Impacts of ecosystem engineers on community attributes: effects of cushion plants at different elevations of the Chilean Andes

Ecosystem engineers are organisms able to modulate environmental forces and, hence, may change the habitat conditions for other species. In so doing, ecosystem engineers may affect both species richness and evenness of communities and, in consequence, change species diversity. If these changes in community attributes are related to the magnitude of the habitat changes induced by the engineers, it seems likely that engineer species will have greater effects on diversity in sites where they cause larger habitat changes. We addressed this issue by evaluating the effects of three alpine cushion plants on species richness, evenness, and diversity of high-Andean plant communities. Given that the difference in microclimatic conditions between cushions and the external environment increases with elevation, we proposed that these organisms should have greater effects on community attributes at higher than at lower elevation sites. Results showed that the three cushion species had positive effects on species richness, diversity, and evenness of plant communities. It was also observed that the magnitude of these effects changed with elevation: positive effects on species richness and diversity increased towards upper sites for the three cushions species, whereas positive effects on evenness increased with elevation for one cushion species but decreased with elevation for other two cushion species. These results suggest that the presence of cushions is important to maintain plant diversity in high-Andean communities, but this positive effect on diversity seems to increase as the difference in environmental conditions between cushions and the external environment increases with elevation.     

Rapid response to intraclonal selection in the pea aphid (Acyrthosiphon pisum)

Summary Pea aphids show intraclonal variability in antipredator behaviour. Among the offspring of a single parthenogenetically reproducing female, some individuals drop from the plant in response to alarm pheromone while others remain on the plant. We demonstrate that this intraclonal behavioural variability can be altered by selection. The proportion of aphids dropping in response to alarm pheromone was significantly greater in lines in which this behaviour was selected than in clonally identical lines in which the opposite phenotype was favoured. This change occurred within one generation and could not be attributed to grand-maternal effects, nor to environmental effects. These results demonstrate the ability of clonal aphids to adapt to changes in the environment within a single generation.     

Parental environmental effects on life history traits in Arabidopsis thaliana (Brassicaceae)

Environmentally induced maternal effects on offspring phenotype are well known in plants. When genotypes or maternal lineages are replicated and raised in different environmental conditions, the phenotype of their offspring often depends on the environment in which the parents developed. However, the degree to which such maternal effects are maintained over subsequent generations has not been documented in many taxa. Here we report the results of a study designed to assess the effects of parental environment on vegetative and reproductive traits, using glasshouse-raised maternal lines sampled from natural populations of Arabidopsis thaliana . Replicates of five highly selfed lines from each of four wild populations were cultivated in two abiotic environments in the glasshouse, and the quality and performance of seeds derived from these two environments were examined over two generations. We found that offspring phenotype was strongly influenced by parental environment, but because the parental environments differed with respect to the time of seed harvest, it was not possible to distinguish clearly between parental environmental effects and the possible (but unlikely) effects of seed age on offspring phenotype. We observed a rapid decline in the expression of ancestral environmental effects, and no main environmental effects on progeny phenotype persisted in the second generation. The mechanism of transmission of environmental effects did not appear to be associated with the quantity or quality of reserves in the seeds, suggesting that environmental effects may be transmitted across subsequent generations via some mechanism that generates environment-specific gene expression.     

Variation among populations of Diodia teres (Rubiaceae) in environmental maternal effects

Previous studies have quantified variation in environmental maternal effects (EME) within populations, but these effects could differ among populations as well. In this study we grew clonal replicates of individuals from three populations of the annual plant Diodia teres in their native and non-native environments. Our goal was to estimate the effects of maternal environment and maternal population on seed and seedling traits. Seeds that were produced in this field study were then planted in two soil types to quantify effects of the offspring environment on seedling traits. There was substantial variation among populations for seed weight. We found population variation for EME, and maternal environment by offspring environment interactions. We conclude that variation among populations in EME may be an unrecognized component of local adaptation, and that attempts to control maternal effects by statistically accounting for variation in seed weight may be ineffective.     

克隆和有性亲体效应及其调控机制

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。     

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.

