Within-plant heterogeneity in fecundity and herbivory induced by localized DNA hypomethylation in the perennial herb Helleborus foetidus

PREMISE

Phenotypic heterogeneity of reiterated, homologous structures produced by individual plants has ecological consequences for plants and their animal consumers. This paper examines experimentally the epigenetic mosaicism hypothesis, which postulates that within-plant variation in traits of reiterated structures may partly arise from different parts of the same genetic individual differing in patterns or extent of genomic DNA methylation.

METHODS

Leaves of paired ramets borne by field-growing Helleborus foetidus plants were infiltrated periodically over the entire flowering period with either a water solution of the demethylating agent zebularine or just water as the control. The effects of the zebularine treatment were assessed by quantifying genome-wide DNA cytosine methylation in leaves and monitoring inflorescence growth and flower production, number of ovules per flower, pollination success, fruit set, seed set, seed size, and distribution of sap-feeding insects.

RESULTS

Genomic DNA from leaves in zebularine-treated ramets was significantly less methylated than DNA from leaves in control ones. Inflorescences in treated ramets grew smaller and produced fewer flowers, with fewer ovules and lower follicle and seed set, but did not differ from inflorescences in untreated ramets in pollination success or seed size. The zebularine treatment influenced the within-plant distribution of sap-feeding insects.

CONCLUSIONS

Experimental manipulation of genomic DNA methylation level in leaves of wild-growing H. foetidus plants induced considerable within-plant heterogeneity in phenotypic (inflorescences, flowers, fecundity) and ecologically relevant traits (herbivore distribution), which supports the hypothesis that epigenetic mosaicism may partly account for within-plant variation.

Pharmacology and psychiatry at the origins of Greek medicine: The myth of Melampus and the madness of the Proetides

Melampus is a seer-healer of Greek myth attributed with having healed the young princesses of Argos of madness. Analysis of this legend and its sources sheds light on the early stages of the "medicalizing" shift in the history of ancient Greek medicine. Retrospective psychological diagnosis suggests that the descriptions of the youths' madness rose from actual observation of behavioral and mental disorders. Melampus is credited with having healed them by administering hellebore. Pharmacological analysis of botanical specimens proves that Helleborus niger features actual neurological properties effective in the treatment of mental disorders. The discussion aims at examining the rational aspects of the treatment of mental conditions in Greco-Roman antiquity.

The Hellebore, the Plant beloved by the Greeks: the Reasons behind a Myth

This article surveys the characteristics and therapeutic use of black and white hellebore, the beloved plants of the Greeks. It tries to assess the reasons for their possible correct or disastrous use, according to the Greek texts, focusing on some evidence of drug experiments on tolerance to poisons, performed before Mithidrates Eupator's pioneering approach to toxicology. It also draws on new insights into promising remedies obtained from Helleborus provided by phytochemically active compounds.

Individual variation in size and fecundity is correlated with differences in global DNA cytosine methylation in the perennial herb Helleborus foetidus (Ranunculaceae)

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PREMISE OF THE STUDY

Few studies have examined how epigenetic modifications of DNA may influence individual plant phenotypes and ecological processes in wild plant populations. We investigated natural variation in global DNA cytosine methylation and its phenotypic correlates in the perennial herb Helleborus foetidus.•

METHODS

We focused specifically on individual differences in size- and fecundity-related traits and used HPLC to quantify percentage of total cytosines in the genome of young full-grown leaves that were methylated.•

KEY RESULTS

About one third of all cytosines in H. foetidus genome were methylated. Methylation level differed significantly among individual plants (range = 26.4-36.6%; n = 60 plants), and this variation was significantly related to most size- and fecundity-related traits considered. Relatively hypomethylated plants bore more vegetative, reproductive, and total ramets, produced more flowers, larger inflorescences and more seed-bearing follicles, and their ramets remained vegetative for fewer years before reproducing sexually, than relatively hypermethylated ones. Taken together, results revealed that individual differences in size and reproductive output were inversely related to global cytosine methylation.•

CONCLUSIONS

These results confirm, in a natural scenario, the association between DNA methylation and size- and fecundity-related traits that was previously found by experimental studies. Variations in global cytosine methylation were predictably related to individual differences in sexual reproduction through significant effects on flower and fruit production, which might ultimately influence patterns of selection and population dynamics in this species. This study provides novel insights on the potential ecological significance of epigenetic heterogeneity in wild plant populations.

Evaluation of reproductive barriers and realisation of interspecific hybridisations depending on genetic distances between species in the genus Helleborus

The genus Helleborus comprises 22 species, which are allocated to six sections. H. x hybridus and H. niger, which belong to different Helleborus sections, are economically important ornamentals. Several other species with minor impact exhibit interesting features, e.g. flower size, flower colour, foliage, scent and disease resistance, which should be introgressed into H. x hybridus or H. niger through interspecific hybridisation. The aims of this study were to investigate whether and which kind of hybridisation barriers occur in crosses between Helleborus species and if they differ in their manifestations, depending on the genetic distance of the respective partners. In order to obtain interspecific hybrids despite crossing barriers, a method to overcome these barriers should be developed. Crossing barriers in Helleborus were localised as predominantly post-zygotic according to in situ pollen tube staining with aniline blue. For certain crosses, pre-zygotic barriers could also be assumed, but pollen tube growth was not totally inhibited. Therefore, embryo rescue techniques via ovule culture were established to overcome the post-zygotic barriers. Ovules were isolated from maternal plants 5-7 weeks after pollination in most cases and then cultured in vitro. Overall, 219 hybrids were successfully obtained, of which 16 were derived from inter-sectional crosses. Hybrids were verified by flow cytometry and/or by molecular DNA markers.

