Interspecific Competitive Ability Research Articles

Development and application of the fungal plant pathogen Colletotrichum shisoi to control invasive Perilla frutescens

Inadvertently introduced plant pathogens that infect invasive plant species might be effective weed biological control agents if developed for redistribution or augmentation of naturally occurring populations. Colletotrichum shisoi is likely an inadvertent introduction to the United States where it causes disease on invasive perilla mint (Perilla frutescens). This study reports on the development and application of C. shisoi as a biological control agent. The effects of dew period on infection probability and of inoculum concentration on perilla biomass production were determined to identify a threshold dose and dew period required for effective biological control activity. Under controlled conditions, application of the pathogen reduced perilla biomass, flower production, and interspecific competitive ability. In a replicated field trial, both the introduction and augmentation of C. shisoi populations caused high perilla mortality and moderate changes in plant community composition over one growing season. Additionally, a series of experiments were performed to evaluate methods for the production and preservation of C. shisoi spores. Overall, the pathogen was found to be an effective antagonist of perilla mint when applied inundatively under appropriate conditions. It may be possible to produce the pathogen in mass for redistribution across the invaded range of perilla in North America, but further research is needed for adequate preservation of inoculum during transport and application.

Temperature and hypoxia‐driven shifts in Daphnia interspecific competition

AbstractPrevious research has shown that elevated temperature and environmental hypoxia are associated with a reduced representation of larger‐bodied species in communities of ectotherms, suggesting their competitive disadvantage resulting from increased oxygen demands and limited oxygen availability. To investigate this, we conducted a comparative analysis of two pairs of competing zooplankton species: Daphnia galeata (smaller‐bodied) and Daphnia pulex (larger‐bodied), as well as D. pulex (smaller‐bodied) and Daphnia magna (larger‐bodied). We monitored their population dynamics under different oxygen concentrations and temperatures, and additionally measured hemoglobin concentration in the latter pair. Contrary to expectations, the results demonstrated that the larger‐bodied species outcompeted the smaller‐bodied ones in all experimental treatments involving the first pair of species. In the second pair, elevated temperature favored the smaller‐bodied species, while environmental hypoxia had the opposite effect. The competitive advantage of D. pulex under elevated temperature likely stemmed from their ability to allocate energy from somatic growth to reproduction, as indicated by the increased number of reproducing females. Conversely, the competitive advantage of D. magna under environmental hypoxia may be attributed to their ability to reallocate energy from reproduction to somatic growth, as indicated by lower reproductive effort and greater plasticity in hemoglobin production. These findings indicate that elevated temperature and hypoxia can independently and jointly influence interspecific competitive abilities by impacting the pace of life. However, the numerical dominance of smaller‐sized species in warm and hypoxic zooplankton communities cannot be explained by their enhanced competitive abilities resulting from a more favorable oxygen supply demand balance.

Oviposition fluids from adult wasps mediate interspecific competition between parasitoid larvae

Abstract Parasitoid wasp larvae engage in intense interspecific competition when sharing a host insect, with lethal consequences for the losers. Larval parasitoid competition is generally thought to be resolved by physical traits, such as enlarged mandibles. Although solitary parasitoid larvae are typically superior competitors against gregarious larvae, such physical traits are unlikely to be effective against large numbers of competitors. Larval competition may instead be mediated by maternal factors that increase the survival of offspring facing interspecific competition, thus increasing parental fitness. When laying eggs inside a host, many female parasitoids also inject oviposition fluids that are known to suppress host immune responses, permitting successful offspring development. We explored whether the oviposition fluids of two wasp species in the genus Cotesia (Cotesia rubecula, a strong competitor that almost always wins interspecific competition against a weaker competitor, Cotesia glomerata) might also represent maternal factors that improve the interspecific competitive ability of their offspring. We demonstrate that injections of both venom and calyx fluid from C. rubecula can inhibit egg hatching and larval development of C. glomerata. Venom from C. rubecula decreased C. glomerata egg development by 2.7 times, and calyx fluid injections caused deformities in 23% of developing C. glomerata. In contrast, reciprocal injections of the oviposition fluids from C. glomerata did not inhibit the development of C. rubecula. Our results show that maternal factors can improve the interspecific competitive ability of parasitoid larvae, challenging the previous assumptions that larval competition was resolved primarily through physical combat or larval secretions.