     

Interactive effects of builders and exploiters on environmental quality and the outcome of competition between the two

The implications of spatial and temporal structure for the maintenance of mutualism, altruism, and niche construction or ecosystem engineering have been explored by many theoretical models. Part of what these models have shown is that organisms that give up some amount of potential short-term gain in order to improve the quality of their environment can, in a variety of scenarios, persist in the face of more exploitative competitors if structure in environmental quality allows the former to preferentially benefit from their investments. The models presented here consider the additional implications of interactions between competitors in their effects on their environment (recently documented in multiple systems). Relative to when competitor types were additive, synergistic effects promoted coexistence and antagonistic effects promoted founder effects (but favored the less exploitative type when both had equal initial frequencies). Spatial and temporal patterns of patch quality and occupancy also differed markedly between scenarios, even where all three scenarios generated the same qualitative outcome. These models show that understanding both the scale over which organisms affect their environment and the degree to which organisms interact in such effects are important for interpreting patterns in environmental quality, predicting the effects of organism-environment feedback on competition, and explaining the persistence of mutualistic traits.     

克隆植物对异质生境的适应对策研究进展

生境异质性是自然生态系统的基本特征,植物生长的必需资源和环境胁迫因子均存在着复杂的时间和空间异质性。克隆植物是指在自然条件下具有克隆特性的植物,即可通过与母株相连的芽、根茎、分蘖或枝条等繁殖体产生无性繁殖的植物,这些繁殖体一旦定居便可成为潜在的独立个体。克隆植物具有独特的生境适应策略(如形态可塑性、克隆整合、克隆分工、觅食行为、风险分摊等),面对异质性的生境条件,它可以通过调整自身的生理和形态结构来适应异质生境。目前,对于克隆植物在异质生境适应行为的研究已有很多报道,然而系统性的归纳和总结尚有欠缺。综述了克隆植物在不同资源异质生境(光照、养分、水分)和不同胁迫生境(盐碱胁迫、风沙胁迫、重金属胁迫)下独特的适应对策。最后,针对克隆植物对异质生境的适应对策,进行了总结并对未来的重点研究方向提出建议：(1)时间异质性尺度上的考量;(2)异质性生境中生物因子的调控作用;(3)克隆植物入侵机制;(4)克隆植物在生态修复中的应用潜力。     

On the ecological and evolutionary significance of storage in clonal plants

Environmental heterogeneity has received wide attention in clonal plant research over the last decade. Most studies have focussed on the effects of spatial variation in environmental conditions on the performance of ramets and genets, while the effects of temporal heterogeneity have only occasionally been studied. As a consequence, our current knowledge about functional responses of clonal plants to habitat patchiness is biased towards spatial aspects of environmental heterogeneity. Nevertheless, temporal changes in biotic and abiotic conditions do occur in most natural habitats, and they are very likely to affect plant growth and performance, and to create positive selection pressures on traits that can buffer plants against unfavorable consequences of this variability. Storage of resources is a widespread phenomenon in clonal plant species. Typical clonal structures such as stolons, rhizomes and hibernacles serve as storage organs. However, the ecologic significance of storage in clonal plant structures remains partly unclear. We suggest that the lack of understanding with respect to resource storage in clonal plants be related to our poor knowledge of ecologic implications of temporal habitat heterogeneity in natural environments. Resource storage can be understood as a safety measure against temporal changes in the growing conditions of plants. This paper summarizes existing information about the ecologic relevance of storage in clonal plants and it tries to develop a framework for further investigation of resource storage as a strategy to enhance the performance of clonal plants in temporally variable environments.     

Mother's timing and duration of corticosterone exposure modulate offspring size and natal dispersal in the common lizard (Lacerta vivipara)

Although multiple condition dependence in dispersal is common, the proximate mechanisms that integrate information from multiple sources remain largely unknown. In the common lizard (Lacerta vivipara), earlier studies have shown that maternal plasma corticosterone level interacts with maternal phenotype to affect offspring phenotype and dispersal strategy, and may reflect the mother's external and/or internal environment. However, the mechanism by which these two types of environmental information are integrated has not been identified. We explored the possibility that the timing and duration of the corticosterone signal are the key factors by which the message is modulated. We found that the timing of corticosterone exposure affects the juvenile phenotype: an exposure to corticosterone early in development has negative effects on juvenile size, weight, and body condition, that can nevertheless be restored in the case of a prolonged exposure. The duration of corticosterone exposure affects the dispersal strategy, although the precise effect depends on the sex ratio of the clutch. That is, in female-biased clutches, a prolonged exposure during gestation promotes philopatry of juveniles, while a short exposure enhances their dispersal, a result that is consistent with kin competition theory. Therefore, our results demonstrate that while corticosterone titer may signal a mother's external and/or internal environment to her developing young, differences in the timing and duration of this endocrine signal produce offspring with specialized phenotypes that exhibit different dispersal strategies.     

