High Small-Scale Variation of Leaf Traits And Their Plasticity Within And Among Genotypes of A Clonal Species

Genetic variation of plant traits and their phenotypic plasticity are two supplementary ways of plant adaptation to temporarily fluctuating and spatially heterogeneous environmental conditions. Genetic variability and plasticity of leaf traits have been studied extensively as important indicators of the plant survival. In the case of clonal species with a patchy local distribution of clonal individuals, it would be important to investigate leaf traits at a small spatial scale. Here, small-scale variability of leaf traits and their plasticity within and among clonally spread genotypes in small 2 x 2 m plots was examined on the example of the clonal legume Trifolium alpestre. Seven leaf traits, leaflet length, area, width, fresh and dry weights, dry matter content (LDMC), and specific leaf area (SLA), were measured for ramets of various clonal genotypes sampled from five natural populations of T. alpestre. High variation of leaf traits and their plasticity was detected among the individual ramets of genotypes in 2 x 2 m plots of within the same population, as well as differential variation among the genotypes from different populations. The extent of variation in leaf traits and plasticity was found to be specific for the particular trait, genotype and site. The observed high variation of leaf traits and their plasticity within and among the clonally spread genotypes in local sites of populations is attributed to their differential combined response on the small-scale heterogeneity in the habitat conditions and genetic factors. High variation of leaf traits and their plasticity allows plants effectively respond to spatiotemporally fluctuating environmental conditions.

Sticking around: plant persistence strategies on edaphic islands

1. Species extinction risk at local scales can be partially offset by strategies promoting in-situ persistence. We explored how persistence-related traits of clonal and non-clonal plants in temperate dry grasslands respond intra- and interspecifically to variation in environmental conditions (soil, climate) and insularity. 2. We focused on edaphic island specialist species, hypothesizing that plants experiencing harsh soil environments and strong insularity are distinguished by traits supporting enhanced persistence, such as small stature, long lifespan and resource-conservative strategies. We used linear mixed-effect models and bivariate ordinary least squares linear models to explore the response of species triats to environmental and biogeographic predictors. 3. We found general support for this hypothesis. Soil properties and insularity emerged as the most important drivers of trait patterns. However, clonal species showed more consistent responses to variation in environmental conditions and insularity than non-clonal plants, which were characterized by distinct species-specific responses. 4. Soil properties and insularity confirmed their major role in shaping the persistence strategies of edaphic island plant species. These drivers may exert their effect on specific functions (e.g. belowground resource conservation captured by BDMC). Additionally, we unambiguously identified that clonal species had different persistence strategies than non-clonal ones.

Clonal versus non-clonal milkweeds (Asclepias spp.) respond differently to stem damage, affecting oviposition by monarch butterflies

Background Oviposition decisions are critical to the fitness of herbivorous insects and are often impacted by the availability and condition of host plants. Monarch butterflies (Danaus plexippus) rely on milkweeds (Asclepias spp.) for egg-laying and as food for larvae. Previous work has shown that monarchs prefer to oviposit on recently regrown plant tissues (after removal of above-ground biomass) while larvae grow poorly on plants previously damaged by insects. We hypothesized that these effects may depend on the life-history strategy of plants, as clonal and non-clonal milkweed species differ in resource allocation and defense strategies. Methodology/Principal Findings We first confirmed butterfly preference for regrown tissue in a field survey of paired mowed and unmowed plots of the common milkweed A. syriaca. We then experimentally studied the effects of plant damage (comparing undamaged controls to plants clipped and regrown, or damaged by insects) on oviposition choice, larval performance, and leaf quality of two closely related clonal and non-clonal species pairs: (1) A. syriaca and A. tuberosa, and (2) A. verticillata and A. incarnata. Clonal and non-clonal species displayed different responses to plant damage, impacting the proportions of eggs laid on plants. Clonal species had similar mean proportions of eggs on regrown and control plants (≈35–40% each), but fewer on insect-damaged plants (≈20%). Meanwhile non-clonal species had similar oviposition on insect-damaged and control plants (20–30% each) but more eggs on regrown plants (40–60%). Trait analyses showed reduced defenses in regrown plants and we found some evidence, although variable, for negative effects of insect damage on subsequent larval performance. Conclusions/Significance Overall, non-clonal species are more susceptible and preferred by monarch butterflies following clipping, while clonal species show tolerance to clipping and induced defense to insect herbivory. These results have implications for monarch conservation strategies that involve milkweed habitat management by mowing. More generally, plant life-history may mediate growth and defense strategies, explaining species-level variation in responses to different types of damage.

