatory effects mediated by epigenetic changes evolve in a fluctuating environment, I use an individual-based simulation model with explicit genetic architecture. The model allows for the population to respond to environmental changes by evolving plasticity, bet hedging, or by tracking the environment with genetic adaptation, in addition to the evolution of anticipatory effects. The results show that anticipatory effects evolve when the environmental cue provides reliable information about the environment and the environment changes at intermediate rates, provided that fitness costs of anticipatory effects are rather low. Moreover, evolution of anticipatory effects is quite robust to different genetic architectures when reliability of the environmental cue is high. Anticipatory effects always give smaller fitness benefits than within-generation plasticity, suggesting a possible reason for generally small observed anticipatory effects in empirical studies.

Transgenerational effects of temperature fluctuations in Arabidopsis thaliana

Plant stress responses can extend into the following generations, a phenomenon called transgenerational effects. Heat stress, in particular, is known to affect plant offspring, but we do not know to what extent these effects depend on the temporal patterns of the stress, and whether transgenerational responses are adaptive and genetically variable within species. To address these questions, we carried out a two-generation experiment with nine Arabidopsis thaliana genotypes. We subjected the plants to heat stress regimes that varied in timing and frequency, but not in mean temperature, and we then grew the offspring of these plants under controlled conditions as well as under renewed heat stress. The stress treatments significantly carried over to the offspring generation, with timing having stronger effects on plant phenotypes than stress frequency. However, there was no evidence that transgenerational effects were adaptive. The magnitudes of transgenerational effects differed substantially among genotypes, and for some traits the strength of plant responses was significantly associated with the climatic variability at the sites of origin. In summary, timing of heat stress not only directly affects plants, but it can also cause transgenerational effects on offspring phenotypes. Genetic variation in transgenerational effects, as well as correlations between transgenerational effects and climatic variability, indicates that transgenerational effects can evolve, and have probably already done so in the past.

Bridging the explanatory gaps: What can we learn from a biological agency perspective?

We begin this article by delineating the explanatory gaps left by prevailing gene-focused approaches in our understanding of phenotype determination, inheritance, and the origin of novel traits. We aim not to diminish the value of these approaches but to highlight where their implementation, despite best efforts, has encountered persistent limitations. We then discuss how each of these explanatory gaps can be addressed by expanding research foci to take into account biological agency-the capacity of living systems at various levels to participate in their own development, maintenance, and function by regulating their structures and activities in response to conditions they encounter. Here we aim to define formally what agency and agents are and-just as importantly-what they are not, emphasizing that agency is an empirical property connoting neither intention nor consciousness. Lastly, we discuss how incorporating agency helps to bridge explanatory gaps left by conventional approaches, highlight scientific fields in which implicit agency approaches are already proving valuable, and assess the opportunities and challenges of more systematically incorporating biological agency into research programs.

Genetic differences in the temporal and environmental stability of transgenerational environmental effects

Environments influence the expression of phenotypes of individuals, their progeny, and even their grandprogeny. The duration of environmental effects and how they are modified by subsequent environments are predicted to be targets of natural selection in variable environments. However, little is known about the genetic basis of the temporal persistence of environmental effects and their stability of expression across subsequent environments, or even the extent to which natural genotypes differ in these attributes of environmental effects. We factorially manipulated the thermal environment experienced in three successive generations, to quantify the temporal persistence and environmental stability of temperature effects in contrasting genotypes of Arabidopsis thaliana. We found that genotypes differed in the manner in which environmental effects dissipated across successive generations, the manner in which responses to ancestral environments were stably expressed in present environments, the manner in which ancestral environments altered responses to present environments, and in the manner in which ancestral environments altered fitness in present conditions. Genetic variation exists in nature for these trait-specific environmental responses, suggesting that the temporal persistence and stability of environmental effects in variable environments have the potential to evolve in response to natural selection imposed by different environments and sequences of environments.

