Seed Dispersal as a Maternally Influenced Character: Mechanistic Basis of Maternal Effects and Selection on Maternal Characters in an Annual Plant

Maternal influences on progeny characters affect phenotypic correlations between characters expressed in maternal and progeny generations and consequently influence evolutionary responses to selection. Net selection on maternally influenced characters depends on selection both on the progeny character and on the maternal characters that influence it. I used seed dispersal in Cakile edentula as a system in which to identify the mechanisms of environmentally mediated maternal effects and to determine how selection on maternal characters alters the adaptive value of dispersal. In C. edentula, maternal morphology responds to conspecific density experienced by the mother. Maternal morphology in turn affects offspring (seed) dispersal and density and thereby offspring morphology and fitness. I estimated the magnitude of density-mediated maternal effects on dispersal and identified their mechanism by characterizing the plasticity of maternal morphology to density. I also measured density-dependent selection on maternal characters that influence dispersal. Maternal plasticity to density was caused by both allometric and nonallometric variation in morphology, and this plasticity resulted in a negative correlation between maternal and progeny density. Such negative maternal effects are expected to retard responses to selection. Maternal morphology influenced maternal fitness, in part through the relationship of fitness to maternal plant size and in part through size-independent fitness effects. Maternal phenotypes that promote dispersal, and thereby increase progeny fitness, were associated with decreased maternal fitness. Selection on dispersal at the level of progeny favors increased dispersal; maternal influences on dispersal, however, not only cause a greatly reduced adaptive value of dispersal but lead to the prediction of a slower response to selection.     

地中海沿岸沙丘土壤种子库的异质性

应用自然萌发法和物理筛选法相结合的方法,调查了地中海沿岸沙丘三种微生境土壤总种子库和永久种子库特征,用功能群的方法分析了微生境之间的土壤总种子库和永久土壤种子库的组成和结构差异,也分析了主要物种土壤种子库的微生境分布格局,分析了种子大小和土壤种子库中的种子永久性关系.发现地中海沿岸沙丘土壤种子库具有明显的空间异质性,即使在相同的微生境内,土壤种子库的分布也不是均匀的,甚至具有很大的差异;微生境对总的土壤种子库和各功能群的土壤种子库的分布格局具有显著的影响,开阔地区域具有最大的种子密度,而灌丛下和路径具有较小的种子密度;在永久土壤种子库中,豆科类植物种子在休眠种子中占有最大的比例,约为76%,而一年生和多年生禾草未发现休眠种子,豆类、伞形科类、多年生阔草、菊科类、一年生阔叶草和十字花科类等种子在土壤中的永久性比例依次下降,分别为50%、46%、41%、6%、6%和1%,微生境影响各功能群种子在土壤中的永久性.微生境显著影响大部分主要物种的土壤种子库分布;种子大小与其在土壤中的永久性为正相关,即大种子具有较高的永久性,小种子具有较低的永久性.     

地中海沿岸沙丘土壤种子库的异质性

应用自然萌发法和物理筛选法相结合的方法,调查了地中海沿岸沙丘三种微生境土壤总种子库和永久种子库特征,用功能群的方法分析了微生境之间的土壤总种子库和永久土壤种子库的组成和结构差异,也分析了主要物种土壤种子库的微生境分布格局,分析了种子大小和土壤种子库中的种子永久性关系。发现地中海沿岸沙丘土壤种子库具有明显的空间异质性,即使在相同的微生境内,土壤种子库的分布也不是均匀的,甚至具有很大的差异;微生境对总的土壤种子库和各功能群的土壤种子库的分布格局具有显著的影响,开阔地区域具有最大的种子密度,而灌丛下和路径具有较小的种子密度;在永久土壤种子库中,豆科类植物种子在休眠种子中占有最大的比例,约为76％,而一年生和多年生禾草未发现休眠种子,豆类、伞形科类、多年生阔草、菊科类、一年生阔叶草和十字花科类等种子在土壤中的永久性比例依次下降,分别为50％、46％、41％、6％、6％和1％,微生境影响各功能群种子在土壤中的永久性。微生境显著影响大部分主要物种的土壤种子库分布;种子大小与其在土壤中的永久性为正相关,即大种子具有较高的永久性,小种子具有较低的永久性。     