Genomic evolution of Neisseria gonorrhoeae since the preantibiotic era (1928–2013): antimicrobial use/misuse selects for resistance and drives evolution

Background Multidrug-resistant Neisseria gonorrhoeae strains are prevalent, threatening gonorrhoea treatment globally, and understanding of emergence, evolution, and spread of antimicrobial resistance (AMR) in gonococci remains limited. We describe the genomic evolution of gonococci and their AMR, related to the introduction of antimicrobial therapies, examining isolates from 1928 (preantibiotic era) to 2013 in Denmark. This is, to our knowledge, the oldest gonococcal collection globally. Methods Lyophilised isolates were revived and examined using Etest (18 antimicrobials) and whole-genome sequencing (WGS). Quality-assured genome sequences were obtained for 191 viable and 40 non-viable isolates and analysed with multiple phylogenomic approaches. Results Gonococcal AMR, including an accumulation of multiple AMR determinants, started to emerge particularly in the 1950s–1970s. By the twenty-first century, resistance to most antimicrobials was common. Despite that some AMR determinants affect many physiological functions and fitness, AMR determinants were mainly selected by the use/misuse of gonorrhoea therapeutic antimicrobials. Most AMR developed in strains belonging to one multidrug-resistant (MDR) clade with close to three times higher genomic mutation rate. Modern N. gonorrhoeae was inferred to have emerged in the late-1500s and its genome became increasingly conserved over time. Conclusions WGS of gonococci from 1928 to 2013 showed that no AMR determinants, except penB, were in detectable frequency before the introduction of gonorrhoea therapeutic antimicrobials. The modern gonococcus is substantially younger than previously hypothesized and has been evolving into a more clonal species, driven by the use/misuse of antimicrobials. The MDR gonococcal clade should be further investigated for early detection of strains with predispositions to develop and maintain MDR and for initiation of public health interventions.

Somatic genetic drift and multi-level selection in modular species

Cells in multicellular organisms are genetically heterogeneous owing to somatic mutations. The accumulation of somatic genetic variation in species undergoing asexual (or clonal) reproduction (termed modular species) may lead to phenotypic heterogeneity among modules. However, abundance and dynamics of somatic genetic variation under clonal growth, a widespread life history in nature, remain poorly understood. Here we show that branching events in a seagrass clone or genet leads to population bottlenecks at the cellular level and hence the evolution of genetically differentiated modules. Studying inter-module somatic genetic variation, we uncovered thousands of SNPs that segregated among modules. The strength of purifying selection on mosaic genetic variation was greater at the intra-module comparing with the inter-module level. Our study provides evidence for the operation of selection at multiple levels, of cell population and modules. Somatic genetic drift leads to the emergence of genetically unique modules; hence, modules in long-lived clonal species constitute an appropriate elementary level of selection and individuality.

Differences in physiological integration between invasive and noninvasive introduced clonal species of Carpobrotus

Aims Clonal growth is associated with invasiveness in introduced plant species, but few studies have compared invasive and noninvasive introduced clonal species to investigate which clonal traits may underlie invasiveness. To test the hypothesis that greater capacity to increase clonal growth via physiological integration of connected ramets increases invasiveness in clonal plants, we compared the effects of severing connections on accumulation of mass in the two species of the creeping, succulent, perennial, herbaceous genus Carpobrotus that have been introduced on sand dunes along the Pacific Coast of northern California, the highly invasive species Carpobrotus edulis and the co-occurring, noninvasive species Carpobrotus chilensis. Methods Pairs of ramets from four mixed populations of the species from California were grown in a common garden for 3 months with and without severing the stem connecting the ramets. To simulate the effect of clones on soils in natural populations, the older ramet was grown in sand amended with potting compost and the younger in sand alone. Important Findings Severance decreased net growth in mass by ~60% in C. edulis and ~100% in C. chilensis, due mainly to the negative effect of severance on the shoot mass of the younger ramet within a pair. Contrary to the hypothesis, this suggests that physiological integration increases growth more in the less invasive species. However, severance also decreased allocation of mass to roots in the older ramet and increased it in the younger ramet in a pair, and the effect on the younger ramet was about twice as great in C. edulis as in C. chilensis. This indicates that the more invasive species shows greater phenotypic plasticity in response to physiological integration, in particular greater capacity for division of labor. This could contribute to greater long-term growth and suggests that the division of labor may be a trait that underlies the association between clonal growth and invasiveness in plants.