Growth of the invasive Navua sedge (Cyperus aromaticus) under competitive interaction with pasture species and simulated grazing conditions: Implication for management

AbstractNavua sedge (Cyperus aromaticus), a perennial monocot plant native to tropical Africa, is a major weed in pasture and cropping areas in the wet tropical regions of Australia and South Pacific countries. In grazing pasture lands, rapid growth and reproduction of unpalatable Navua sedge leads to displacement of co‐occurring pasture species and depletion of livestock carrying capacity and production. Understanding the interspecific competitive ability of Navua sedge with co‐occurring desirable grasses and in response to varying ecological scenarios (e.g., grazing and plant density) is critical for the management of the weed in pasture situations. In a glasshouse setting, two co‐occurring pasture species—humidicola (Urochloa humidicola) and Rhodes grass (Chloris gayana) were grown with Navua sedge, in pots using a replacement series model. For each Navua sedge weed–pasture species pair, the experimental setup comprised of four ratios in two densities under simulated grazing and nongrazing conditions of the pasture grasses. Navua sedge growth and reproduction was highest when it grew as a monoculture or when co‐occurring pastures were exposed to simulated grazing as this action, reduced the competitiveness of the pasture grasses. Overall and using biomass gained, tiller production and relative yield as indices of growth dynamics, Rhodes grass was more competitive against Navua sedge than humidicola in both grazed and nongrazed conditions especially under high plant density. These results suggest the potential to include competitive pastures in integrated management strategies for Navua sedge, but species selection and grazing practices may influence the effectiveness of this approach.

The effects ofEpichloëendophytes on the growth and competitiveness ofAchnatherum sibiricumare mediated by soil microbe diversity

AbstractMany grasses are infected by systemic fungal endophytes that occur in aboveground plant tissues. Both aboveground endophytic fungi and belowground soil microbes can influence plant growth, but studies on their simultaneous effects on plant growth and competitiveness are limited. This study aims to investigate whether the role of aboveground endophytic fungi in the growth and competitive ability of the host grasses was influenced by soil microbes. In this study, we used Epichloë endophyte-infected and endophyte-free Achnatherum sibiricum as plant materials. A wet sieving method was adopted to obtain microbial inocula with different diversities (com, combined microbe fraction, high diversity; sm, small microbe fraction, low diversity). A three-factor randomized block design was used. The first factor was the endophyte infection status of A. sibiricum. The second factor was the microbial composition of the soil inocula. The third factor was the planting type. Growth and competitive characters were measured after 16 weeks. The results showed that a soil microbe inoculation was detrimental to the growth of A. sibiricum. Epichloë endophytes significantly mitigated the inhibitory effect of soil microbes on A. sibiricum planted alone. When A. sibiricum was planted with Stipa grandis, there was a significant interaction between Epichloë endophytes and soil microbes on the interspecific competition of A. sibiricum. When inoculated with small microbial community fraction, Epichloë endophytes significantly improved the interspecific competitive ability of host plants. When inoculated with combined microbial community fraction, however, Epichloë endophytes had no significant effect on host competition. The results showed that the interaction between Epichloë endophytes and soil microbes contributed more to the interspecific competitive ability than either Epichloë endophytes or soil microbes alone.