Transgenerational effects of parent plant competition on offspring development in contrasting conditions

Conditions during a parent's lifetime can induce phenotypic changes in offspring, providing a potentially important source of variation in natural populations. Yet, to date, biotic factors have seldom been tested as sources of transgenerational effects in plants. In a greenhouse experiment with the generalist annual Polygonum persicaria, we tested for effects of parental competition on offspring by growing isogenic parent plants either individually or in competitive arrays and comparing their seedling progeny in contrasting growth environments. Offspring of competing vs. non-competing parents showed significantly altered development, resulting in greater biomass and total leaf area, but only when growing in neighbor or simulated canopy shade, rather than sunny dry conditions. A follow-up experiment in which parent plants instead competed in dry soil found that offspring in dry soil had slightly reduced growth, both with and without competitors. In neither experiment were effects of parental competition explained by changes in seed provisioning, suggesting a more complex mode of regulatory inheritance. We hypothesize that parental competition in moist soil (i.e., primarily for light) confers specific developmental effects that are beneficial for light-limited offspring, while parental competition in dry soil (i.e., primarily for belowground resources) produces offspring of slightly lower overall quality. Together, these results indicate that competitive conditions during the parental generation can contribute significantly to offspring variation, but these transgenerational effects will depend on the abiotic resources available to both parents and progeny.

The 'black box' of plant demography: how do seed type, climate and seed fungal communities affect grass seed germination?

Demographic studies measure drivers of plant fecundity including seed production and survival, but few address both abiotic and biotic drivers of germination such as variation in climate among sites, population density, maternal plants, seed type and fungal pathogen abundance. We examined germination and microbial communities of seeds of Danthonia californica, which are either chasmogamous (external, wind-pollinated) or cleistogamous (internal, self-fertilized) and Festuca roemeri, which are solely chasmogamous. Seed populations were sourced across environmental gradients. We tested germination and used high-throughput sequencing to characterize seed fungal community structure. For F. roemeri, maternal plants significantly influenced germination as did climate and pathogens; germination increased from wetter, cooler sites. For D. californica, the main drivers of germination were maternal plant, seed type and pathogens; on average, more chasmogamous seeds germinated. Fungal communities depended largely on seed type, with fewer fungi associated with cleistogamous seeds, but the communities also depended on site factors such as vapor pressure deficit, plant density and whether the seeds had germinated. Putative pathogens that were negatively correlated with germination were more abundant for both D. californica and F. roemeri chasmogamous seeds than D. californica cleistogamous seeds. In D. californica, cleistogamous and chasmogamous seeds contain vastly different fungal communities.

Maternal effects and the outcome of interspecific competition

Maternal environmental effects create lagged population responses to past environments. Although they are ubiquitous and vary in expression across taxa, it remains unclear if and how their presence alters competitive interactions in ecological communities.Here, we use a discrete-time competition model to simulate how maternal effects alter competitive dynamics in fluctuating and constant environments. Further, we explore how omitting maternal effects alter estimates of known model parameters from observational time series data.Our simulations demonstrate that (i) maternal effects change competitive outcomes, regardless of whether competitors otherwise interact neutrally or exhibit non-neutral competitive differences, (ii) the consequences of maternal effects for competitive outcomes are mediated by the temporal structure of environmental variation, (iii) even in constant conditions, competitive outcomes are influenced by species' maternal effects strategies, and (iv) in observational time series data, omitting maternal effects reduces variation explained by models and biases parameter estimates, including competition coefficients.Our findings demonstrate that the ecological consequences of maternal effects hinge on the competitive environment. Evolutionary biologists have long recognized that maternal effects can be an important but often overlooked strategy buffering populations from environmental change. We suggest that maternal effects are similarly critical to ecology and call for research into maternal effects as drivers of dynamics in populations and communities.

Maternal effects strengthen interactions of temperature and precipitation, determining seed germination of dominant alpine grass species

PREMISE

Despite the existence of many studies on the responses of plant species to climate change, there is a knowledge gap on how specific climatic factors and their interactions regulate seed germination in alpine species. This understanding is complicated by the interplay between responses of seeds to the environment experienced during germination, the environment experienced by the maternal plant during seed development and genetic adaptations of the maternal plant to its environment of origin.

METHODS

The study species (Anthoxanthum alpinum, A. odoratum) originated from localities with factorial combinations of temperature and precipitation. Seed germination was tested in conditions simulating the extreme ends of the current field conditions and a climate change scenario. We compared the performance of field-collected seeds with that of garden-collected seeds.

RESULTS

A change to warmer and wetter conditions resulted in the highest germination of A. alpinum, while A. odoratum germinated the most in colder temperature and with home moisture. The maternal environment did have an impact on plant performance of the study species. Field-collected seeds of A. alpinum tolerated warmer conditions better than those from the experimental garden.