Clonal Transgenerational Effects Transmit for Multiple Generations in a Floating Plant

Environmental conditions of a parent plant can influence the performance of their clonal offspring, and such clonal transgenerational effects may help offspring adapt to different environments. However, it is still unclear how many vegetative generations clonal transgenerational effects can transmit for and whether it depends on the environmental conditions of the offspring. We grew the ancestor ramets of the floating clonal plant Spirodela polyrhiza under a high and a low nutrient level and obtained the so-called 1^st-generation offspring ramets of two types (from these two environments). Then we grew the 1^st-generation offspring ramets of each type under the high and the low nutrient level and obtained the so-called 2^nd-generation offspring ramets of four types. We repeated this procedure for another five times and analyzed clonal transgenerational effects on growth, morphology and biomass allocation of the 1^st- to the 6^th-generation offspring ramets. We found positive, negative or neutral (no) transgenerational effects of the ancestor nutrient condition on the offspring of S. polyrhiza, depending on the number of vegetative generations, the nutrient condition of the offspring environment and the traits considered. We observed significant clonal transgenerational effects on the 6^th-generation offspring; such effects occurred for all three types of traits (growth, morphology and allocation), but varied depending on the nutrient condition of the offspring environment and the traits considered. Our results suggest that clonal transgenerational effects can transmit for multiple vegetative generations and such impacts can vary depending on the environmental conditions of offspring.     

Transgenerational acclimatization in an herbivore–host plant relationship

Twenty years ago, scientists began to recognize that parental effects are one of the most important influences on progeny phenotype. Consequently, it was postulated that herbivorous insects could produce progeny that are acclimatized to the host plant experienced by the parents to improve progeny fitness, because host plants vary greatly in quality and quantity, and can thus provide important cues about the resources encountered by the next generation. However, despite the possible profound implications for our understanding of host-use evolution of herbivores, host-race formation and sympatric speciation, intense research has been unable to verify transgenerational acclimatization in herbivore–host plant relationships. We reared Coenonympha pamphilus larvae in the parental generation (P) on high- and low-quality host plants, and reared the offspring (F₁) of both treatments again on high- and low-quality plants. We tested not only for maternal effects, as most previous studies, but also for paternal effects. Our results show that parents experiencing predictive cues on their host plant can indeed adjust progeny''s phenotype to anticipated host plant quality. Maternal effects affected female and male offspring, whereas paternal effects affected only male progeny. We here verify, for the first time to our knowledge, the long postulated transgenerational acclimatization in an herbivore–host plant interaction.     

Infection by the systemic fungus Epichloë glyceriae alters clonal growth of its grass host,Glyceria striata

Parasites and pathogens are hypothesized to change host growth, reproduction and/or behaviour to increase their own transmission. However, studies which clearly demonstrate that parasites or pathogens are directly responsible for changes in hosts are lacking. We previously found that infection by the systemic fungus Epichloë glyceriae was associated with greater clonal growth by its host, Glyceria striata. Whether greater clonal growth resulted directly from pathogen infection or indirectly from increased likelihood of infection for host genotypes with greater clonal growth could not be determined because only naturally infected and uninfected plants were used. In this study, we decoupled infection and host genotype to evaluate the role of pathogen infection on host development and clonal growth. We found that total biomass production did not differ for clones of the same genotype, but infected clones allocated more biomass to clonal growth. Disinfected clones had more tillers and a greater proportion of their biomass in the mother ramet. Infected clones produced fewer tillers but significantly more and longer stolons than disinfected clones. These results support the hypothesis that pathogen infection directly alters host development. Parasite alteration of clonal growth patterns might be advantageous to the persistence and spread of host plants in some ecological conditions.     