克隆和有性亲体效应及其调控机制

PDF HTML阅读 XML下载 导出引用 引用提醒 克隆和有性亲体效应及其调控机制 DOI: 10.5846/stxb202107211968 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 中央高校基本科研业务费专项资金项目（2021ZY90）；国家自然科学基金项目（32071525，32071527） Clonal and sexual parental effects and their mechanisms Author: Affiliation: Fund Project: the Fundamental Research Funds for the Central Universities (2021ZY90), National Natural Science Foundation of China (32071525; 32071527) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:植物表型受自身基因型、所处环境及其亲体所经历环境的共同影响；其中，亲体环境对子代表型的影响被称为亲体效应。亲体效应不仅可通过有性繁殖产生的种子传递给后代（即有性亲体效应），也可以通过克隆生长等无性繁殖产生的分株传递给后代（即克隆亲体效应）。亲体效应对植物种群，特别是对有性繁殖受限、缺乏遗传变异的克隆植物种群的长期进化可能发挥着极其重要的作用，因此，对亲体效应研究进展的梳理非常必要。对克隆亲体效应和有性亲体效应的内涵进行了阐释，并论述了克隆和有性亲体效应对子代表型、适合度、种内/种间竞争能力以及种群/群落结构和功能的潜在影响；阐述了亲体效应的潜在调控机制，包括供给机制、代谢物质调控机制、表观遗传机制等；论述了克隆亲体效应在克隆植物适应进化中的作用。未来可以就克隆亲体效应的遗传稳定性及其对克隆生活史性状变异的贡献程度，以及克隆和有性亲体效应引起的表型多样性对种内/种间关系、种群/群落多样性及生态系统结构、功能和稳定性的影响开展深入研究。 Abstract:The phenotype of a plant can be jointly determined by its genotype, the environmental condition experienced by itself and the environmental condition(s) experienced by its parents. The latter, i.e., the impacts of parental environment conditions on offspring phenotypes, are referred to as parental effects, maternal effects or paternal effects. Because parental effects reflect the response of offspring phenotypes to environment conditions across generations, it is also named transgenerational plasticity. Parental effects may have played an important role in the long-term evolution of plant populations, especially for those with limited sexual reproduction and thus low genetic variation. In this paper, we reviewed the research progresses of parental effects and pointed out the future research directions. We explicitly defined two types of parental effects, i.e., clonal parental effects and sexual parental effects. The former refer to parental effects that are transmitted to offspring through ramets produced by clonal growth and other asexual reproduction, while the latter refer to those that are transmitted to offspring through seeds produced by sexual reproduction. While sexual parental effects have long been recognized, clonal parental effects are called for attention only in recent years. Both sexual and clonal parental effects generally enhance offspring performance, but sometimes also show neutral or even negative effects, in response to abiotic or biotic stresses. For clonal parental effects, a few studies have investigated that the impacts on growth and physiological traits of clonal offspring strongly depend on offspring environment and levels of plants (i.e., an individual offspring or all offspring of a parent); however, such impacts on exclusive life-history traits of clonal offspring, such as clonal growth, clonal integration, clonal plasticity and intraclonal labor division, are still unclear. The potential mechanisms of parental effects are the provisioning mechanism, metabolic regulation mechanism and epigenetic mechanism. In natural conditions, these three mechanisms often jointly act to affect offspring phenotypes, and their effects cannot be strictly separated from each other. Although a large body of studies have examined parental effects at individual level, there are still limited studies at population level and virtually none at community level. As parental effects can influence offspring phenotypes, they can influence their intra- and inter-specific competitive ability, which may further impact population structure and dynamics and community function and stability. Therefore, future studies of parental effects should test the impact of phenotypic differences/diversity induced by parental effects on intra-/inter-specific relationships, population structure and dynamics and community function (e.g., productivity) and stability. The epigenetic mechanism underlying these population- and community-level parental effects should also be explicitly evaluated. 参考文献 相似文献 引证文献

Shift in competitive ability mediated by soil biota in an invasive plant.

Understanding the shifts in competitive ability and its driving forces is key to predict the future of plant invasion. Changes in the competition environment and soil biota are two selective forces that impose remarkable influences on competitive ability. By far, evidence of the interactive effects of competition environment and soil biota on competitive ability of invasive species is rare. Here, we investigated their interactive effects using an invasive perennial vine, Mikania micrantha. The competitive performance of seven M. micrantha populations varying in their conspecific and heterospecific abundance were monitored in a greenhouse experiment, by manipulating soil biota (live and sterilized) and competition conditions (competition‐free, intraspecific, and interspecific competition). Our results showed that with increasing conspecific abundance and decreasing heterospecific abundance, (1) M. micrantha increased intraspecific competition tolerance and intra‐ vs. interspecific competitive ability but decreased interspecific competition tolerance; (2) M. micrantha increased tolerance of the negative soil biota effect; and (3) interspecific competition tolerance of M. micrantha was increasingly suppressed by the presence of soil biota, but intraspecific competition tolerance was less affected. These results highlight the importance of the soil biota effect on the evolution of competitive ability during the invasion process. To better control M. micrantha invasion, our results imply that introduction of competition‐tolerant native plants that align with conservation priorities may be effective where M. micrantha populations are long‐established and inferior in inter‐ vs. intraspecific competitive ability, whereas eradication may be effective where populations are newly invaded and fast‐growing.