CONCLUSIONS

The results demonstrate how knowledge of responses to climate change can increase our ability to understand and predict the fate of alpine species. Studies that aim to understand the germination requirements of seeds under future climates should use experimental designs allowing the separation of genetic differentiation, plasticity and maternal effects and their interactions, since all these mechanisms play an important role in driving species' germination patterns.

Small RNAs and their targets are associated with the transgenerational effects of water-deficit stress in durum wheat

Water-deficit stress negatively affects wheat yield and quality. Abiotic stress on parental plants during reproduction may have transgenerational effects on progeny. Here we investigated the transgenerational influence of pre-anthesis water-deficit stress by detailed analysis of the yield components, grain quality traits, and physiological traits in durum wheat. Next-generation sequencing analysis profiled the small RNA-omics, mRNA transcriptomics, and mRNA degradomics in first generation progeny. Parental water-deficit stress had positive impacts on the progeny for traits including harvest index and protein content in the less stress-tolerant variety. Small RNA-seq identified 1739 conserved and 774 novel microRNAs (miRNAs). Transcriptome-seq characterised the expression of 66,559 genes while degradome-seq profiled the miRNA-guided mRNA cleavage dynamics. Differentially expressed miRNAs and genes were identified, with significant regulatory patterns subject to trans- and inter-generational stress. Integrated analysis using three omics platforms revealed significant biological interactions between stress-responsive miRNA and targets, with transgenerational stress tolerance potentially contributed via pathways such as hormone signalling and nutrient metabolism. Our study provides the first confirmation of the transgenerational effects of water-deficit stress in durum wheat. New insights gained at the molecular level indicate that key miRNA-mRNA modules are candidates for transgenerational stress improvement.

Transgenerational Induction of Resistance to Phytophthora cinnamomi in Holm Oak

The maternal environment of a tree species can influence the development and resistance of its offspring. Transgenerational induction of resistance is well known in plants but its occurrence in forest tree species has been less reported. Quercus ilex L. (holm oak) is a widespread Mediterranean tree species threatened by the invasive Phytophthora cinnamomi Rands pathogen. The influence of P. cinnamomi on the offspring of infected Q. ilex mother trees has not been studied. This study compared the performance and tolerance to P. cinnamomi of seedlings from non-infected and P. cinnamomi-infected trees. Acorns from Q. ilex trees were collected from five forests. After isolations were conducted in the rhizosphere of several trees, in each forest, three trees were selected as non-infected and three were selected as P. cinnamomi-infected. Forty acorns per tree were weighed and sown under greenhouse conditions, and when plants were aged ~9 months they were challenged with P. cinnamomi. Plant mortality was higher in the offspring of non-infected trees than in the offspring of P. cinnamomi-infected trees (26.2% vs. 21.1%, respectively). Consistently, survival probabilities of seedlings from P. cinnamomi-infected trees were higher than those of seedlings from non-infected trees, particularly in seedlings with reduced growth. Although acorns from healthy Q. ilex trees were heavier than acorns from P. cinnamomi-infected trees, the time to death of inoculated seedlings was not influenced by seed weight. The time to death of seedlings was positively related to belowground mass, particularly to an increased proportion of fine secondary roots. We report transgenerational-induced resistance to P. cinnamomi in Q. ilex triggered by an unknown mechanism independent of acorn mass. Information about the persistence of transgenerational effects in Q. ilex offspring and the influence of these effects on plant fitness is crucial to improve the management and regeneration of this declining species.

Predictability of Biotic Stress Structures Plant Defence Evolution

To achieve ecological and reproductive success, plants need to mitigate a multitude of stressors. The stressors encountered by plants are highly dynamic but typically vary predictably due to seasonality or correlations among stressors. As plants face physiological and ecological constraints in responses to stress, it can be beneficial for plants to evolve the ability to incorporate predictable patterns of stress in their life histories. Here, we discuss how plants predict adverse conditions, which plant strategies integrate predictability of biotic stress, and how such strategies can evolve. We propose that plants commonly optimise responses to correlated sequences or combinations of herbivores and pathogens, and that the predictability of these patterns is a key factor governing plant strategies in dynamic environments.