The role of transgenerational effects in adaptation of clonal offspring of white clover (<Emphasis Type="Italic">Trifolium repens</Emphasis>) to drought and herbivory

Environmentally induced transgenerational effects can increase success of offspring and thereby be adaptive if offspring experience conditions similar to the parental environment. The ecological and evolutionary significance of these effects in plants have been considered overwhelmingly in the context of sexual generations. We investigated whether drought stress and jasmonic acid, a key hormone involved in induction of plant defenses against herbivores, applied in the parental generation, trigger transgenerational effects in clonal offspring of Trifolium repens and whether these effects are adaptive. We found that drought stress experienced by parents significantly affected phenotypes of offspring ramets. Offspring ramets were bigger if they were produced in the parental water regime (control/drought). Repeated application of jasmonic acid to parents increased the subsequent growth of offspring ramets produced by stolons after they were disconnected from the parental clone. However, these offspring ramets experienced similar herbivory by the generalist Spodoptera littoralis caterpillar as did control offspring ramets, indicating that this jasmonic acid application in the parental generation did not result in a transgenerational effect comprising increased herbivory resistance. We conclude that, overall, environmental interaction in the parental generation can trigger transgenerational effects in clonal plants and some of these effects can be adaptive. Moreover, transgenerational effects in clonal plants that significantly influence their growth and behavior can ultimately affect the evolutionary trajectories of clonal populations.     

Separating parental environment from seed size effects on next generation growth and development in Arabidopsis

Plant growth and development is profoundly influenced by environmental conditions that laboratory experimentation typically attempts to control. However, growth conditions are not uniform between or even within laboratories and the extent to which these differences influence plant growth and development is unknown. Experiments with wild-type Arabidopsis thaliana were designed to quantify the influences of parental environment and seed size on growth and development in the next generation. A single lot of seed was planted in six environmental chambers and grown to maturity. The seed produced was mechanically sieved into small and large size classes then grown in a common environment and subjected to a set of assays spanning the life cycle. Analysis of variance demonstrated that seed size effects were particularly significant early in development, affecting primary root growth and gravitropism, but also flowering time. Parental environment affected progeny germination time, flowering and weight of seed the progeny produced. In some cases, the parental environment affected the magnitude of (interacted with) the observed seed size effects. These data indicate that life history circumstances of the parental generation can affect growth and development throughout the life cycle of the next generation to an extent that should be considered when performing genetic studies.     

Different gardens, different results: native and introduced populations exhibit contrasting phenotypes across common gardens

Invasive plants may respond through adaptive evolution and/or phenotypic plasticity to new environmental conditions where they are introduced. Although many studies have focused on evolution of invaders particularly in the context of testing the evolution of increased competitive ability (EICA) hypothesis, few consistent patterns have emerged. Many tests of the EICA hypothesis have been performed in only one environment; such assessments may be misleading if plants that perform one way at a particular site respond differently across sites. Single common garden tests ignore the potential for important contributions of both genetic and environmental factors to affect plant phenotype. Using a widespread invader in North America, Cynoglossum officinale, we established reciprocal common gardens in the native range (Europe) and introduced range (North America) to assess genetically based differences in size, fecundity, flowering phenology and threshold flowering size between native and introduced genotypes as well as the magnitude of plasticity in these traits. In addition, we grew plants at three nutrient levels in a pot experiment in one garden to test for plasticity across a different set of conditions. We did not find significant genetically based differences between native and introduced populations in the traits we measured; in our experiments, introduced populations of C. officinale were larger and more fecund, but only in common garden experiments in the native range. We found substantial population-level plasticity for size, fecundity and date of first flowering, with plants performing better in a garden in Germany than in Montana. Differentiation of native populations in the magnitude of plasticity was much stronger than that of introduced populations, suggesting an important role for founder effects. We did not detect evidence of an evolutionary change in threshold flowering size. Our study demonstrates that detecting genetically based differences in traits may require measuring plant responses to more than one environment.     