Competitive ability of native and alien plants: effects of residence time and invasion status

Competition is commonly thought to underlie the impact of plant invasions. However, competitive effects of aliens and competitive response of natives may also change over time. Indeed, as with time, the novelty of an invader decreases, the accumulated eco-evolutionary experience of resident species may eventually limit invasion success. We aimed to gain insights on whether directional changes in biotic interactions over time or more general differences between natives and aliens, for instance, resulting from an introduction bias, are relevant in determining competitive ability. We conducted a pairwise competition experiment in a target-neighbour design, using 47 Asteraceae species with residence times between 8 years-12,000 years in Germany. We first tested whether there are differences in performance in intraspecific competition amongst invasion status groups, that is casual and established neophytes, archaeophytes or native species. We then evaluated whether competitive response and effects depend on residence time or invasion status. Lastly, we assessed whether competitive effects influence range sizes. We found only limited evidence that native target species tolerate neighbours with longer potential co-existence times better, whereas differences in competitive ability were mostly better explained by invasion status than residence time. Although casual neophytes produced most biomass in intraspecific competition, they had the weakest per-capita competitive effects on natives. Notably, we did not find differences between established neophytes and natives, both of which ranked highest in interspecific competitive ability. This lack of differences might be explained by a biased selection of highly invasive or rare native species in previous studies or because invasion success may result from mechanisms other than interspecific competitive superiority. Accordingly, interspecific per-capita competitive effects did not influence range sizes. Further studies across a broader range of environmental conditions, involving other biotic interactions that indirectly influence plant-plant interactions, may clarify when eco-evolutionary adaptations to new invaders are a relevant mechanism.

Individual growth, competitive ability and stand-level biomass production of invasive Sorghum halepense populations on Hainan island, China

Abstract Aims Sorghum halepense is a perennial invasive weed causing great harm worldwide, including some regions on Hainan island. In this study, we compared the performance between plants from outbreaking (dense stands covering large areas) and those from non-outbreaking (less dense stands covering smaller areas) populations. We also tested the hypothesis that plants with greater intraspecific competitive ability will have a lower stand biomass when grown under high-density conditions. Methods We grew plants of S. halepense individually, with an intraspecific competitor, with two interspecific competitors and with three or six plants from the same population per pot, and tested whether outbreaking and non-outbreaking populations differed in their performance. We also tested whether stand biomass (i.e. total biomass when three or six plants were grown together) was related to total biomass of individuals grown alone, and intra- or interspecific competitive ability. Important Findings Outbreaking and non-outbreaking populations of S. halepense differed in their biomass when individuals were grown alone, but not when grown in competition or when three or six plants from the same population were grown together. Across populations, biomass of individuals grown alone was negatively correlated with intra- and interspecific competitive ability, indicating that there is a trade-off between individual growth and competitive ability. Stand-level biomass was not related to total biomass of individuals grown alone, and intra- or interspecific competitive ability, indicating that low biomass when grown alone and high competitive ability may not reduce the performance of S. halepense when grown in dense monocultural stands.

Eco-Evolutionary Feedbacks and the Maintenance of Metacommunity Diversity in a Changing Environment.

The presence and strength of resource competition can influence how organisms adaptively respond to environmental change. Selection may thus reflect a balance between two forces, adaptation to an environmental optimum and evolution to avoid strong competition. While this phenomenon has previously been explored in the context of single communities, its implications for eco-evolutionary dynamics at the metacommunity scale are largely unknown. We developed a simulation model for the evolution of a quantitative trait that influences both an organism’s carrying capacity and its intra- and interspecific competitive ability. In the model, multiple species inhabit a three-patch landscape, and we investigated the effect of varying the connectivity level among patches, the presence and pace of directional environmental change, and the strength of competition between the species. Our model produced some patterns previously observed in evolving metacommunity models, such as species sorting and community monopolization. However, we found that species sorting was diminished even at low rates of dispersal and was influenced by competition strength, and that monopolization was observed only when environmental change was very rapid. We also detected an eco-evolutionary feedback loop between local phenotypic evolution at one site and competition at another site, which maintains species diversity in some conditions. The existence of a feedback loop maintained by dispersal indicates that eco-evolutionary dynamics in communities operate at a landscape scale.