Reproductive performance in successive generations of the brine shrimp Artemia salina (Crustacea: Anostraca) from the Sebkha of Sidi El Hani (Tunisia)

Artemia salina cysts collected from the Sebkha of Sidi El Hani hatched and cultivated in the laboratory were investigated. Nauplii were acclimated to laboratory conditions until reproductively mature (Generation 1; G1). Reproductive performance in terms of total cysts and nauplii offspring, days between brood production, and cyst and nauplii numbers was evaluated. Nauplii produced by specimens in the G1 were defined as those of G2 with there also being third (G3) and fourth (G4) generations. The aims were to evaluate Artemia salina in aquaculture conditions with the long-term aim of developing a system for "artemiculture". There was a larger number of cysts or nauplii per brood between G1 (60.7 ± 10.9 nauplii or cysts/female) and subsequent generations, notably G2 (122 nauplii or cysts/female, P <  0.05). The mean number of cysts and nauplii per female increased from the first and last brood. Number of cysts produced per female increased markedly (P <  0.05) from G1 (54.5 ± 14.2) to G3 (128.9 ± 39.2). Percentage of females producing nauplii increased from G1 (20 %) to G4 (100 %). There was, therefore, an increase in percentage of ovoviviparous offspring (nauplii) per female (P <  0.05) from G1 (7%) to G4 (71 %). There were no differences, however, between mean numbers of broods per female, and numbers of days between broods. The results indicate there are variations in reproduction from oviparity to ovoviviparity as consecutive generations of Artemia salina are cultivated. In summary, there was a rapid adaptation of Artemia salina of Sidi El Hani to laboratory conditions.

Costs and Benefits of Transgenerational Induced Resistance in Arabidopsis

Recent evidence suggests that stressed plants employ epigenetic mechanisms to transmit acquired resistance traits to their progeny. However, the evolutionary and ecological significance of transgenerational induced resistance (t-IR) is poorly understood because a clear understanding of how parents interpret environmental cues in relation to the effectiveness, stability, and anticipated ecological costs of t-IR is lacking. Here, we have used a full factorial design to study the specificity, costs, and transgenerational stability of t-IR following exposure of Arabidopsis thaliana to increasing stress intensities by a biotrophic pathogen, a necrotrophic pathogen, and salinity. We show that t-IR in response to infection by biotrophic or necrotrophic pathogens is effective against pathogens of the same lifestyle. This pathogen-mediated t-IR is associated with ecological costs, since progeny from biotroph-infected parents were more susceptible to both necrotrophic pathogens and salt stress, whereas progeny from necrotroph-infected parents were more susceptible to biotrophic pathogens. Hence, pathogen-mediated t-IR provides benefits when parents and progeny are in matched environments but is associated with costs that become apparent in mismatched environments. By contrast, soil salinity failed to mediate t-IR against salt stress in matched environments but caused non-specific t-IR against both biotrophic and necrotrophic pathogens in mismatched environments. However, the ecological relevance of this non-specific t-IR response remains questionable as its induction was offset by major reproductive costs arising from dramatically reduced seed production and viability. Finally, we show that the costs and transgenerational stability of pathogen-mediated t-IR are proportional to disease pressure experienced by the parents, suggesting that plants use disease severity as an environmental proxy to adjust investment in t-IR.

Effects of fragmentation of clones compound over vegetative generations in the floating plant Pistia stratiotes

BACKGROUND AND AIMS

Clonal plants dominate many plant communities, especially in aquatic systems, and clonality appears to promote invasiveness and to affect how diversity changes in response to disturbance and resource availability. Understanding how the special physiological and morphological properties of clonal growth lead to these ecological effects depends upon studying the long-term consequences of clonal growth properties across vegetative generations, but this has rarely been done. This study aimed to show how a key clonal property, physiological integration between connected ramets within clones, affects the response of clones to disturbance and resources in an aquatic, invasive, dominant species across multiple generations.

METHODS

Single, parental ramets of the floating stoloniferous plant Pistia stratiotes were grown for 3 weeks, during which they produced two or three generations of offspring; connections between new ramets were cut or left intact. Individual offspring were then used as parents in a second 3-week iteration that crossed fragmentation with previous fragmentation in the first iteration. A third iteration yielded eight treatment combinations, zero to three rounds of fragmentation at different times in the past. The experiment was run once at a high and once at a low level of nutrients.