Synchrony between fruit maturation and effective dispersers' foraging activity increases seed protection against seed predators

The evolution of pollination and seed dispersal mutualisms is conditioned by the spatial and temporal co-occurrence of animals and plants. In the present study we explore the timing of seed release of a myrmecochorous plant (Helleborus foetidus) and ant activity in two populations in southern Spain during 2 consecutive years. The results indicate that fruit dehiscence and seed shedding occur mostly in the morning and correspond to the period of maximum foraging activity of the most effective ant dispersers. By contrast, ant species that do not transport seeds and/or that do not abound near the plants are active either before or after H. foetidus diaspores are released. Experimental analysis of diet preference for three kinds of food shows that effective ant dispersers are mostly scavengers that readily feed on insect corpses and sugars. Artificial seed depots suggest that seeds deposited on the ground out of the natural daily time window of diaspore releasing are not removed by ants and suffer strong predation by nocturnal rodents Apodemus sylvaticus. Nevertheless, important inter-annual variations in rodent populations cast doubts on their real importance as selection agents. We argue that traits allowing synchrony between seed presentation and effective partners may constitute a crucial pre-adaptation for the evolution of plant-animal mutualisms involving numerous animal partners.

Geographic variations in seed dispersal by ants: are plant and seed traits decisive?

The effect of local ant species on the dispersal success of a myrmecochorous plant, Helleborus foetidus, was analyzed in two populations of the Iberian Peninsula (Caurel and Cazorla, respectively). The contribution of the various local ant species to dispersal was very unequal. While 5 and 19 ant taxa visited the plants of Caurel and Cazorla, respectively, most removal activity (67 and 80%) was performed by two species only (Formica lugubris and Camponotus cruentatus, respectively). Visits by dispersers were also unequally distributed between neighboring plants. While some plants were always visited during the period of seed release, others were never visited. A regression model indicated that this pattern might be explained by two plant traits: ants preferred to visit plants that released more seeds and whose elaiosomes were richer in oleic acid. Although it has long been known that this compound triggers removal by ants, it is the first demonstration that quantitative variations in elaiosome traits contribute to variation in dispersal success. Finally, other variables being equal, morphological traits (seed size, elaiosome size, and elaiosome/seed size ratio) did not affect ant behavior. Although myrmecochory has long been considered a diffuse interaction, our results support the idea that, at local scale, a limited number of ant species may be decisive to its evolution.

The geographic mosaic in predispersal interactions and selection on Helleborus foetidus (Ranunculaceae)

We examine the hierarchical geographic structure of the interaction between a plant, Helleborus foetidus, and its floral herbivores and pollinators (interactors). Six populations from three distant regions of the Iberian Peninsula were used to examine intra- and inter-regional variation in plant traits, interactors and plant fecundity, and to compare, through selection gradient and path analyses, which traits were under selection, and which interactors were responsible for differential selection. Geographic and temporal congruency in interactor-mediated selection was further tested using a recent analytical approach based on multi-group comparison in Structural Equation Models. Most plant traits, interactors and fecundity differed among regions but not between populations. Similarly, the identity of the traits under selection, the selection gradients (strength and/or the direction of the selection) and the path coefficients (identifying the ecological basis for selection) varied inter- but not intra-regionally. Results show a selection mosaic at the broad scale and, for some traits, a link of differential selection to trait differentiation.

Plant traits, environmental factors, and pollinator visitation in winter-flowering Helleborus foetidus (Ranunculaceae)

BACKGROUND AND AIMS

This study examined the effect of plant traits and environmental factors on pollinator visitation in the winter-flowering Helleborus foetidus (Ranunculaceae) in three distant regions in the Iberian Peninsula.

METHODS

Geographical variation in floral visitor assemblage, plant traits and environmental factors were analysed during the flowering season.

KEY RESULTS

Differences were found in all plant traits measured (number of open flowers, flower size, number of stamens per flower, and number of nectaries) both within and among regions, and differences among regions in all the environmental factors considered (air temperature, exposure to sunlight, canopy cover, and distance to the nearest neighbour). Differences were also found among regions in the probability that plants would be visited by pollinators.

CONCLUSIONS

The results show that, although floral display (i.e. number of open flowers on a plant on a given day) consistently explained among-plant differences in visitation rate in all regions, visitation rate was not significantly affected by any other biological or environmental variable. In Helleborus foetidus, then, 'how' the plant is would seem to be more important than 'where' is it.