Differential effect of inter‐ and intraspecific competition on the performance of invasive and native Taraxacum species

AbstractInter‐ and intraspecific competitive abilities are significant determinants of invasive success and the ecological impact of non‐native plants. We tested two major hypotheses on the competitive ability of invasive species using invasive (Taraxacum officinale) and native (T. platycarpum) dandelions: differential interspecific competitive ability between invasive and native species and the kin recognition of invasive species. We collected seeds from two field sites where the two dandelion species occurred nearby. Plants were grown alone, with kin (plants from the same maternal genotype) or strangers (plants from different populations) of the same species, or with different species in a growth chamber, and the performance at the early developmental stage between species and treatments was compared. The invasive dandelions outcompeted the native dandelions when competing against each other, although no difference between species was detected without competition or with intraspecific competition. Populations of native species responded to interspecific competition differently. The effect of kinship on plant performance differed between the tested populations in both species. A population produced more biomass than the other populations when grown with a stranger, and this trend was manifested more in native species. Our results support the hypothesis that invasive plants have better competitive ability than native plants, which potentially contributes to the establishment and the range expansion of T. officinale in the introduced range. Although kin recognition is expected to evolve in invasive species, the competitive ability of populations rather than kinship seems to affect plant growth of invasive T. officinale under intraspecific competition.

Causes of differences in the distribution of the invasive plants Ambrosia artemisiifolia and Ambrosia trifida in the Yili Valley, China.

Ambrosia artemisiifolia and Ambrosia trifida are two species of very harmful and invasive plants of the same genus. However, it remains unclear why A. artemisiifolia is more widely distributed than A. trifida worldwide. Distribution and abundance of these two species were surveyed and measured from 2010 to 2017 in the Yili Valley, Xinjiang, China. Soil temperature and humidity, main companion species, the biological characteristics in farmland ecotone, residential area, roadside and grassland, and water demand of the two species were determined and studied from 2017 to 2018. The area occupied by A. artemisiifolia in the Yili Valley was more extensive than that of A. trifida, while the abundance of A. artemisiifolia in grassland was less than that of A. trifida at eight years after invasion. The interspecific competitive ability of two species was stronger than those of companion species in farmland ecotone, residential, and roadside. In addition, A. trifida had greater interspecific competitive ability than other plant species in grassland. The seed size and seed weight of A. trifida were five times or eight times those of A. artemisiifolia. When comparing the changes under simulated annual precipitation of 840 mm versus 280 mm, the seed yield per m2 of A. trifida decreased from 50,185 to 19, while that of A. artemisiifolia decreased from 15,579 to 530.

Ecological Transitions in Grouping Benefits Explain the Paradox of Environmental Quality and Sociality.

Both benign and harsh environments promote the evolution of sociality. This paradox-societies occur in environments of such contrasting quality-may be explained by the different types of benefits that individuals receive from grouping: resource defense benefits that derive from group-defended critical resources versus collective action benefits that result from social cooperation among group members. Here, we investigate cooperative behavior in the burying beetle Nicrophorus nepalensis along an elevational gradient where environmental quality (climate and competition) varies with altitude. We show that climate (temperature) and competition (both intra- and interspecific) independently and synergistically influence sociality via different grouping benefits that vary along the gradient. At low elevations where interspecific competition for resources is intense, groups gain from the collective action benefit of increased interspecific competitive ability. In contrast, pairs have higher fitness at intermediate elevations where intraspecific competition for resources is greatest because resource defense is the key grouping benefit. However, groups and pairs have similar fitness at high elevations, suggesting that there is no grouping benefit in such physiologically challenging environments. Our results demonstrate that sociality is favored for different reasons under a range of environmental conditions, perhaps explaining why animal societies occur in environments of such contrasting quality.

Effects of Mikania micrantha wilt virus on endogenous hormones and interspecific competitive ability in Mikania micrantha H.B.K.

Effects of Mikania micrantha wilt virus on endogenous hormones and interspecific competitive ability in Mikania micrantha H.B.K.