RESULTS

In each iteration, fragmentation increased biomass of the parental ramet, decreased biomass of the offspring and increased number of offspring. These effects persisted and compounded from one iteration to another, though more recent fragmentation had stronger effects, and were stronger at the low than at the high nutrient level. Fragmentation did not affect net accumulation of mass by groups after one iteration but increased it after two iterations at low nutrients, and after three iterations at both nutrient levels.

CONCLUSIONS

Both the positive and negative effects of fragmentation on clonal performance can compound and persist over time and can be stronger when resource levels are lower. Even when fragmentation has no short-term net effect on clonal performance, it can have a longer-term effect. In some cases, fragmentation may increase total accumulation of mass by a clone. The results provide the first demonstration of how physiological integration in clonal plants can affect fitness across generations and suggest that increased disturbance may promote invasion of introduced clonal species via effects on integration, perhaps especially at lower nutrient levels.

Understanding 'Non-genetic' Inheritance: Insights from Molecular-Evolutionary Crosstalk

Understanding the evolutionary and ecological roles of 'non-genetic' inheritance (NGI) is daunting due to the complexity and diversity of epigenetic mechanisms. We draw on insights from molecular and evolutionary biology perspectives to identify three general features of 'non-genetic' inheritance systems: (i) they are functionally interdependent with, rather than separate from, DNA sequence; (ii) precise mechanisms vary phylogenetically and operationally; and (iii) epigenetic elements are probabilistic, interactive regulatory factors and not deterministic 'epialleles' with defined genomic locations and effects. We discuss each of these features and offer recommendations for future empirical and theoretical research that implements a unifying inherited gene regulation (IGR) approach to studies of 'non-genetic' inheritance.

Proteomic analysis of wheat seeds produced under different nitrogen levels before and after germination

The objective of this study was to investigate differentially abundant proteins (DAPs) of wheat seeds produced under two nitrogen levels (0 and 240 kg/ha) before and after germination. We selected samples at 8 and 72 h after imbibition (HAI) to identify DAPs by iTRAQ. The results showed 190 and 124 DAPs at 8 and 72 HAI, respectively. Alpha-gliadin and chlorophyll a-b binding protein showed the biggest difference in abundance before and after germination. In GO enrichment analysis, the most significantly enriched GO term was nutrient reservoir activity at 8 HAI and endopeptidase inhibitor activity at 72 HAI. Moreover, many DAPs involved in mobilization of stored nutrients and photosynthesis were mapped to KEGG pathways. Dough development time, dough stability time and seedling chlorophyll content under N240 were significantly higher than those under N0, which validated the results of proteomic analysis. These results are crucial for food nutrition and food processing.

Genotypic variation in the persistence of transgenerational responses to seasonal cues

Phenotypes respond to environments experienced directly by an individual, via phenotypic plasticity, or to the environment experienced by ancestors, via transgenerational environmental effects. The adaptive value of environmental effects depends not only on the strength and direction of the induced response but also on how long the response persists within and across generations, and how stably it is expressed across environments that are encountered subsequently. Little is known about the genetic basis of those distinct components, or even whether they exhibit genetic variation. We tested for genetic differences in the inducibility, temporal persistence, and environmental stability of transgenerational environmental effects in Arabidopsis thaliana. Genetic variation existed in the inducibility of transgenerational effects on traits expressed across the life cycle. Surprisingly, the persistence of transgenerational effects into the third generation was uncorrelated with their induction in the second generation. Although environmental effects for some traits in some genotypes weakened over successive generations, others were stronger or even in the opposite direction in more distant generations. Therefore, transgenerational effects in more distant generations are not merely caused by the retention or dissipation of those expressed in prior generations, but they may be genetically independent traits with the potential to evolve independently.

Remember where you came from: ABA insensitivity is epigenetically inherited in mesophyll, but not seeds