Environmental and spatial controls of biotic assemblages in a discrete semi‐terrestrial habitat: comparison of organisms with different dispersal abilities sampled in the same plots

Aim The development of metacommunity theory inspired a series of studies exploring the importance of environmental and spatial effects on the composition of biotic assemblages. However, the comparison of different groups of organisms has been hampered by differences in sampling design, spatial scales or the environmental variables involved. Our aim was to test how dispersal ability affects metacommunity structure and associated species distributions by sampling different species groups in the same plots to avoid these problems. Location Western Carpathian Mountains (Europe). Methods In 191 fens we sampled the composition of diatom, bryophyte, vascular plant and mollusc assemblages, water chemistry, and macroclimatic data. We then generated spatial variables covering all relevant spatial scales using analysis of principal coordinates of neighbour matrices (PCNM). We applied the adjusted variation partitioning algorithm to quantify the effects of environment and space. Results Pure effects of water chemistry and space were highly significant for all groups of organisms. Spatial effects were stronger for groups with larger propagules (vascular plants, molluscs) than for those with smaller propagules (diatoms, bryophytes). Assemblages of macroscopic bryophytes were structured slightly less by geography and much more by environment than were those of microscopic diatoms. Vascular plant and mollusc assemblages turned out to be more spatially structured (as compared to diatom and bryophyte assemblages), with small differences between the two groups. Coarse‐scale spatial effects dominated in the bryophyte metacommunity, while in the other groups, including diatoms, finer‐scale effects were also important. Main conclusions Given that our analyses are based on a standardized sampling and analytical framework, our findings provide strong support for the hypothesis that both environmental and spatial variables structure metacommunities of organisms with very different dispersal abilities, including microscopic diatoms. In addition, we show for the first time that the strengths of these effects and their scale dependence may be predicted using important trait differences between organisms, for example differences in propagule size.     

Fitness and evolution in clonal plants: the impact of clonal growth

Seeds have often been emphasized in estimates of plant fitness because they are the units that carry genes to the next generation, disperse, and found new populations. We contend that clonal growth also needs to be considered when estimating fitness in clonal plants, regardless of whether fitness is measured from a genet or ramet perspective. Clonal growth affects genet fitness through both genet persistence and seed production. It affects ramet fitness through new ramet production, because both seeds and clonal propagants are considered offspring. The differential production of clonal propagants will contribute to fitness differences among individuals which may result in population-level changes in allele frequencies (i.e. microevolution). We describe a form of selection unique to clonal organisms, genotypic selection, that can result in evolution. Genotypic selection occurs when genotypically based traits are associated with differences in the rate of ramet production. It can lead to evolutionary change in quantitative trait means both directly and indirectly. It leads directly to change in the ramet population by increasing the proportion of ramets with more advantageous trait values. From the genet perspective, it leads indirectly to evolution within and among populations whenever significant portions of the genetic effect on a trait are inherited through seed. We argue that under most conditions, clonal growth will play a major role in the microevolution of clonal plants.     

Clonal mobility and its implications for spatio‐temporal patterns of plant communities: what do we need to know next?

Patterns of clonal growth and their controls on the level of individuals have been studied thoroughly, but little is known about the actual clonal mobility of plant individuals in vegetation and about its role in generating vegetation patterns and influencing species coexistence. Current evidence shows that communities are composed of spatially nonmobile ‘matrix‐forming species’ and mobile ‘inter‐matrix’ species, while local between‐species variation in clonal mobility has been shown to be positively correlated to small‐scale richness. We identify two major gaps in the knowledge. (1) Clonal mobility has a strong species‐specific component, but the existing information is mainly qualitative and describes the potential mobility of species the best. Also, species may respond by their clonal growth in a plastic way to some environmental stimuli, such as neighbors or abiotic environment, but this data comes almost exclusively from artificial conditions. We know very little of the actual spatial mobility of clonal plant individuals in the field and of the factors that determine it. (2) Theoretical research indicates that localized dispersal plays prime role in determination of community structure. While clonal mobility shares many important features with the seed dispersal, it also shows important differences to it, such as in dispersal kernel (non‐monotonic in clonal dispersal), role of microsite limitation, and role of plasticity. We have little information how systematic are these differences, and whether these differences in dispersal can play any role in shaping community dynamics. We conclude that clonal mobility has an important role in structuring plant communities in a small scale and propose further studies to address specific mechanisms, as well as community context of evolution of clonality.