Elevated nitrogen deposition may advance invasive weed, Solidago canadensis, in calcareous soils

AbstractAimsChange in nitrogen (N) availability regulates phosphorus (P) acquisition and potentially alters the competition among native species and invasive weeds. This study determines how current and projected N deposition affect the growth, the intraspecific and interspecific competitive ability of native and invasive plants in calcareous soils with low P availability.MethodsA controlled greenhouse experiment was conducted using sparingly soluble hydroxyapatite (HAP) to simulate the calcareous soils with low P availability. The growth and competitive intensity between an invasive weed (Solidago canadensis) and a native weed (Pterocypsela laciniata) exposed to two levels of N addition representative of current and future N deposition in China were experimentally determined.Important FindingsP acquisition and the growth of both S. canadensis and P. laciniata growing alone significantly increased with increasing N level. However, the effect of N addition was reduced when intraspecific or interspecific competition existed. N addition altered the competitive relationship between S. canadensis and P. laciniata allowing S. canadensis to out-compete P. laciniata due to variation in P acquisition from HAP. Elevated N deposition might assist the invasion of S. canadensis in the widely distributed calcareous soils under environmental changes.

Effects of endophyte infection on the competitive ability of Achnatherum sibiricum depend on endophyte species and nitrogen availability

Abstract Aims The leaves of almost all terrestrial plant species are colonized by endophytic fungi. Compared to agronomic grasses, which usually harbor few endophytes, native grasses generally possess greater endophyte species diversity. Existing studies examining endophyte effects on natural grasses under competition normally considered the infection status (infected or uninfected), and rarely considered endophyte species. Methods We examined the effects of endophyte infection and of endophyte species on the interspecific competitive ability of a subdominant species, Achnatherum sibiricum, at two nitrogen levels (high nitrogen and low nitrogen). Achnatherum sibiricum plants infected by two different species of endophyte (Epichloë sibirica and E. gansuensis) and uninfected plants were grown in monoculture and binary mixtures with a dominant species, Stipa grandis (six individuals per species for monocultures and three + three individuals of each species in mixtures). Shoot and root biomass, tiller number and total phenolic concentration were measured after 3 months. Moreover, the aggressivity index was calculated to compare the competitive ability of A. sibiricum relative to S. grandis. Important Findings Both E. gansuensis (Eg)- and E. sibirica (Es)-infected A. sibiricum plants showed a greater competitive ability than the uninfected plants under high nitrogen supply, while the opposite result occurred under low nitrogen supply. At high nitrogen levels, Eg plants had a higher tiller number and a greater shoot biomass inhibitory effect on S. grandis than Es plants had when growing in mixture, while Es plants showed better root growth performance than Eg and uninfected plants under mixture conditions at all nitrogen levels. A higher concentration of phenolic compounds in Eg plants than in Es plants might contribute to the higher inhibitory effect of Eg plants on competing plants. Our study indicates that the interaction between endophyte infection and nitrogen availability can alter the competitive ability of the host plant A. sibiricum but that these two endophyte species work in different ways, which may influence the coexistence of A. sibiricum with the dominant species.

Sexual dimorphism in response to herbivory and competition in the dioecious herb Spinacia oleracea

Sexual dimorphism is common in dioecious plant species and is usually attributed to different cost of reproduction associated with male and female functions. Differences in growth and performance between male and female plants may be accentuated under stress, potentially leading to sex-ratio biases and affecting population growth. Environmental stress involves multiple factors that often occur simultaneously. Among different stress combinations that occur in field conditions, competition and herbivory and their interaction are key biotic factors that can affect plant growth and performance. Here, we conducted a glasshouse experiment in Cardiff, UK, using the cultivated spinach, Spinacia oleracea, as a model system to study sexual dimorphism in intra- and inter-specific competitive ability and in response to herbivory by a generalist herbivore Helix aspersa. We found stronger inter- than intra-specific competition: growth (above-ground biomass) and chlorophyll content of male and female plants was reduced when growing with Brassica oleracea, but not when growing with conspecifics. In the absence of herbivory, females growing with same-sex neighbour had greater root biomass than males; whilst herbivory reduced root biomass significantly only in females competing with same sex neighbours. Plant damage caused by herbivores was similar when growing with male or female conspecifics but greater when growing with B. oleracea. Finally, plant damage caused by herbivores did not differ between male and female plants; however, males increased their allocation to roots and reduced their chlorophyll content after damage. Our results showed that sexual dimorphism occurs in S. oleracea, despite being a worldwide crop, selectively bred for its edible leaves. In particular, our results suggest stronger same-sex competition for females and greater tolerance to herbivory in males than in females of S. oleracea..