Plants transmit their experiences of environmental conditions to their progeny through epigenetic inheritance, improving their progeny's fitness under prevailing conditions. Though ABA is known to regulate epigenetic-modification genes, no strong phenotypic link between those genes and intergenerational "memory" has been shown. Previously, we demonstrated that mesophyll insensitivity to ABA (FBPase::abi1-1{fa} transgenic plants) results in a range of developmental phenotypes, including early growth vigor and early flowering (i.e., stress-escape behavior). Here, we show that null plants, used as controls (segregates of FBPase::abi1 that are homozygote descendants of a heterozygous transgenic plant, but do not contain the transformed abi1-1 gene) phenotypically resembled their FBPase::abi1-1 parents. However, in germination and early seedling development assays, null segregants resembled WT plants. These FBPase::abi1-1 null segregants mesophyll-related phenotypes were reproducible and stable for at least three generations. These results suggest that the heritability of stress response is linked to ABA's epigenetic regulatory effect through ABI1 and mesophyll-related traits. The discrepancy between the epigenetic heritability of seed and mesophyll-related traits is an example of the complexity of epigenetic regulation, which is both gene and process-specific, and may be attributed to the fine-tuning of tradeoffs between flowering time, growth rate and levels of risk that allow annual plants to optimize their fitness in uncertain environments.

Transgenerational effects of parental light environment on progeny competitive performance and lifetime fitness

Plant and animal parents may respond to environmental conditions such as resource stress by altering traits of their offspring via heritable non-genetic effects. While such transgenerational plasticity can result in progeny phenotypes that are functionally pre-adapted to the inducing environment, it is unclear whether such parental effects measurably enhance the adult competitive success and lifetime reproductive output of progeny, and whether they may also adversely affect fitness if offspring encounter contrasting conditions. In glasshouse experiments with inbred genotypes of the annual plant Polygonum persicaria, we tested the effects of parental shade versus sun on (a) competitive performance of progeny in shade, and (b) lifetime reproductive fitness of progeny in three contrasting treatments. Shaded parents produced offspring with increased fitness in shade despite competition, as well as greater competitive impact on plant neighbours. Inherited effects of parental light conditions also significantly altered lifetime fitness: parental shade increased reproductive output for progeny in neighbour and understorey shade, but decreased fitness for progeny in sunny, dry conditions. Along with these substantial adaptive and maladaptive transgenerational effects, results show complex interactions between genotypes, parent environment and progeny conditions that underscore the role of environmental variability and change in shaping future adaptive potential. This article is part of the theme issue 'The role of plasticity in phenotypic adaptation to rapid environmental change'.

Empirical patterns of environmental variation favor adaptive transgenerational plasticity

Effects of parental environment on offspring traits have been well known for decades. Interest in this transgenerational form of phenotypic plasticity has recently surged due to advances in our understanding of its mechanistic basis. Theoretical research has simultaneously advanced by predicting the environmental conditions that should favor the adaptive evolution of transgenerational plasticity. Yet whether such conditions actually exist in nature remains largely unexplored. Here, using long-term climate data, we modeled optimal levels of transgenerational plasticity for an organism with a one-year life cycle at a spatial resolution of 4 km2 across the continental United States. Both annual temperature and precipitation levels were often autocorrelated, but the strength and direction of these autocorrelations varied considerably even among nearby sites. When present, such environmental autocorrelations render offspring environments statistically predictable based on the parental environment, a key condition for the adaptive evolution of transgenerational plasticity. Results of our optimality models were consistent with this prediction: High levels of transgenerational plasticity were favored at sites with strong environmental autocorrelations, and little-to-no transgenerational plasticity was favored at sites with weak or nonexistent autocorrelations. These results are among the first to show that natural patterns of environmental variation favor the evolution of adaptive transgenerational plasticity. Furthermore, these findings suggest that transgenerational plasticity is likely variable in nature, depending on site-specific patterns of environmental variation.

No evidence for local adaptation and an epigenetic underpinning in native and non-native ruderal plant species in Germany

Many invasive species have rapidly adapted to different environments in their new ranges. This is surprising, as colonization is usually associated with reduced genetic variation. Heritable phenotypic variation with an epigenetic basis may explain this paradox.Here, we assessed the contribution of DNA methylation to local adaptation in native and naturalized non-native ruderal plant species in Germany. We reciprocally transplanted offspring from natural populations of seven native and five non-native plant species between the Konstanz region in the south and the Potsdam region in the north of Germany. Before the transplant, half of the seeds were treated with the demethylation agent zebularine. We recorded survival, flowering probability, and biomass production as fitness estimates.Contrary to our expectations, we found little evidence for local adaptation, both among the native and among the non-native plant species. Zebularine treatment had mostly negative effects on overall plant performance, regardless of whether plants were local or not, and regardless of whether they were native or non-native. Synthesis. We conclude that local adaptation, at least at the scale of our study, plays no major role in the success of non-native and native ruderal plants. Consequently, we found no evidence yet for an epigenetic basis of local adaptation.

Drought soil legacy overrides maternal effects on plant growth

Maternal effects (i.e. trans-generational plasticity) and soil legacies generated by drought and plant diversity can affect plant performance and alter nutrient cycling and plant community dynamics. However, the relative importance and combined effects of these factors on plant growth dynamics remain poorly understood.We used soil and seeds from an existing plant diversity and drought manipulation field experiment in temperate grassland to test maternal, soil drought and diversity legacy effects, and their interactions, on offspring plant performance of two grassland species (Alopecurus pratensis and Holcus lanatus) under contrasting glasshouse conditions.Our results showed that drought soil legacy effects eclipsed maternal effects on plant biomass. Drought soil legacy effects were attributed to changes in both abiotic (i.e. nutrient availability) and biotic soil properties (i.e. microbial carbon and enzyme activity), as well as plant root and shoot atom 15N excess. Further, plant tissue nutrient concentrations and soil microbial C:N responses to drought legacies varied between the two plant species and soils from high and low plant diversity treatments. However, these diversity effects did not affect plant root or shoot biomass.These findings demonstrate that while maternal effects resulting from drought occur in grasslands, their impacts on plant performance are likely minor relative to drought legacy effects on soil abiotic and biotic properties. This suggests that soil drought legacy effects could become increasingly important drivers of plant community dynamics and ecosystem functioning as extreme weather events become more frequent and intense with climate change. A plain language summary is available for this article.

An Integrative Framework for Understanding the Mechanisms and Multigenerational Consequences of Transgenerational Plasticity

Transgenerational plasticity (TGP) occurs when the environment experienced by a parent influences the development of their offspring. In this article, we develop a framework for understanding the mechanisms and multi-generational consequences of TGP. First, we conceptualize the mechanisms of TGP in the context of communication between parents (senders) and offspring (receivers) by dissecting the steps between an environmental cue received by a parent and its resulting effects on the phenotype of one or more future generations. Breaking down the problem in this way highlights the diversity of mechanisms likely to be involved in the process. Second, we review the literature on multigenerational effects and find that the documented patterns across generations are diverse. We categorize different multigenerational patterns and explore the proximate and ultimate mechanisms that can generate them. Throughout, we highlight opportunities for future work in this dynamic and integrative area of study.

Effects of maternal and grandmaternal flea infestation on offspring quality and quantity in a desert rodent: evidence for parasite-mediated transgenerational phenotypic plasticity

Parasites can cause a broad range of sublethal fitness effects across a wide variety of host taxa. However, a host's efforts to compensate for possible parasite-induced fitness effects are less well-known. Parental effects may beneficially alter the offspring phenotype if parental environments sufficiently predict the offspring environment. Parasitism is a common stressor across generations; therefore, parental infestation could reliably predict the likelihood of infestation for offspring. However, little is known about relationships between parasitism and transgenerational phenotypic plasticity. Thus, we investigated how maternal and grandmaternal infestation with fleas (Xenopsylla ramesis) affected offspring quality and quantity in a desert rodent (Meriones crassus). We used a fully-crossed design with control and infested treatments to examine litter size, pup body mass at birth, and pup mass gain before weaning for combinations of maternal and grandmaternal infestation status. No effect of treatment on litter size or pup body mass at birth was found. However, maternal and grandmaternal infestation status significantly affected pre-weaning body mass gain, a proxy for the rate of maturation, in male pups. Pups gained significantly more weight before weaning if maternal and grandmaternal infestation statuses matched, regardless of the treatment. Thus, pups whose mothers and grandmothers experienced similar risks of parasitism, either both non-parasitized or both infested, would reach sexual maturity more quickly than those pups whose mothers' infestation status did not match that of their grandmothers. These results support the contention that parents can receive external cues such as the risk of parasitism, that prompt them to alter offspring provisioning. Therefore, parasites could be a mediator of environmentally-induced maternal effects and could affect host reproductive fitness across multiple generations.

Parental experience modifies the Mimulus methylome

BACKGROUND

Transgenerational plasticity occurs when the environmental experience of an organism modifies the growth and development of its progeny. Leaf damage in Mimulus guttatus exhibits transgenerational plasticity mediated through differential expression of hundreds of genes. The epigenetic mechanisms that facilitate this response have yet to be described.