Intraspecific competition in oat varieties selected for grain yield and milling

Oats likely emerged as part of the weedy grass assemblage in early wheat and barley crops. Some Avena species, such as A. fatua and A. sterilis, evolved into aggressive weeds, and the high interspecific competitive ability of cultivated oats (A. sativa) is valued agronomically to facilitate weed control in rotations. We tested the hypothesis, verified in many crops, that high yield of oats is related to low intraspecific competitive ability. Ten contemporary oat varieties, selected for grain yield and milling attributes, where grown in three environments. Response to competition was calculated as 100 × (Yb – Yc)/Yc, where Y is yield measured in border (b) and centre (c) rows. The same definition was used to calculate response to competition of yield components (biomass, harvest index, grain number, grain weight) and the components of grain number (panicle number and grains per panicle). Yield response to competition was affected by all three sources of variation, i.e. environment, variety and variety × environment interaction. The interaction demonstrates the plasticity of yield response to intraspecific competition; for example, the response to competition of variety Mortlock varied from 9% to 71% among environments. This plasticity in yield response to competition was partially related to variety-dependent responses to competition for biomass and harvest index, number of panicles and number of grains per panicle. We did not find the expected negative association between yield and variety-dependent response to competition. We discuss how this lack of correlation could relate to sampling issues, i.e. a limitation in the range of environments and varieties explored in this study, or reflect a legitimate feature of oat crops arising from early and contemporary selective pressures.

Patterns of species relatedness created by competitive exclusion depend on species niche differences: Evidence from Iberian Atlantic grasslands

It is commonly assumed that closely related species share more similar niches than do distantly related species, thus limiting their ability to coexist and leading to patterns of phylogenetic over-dispersion. On the contrary, recent theoretical developments argue that competitive exclusion may lead to patterns of either over-dispersion, clustering or randomness, depending on the relative importance of niche differences and interspecific competitive ability differences. In this study, we utilized semi-natural grassland communities to test the hypothesis that the pattern of species relatedness generated by competitive exclusion depends on species niche differences. Instead of inferring processes from observed patterns, we experimentally manipulated grassland plots to test the effects of competitive exclusion. We compared grazed plots (in which grazing functioned as an equalizing mechanism and suppressed aboveground competition) with neighbouring plots experimentally excluded from grazing over the course of nine years (in which aboveground competition was not prevented). Weak niche differences between species allowed competitive exclusion to generate phylogenetic clustering, because phylogenetically structured plant canopy height and capacity for lateral spread conferred superior competitive ability to grasses that outcompeted species in all dicot branches. By contrast, moderate niche differences allowed competitive exclusion to result in a random pattern of phylogenetic species assembly, because species niche differences partially counterbalanced competitive exclusion by superior competitors in the grass family. We conclude that patterns of species relatedness created by competitive exclusion in Iberian Atlantic grasslands depend on species niche differences. Competitive exclusion may cause differential patterns of phylogenetic assembly.

Herbivore release drives parallel patterns of evolutionary divergence in invasive plant phenotypes

Summary Herbivory can drive rapid evolution of plant chemical traits mediating defensive and competitive ability. At a geographic scale, plant populations that escape selection from their ancestral herbivores may evolve decreased defence and increased competitiveness. While contrasts between native and invasive populations of plants lend support to this hypothesis, such experiments cannot establish causal links between herbivory and evolved invasive phenotypes. Here, we conducted geographic contrasts, and coupled these with long‐term selection experiments that directly test for evolutionary responses to herbivore exclusion. In common gardens, we contrasted Solidago altissima genotypes that were historically exposed or protected from herbivory across two experimental time‐scales: (i) a natural experiment where plant populations evolved either with native herbivory (in Minnesota and New York) or evolved relatively free from herbivory for ˜100 years in Japan, and (ii) a 12‐year manipulative experiment where plants were either exposed to ambient herbivory or treated with insecticide. In both experiments, plant populations responded to herbivore release by evolving increased production of root allelochemicals and interspecific competitive ability against Poa pratensis. While plant resistance to a beetle herbivore did not diverge between plant origins, we still observed parallel evolutionary shifts in leaf secondary metabolite and protease inhibitor production, which may confer resistance to diverse herbivore species. Synthesis. Observed evolutionary convergence for multiple plant traits, between the natural and manipulative experiments, emphasizes the role of insect herbivores as key drivers of plant adaptation and geographic differentiation.