RESULTS

We performed whole genome bisulfite sequencing in the progeny of genetically identical damaged and control plants and developed a pipeline to compare differences in the mean and variance of methylation between treatment groups. We find that parental damage increases the variability of CG and CHG methylation among progeny, but does not alter the overall mean methylation. Instead it has positive effects in some regions and negative in others. We find 3,396 CHH, 203 CG, and 54 CHG Differentially Methylated Regions (DMRs) ranging from tens to thousands of base pairs scattered across the genome. CHG and CHH DMRs tended to overlap with transposable elements. CG DMRs tended to overlap with gene coding regions, many of which were previously found to be differentially expressed.

CONCLUSIONS

Genome-wide increases in methylome variation suggest that parental conditions can increase epigenetic diversity in response to stress. Additionally, the potential association between CG DMRs and differentially expressed genes supports the hypothesis that differential methylation is a mechanistic component of transgenerational plasticity in M. guttatus.

Adaptation to environmental stress at different timescales

Environments are changing rapidly, and to cope with these changes, organisms have to adapt. Adaptation can take many shapes and occur at different speeds, depending on the type of response, the trait, the population, and the environmental conditions. The biodiversity crisis that we are currently facing illustrates that numerous species and populations are not capable of adapting with sufficient speed to ongoing environmental changes. Here, we discuss current knowledge on the ability of animals and plants to adapt to environmental stress on different timescales, mainly focusing on thermal stress and ectotherms. We discuss within-generation responses that can be fast and induced within minutes or hours, evolutionary adaptations that are often slow and take several generations, and mechanisms that lay somewhere in between and that include epigenetic transgenerational effects. To understand and predict the impacts of environmental change and stress on biodiversity, we suggest that future studies should (1) have an increased focus on understanding the type and speed of responses to fast environmental changes; (2) focus on the importance of environmental fluctuations and the predictability of environmental conditions on adaptive capabilities, preferably in field studies encompassing several fitness components; and (3) look at ecosystem responses to environmental stress and their resilience when disturbed.

Transgenerational plasticity in Silene vulgaris in response to three types of stress

The environment experienced by plants can influence the phenotype of their offspring. Such transgenerational plasticity can be adaptive when it results in higher fitness of the offspring under conditions correlated with those experienced by the mother plant. However, it has rarely been tested if such anticipatory parental effects may be induced with different environments. We grew clonal replicates of Silene vulgaris under control conditions and three types of stress (nutrient deficiency, copper addition and drought), which are known from natural populations of the species. We then subjected offspring from differently treated mother plants to each of the different stress treatments to analyse the influence of maternal and offspring environment on performance and several functional traits. Current stress treatments strongly influenced biomass and functional traits of the plants, mostly in line with responses predicted by the theory of functional equilibrium. Plant performance was also influenced by maternal stress treatments, and some effects independent of initial size differences remained until harvest. In particular, stressed mothers produced offspring of higher fitness than control plants. However, there was no evidence for treatment-specific adaptive transgenerational plasticity, as offspring from a mother plant that had grown in a specific environment did not grow better in that environment than other plants. Our results indicate that the maternal environment may affect offspring traits and performance, but also that this transgenerational plasticity is not necessarily adaptive.

Parental and embryonic experiences with predation risk affect prey offspring behaviour and performance

Because phenotypic plasticity can operate both within and between generations, phenotypic outcomes are often shaped by a complex history of environmental signals. For example, parental and embryonic experiences with predation risk can both independently and interactively influence prey offspring traits early in their life. Parental and embryonic risk experiences can also independently shape offspring phenotypes throughout an offspring's ontogeny, but the persistence of their interactive effects throughout offspring ontogeny is unknown. We examined the effects of parental and embryonic experiences with predation risk on the response of 1-year-old prey (the carnivorous snail, Nucella lapillus) offspring to current predation risk. We found that parental and embryonic risk experiences had largely independent effects on offspring performance and that these effects were context dependent. Parental experience with risk had strong impacts on multiple offspring traits in the presence of current risk that generally improved offspring performance under risk, but embryonic risk experience had relatively weaker effects and only operated in the absence of current risk to reduce offspring growth. These results illustrate that past environmental experiences can dynamically shape organism phenotypes across ontogeny and that attention to these effects is key to a better understanding of predator/prey dynamics in natural systems.