Effects of Ca- and Fe-rich Seepage on P Availability and Plant Performance in Calcareous Dune Soils

Ca- and Fe-rich seepage in wet dune slacks often sustains oligotrophic, species rich vegetation as a result of reduced P availability. While this effect has been attributed to pH buffering, we tested whether Ca- and Fe-rich seepage also immobilised P in calcareous soils with a strong pH buffer. Two oligotrophic species (Carex flacca and Schoenus nigricans) and two eutrophic species (Calamagrostis epigejos and Molinia caerulea) were planted in experimental sods. After 4 months supply with water of seepage or infiltration quality, with or without the addition of P, soil P fractions and a number of plant physiological responses were measured. A field validation was performed in a flow-through lake in calcareous dunes where the seepage flow had been restored recently. The readily available water soluble P fraction (Pw) was reduced by more than 80% by seepage, both in the greenhouse experiment and in the field, but the P Olsen-inorganic fraction was unaffected. All four test species had elevated N: P ratios in aboveground tissues when treated with seepage, indicating that seepage water had indeed reduced P availability to plants. Formation of dauciform roots by Carex flacca was diminished by P addition to less than 25% of treatments without P addition, indicating sensitivity to P availability, while seepage on average halved production of these root structures. Dauciform root formation by Schoenus nigricans was unaffected by the P addition and the hydrological treatment. Biomass of the test species in the experiment as well as vegetation biomass and relative abundance of oligotrophic species in the field were unrelated to seepage patterns, suggesting that compensatory mechanisms enabled the plants to sustain biomass production within the time frame of this experiment. In conclusion, Ca- and Fe-rich seepage can lower P availability in soils with a strong pH buffer. In the long term, this may create favourable conditions for species that have low P requirements or efficient P uptake. In the short term, however, existing vegetation seems to be resilient to changes in P supply.     

Effect of an Invasive Plant and Moonlight on Rodent Foraging Behavior in a Coastal Dune Ecosystem

Understanding how invasive plants may alter predator avoidance behaviors is important for granivorous rodents because their foraging can trigger ripple effects in trophic webs. Previous research has shown that European beach grass Ammophila arenaria, an invasive species in coastal California, affects the predation of other seeds by the rodents Microtus californicus, Peromyscus maniculatus, and Reithrodontomys megalotis. This may be due to lower perceived predation risk by rodents foraging in close proximity to the cover provided by Ammophila, but this mechanism has not yet been tested. We examined the perceived predation risk of rodents by measuring the ‘giving up density’ of food left behind in experimental patches of food in areas with and without abundant cover from Ammophila and under varying amount of moonlight. We found strong evidence that giving up density was lower in the thick uniform vegetation on Ammophila-dominated habitat than it was in the more sparsely and diversely vegetated restored habitat. There was also evidence that moonlight affected giving up density and that it mediated the effects of habitat, although with our design we were unable to distinguish the effects of lunar illumination and moon phase. Our findings illustrate that foraging rodents, well known to be risk-averse during moonlit nights, are also affected by the presence of an invasive plant. This result has implications for granivory and perhaps plant demography in invaded and restored coastal habitats. Future research in this system should work to unravel the complex trophic links formed by a non-native invasive plant (i.e., Ammophila) providing cover favored by native rodents, which likely forage on and potentially limit the recruitment of native and non-native plants, some of which have ecosystem consequences of their own.     

Sexual Conflict and Sexually Antagonistic Coevolution in an Annual Plant

Background

Sexual conflict theory predicts sexually antagonistic coevolution of reproductive traits driven by conflicting evolutionary interests of two reproducing individuals. Most studies of the evolutionary consequences of sexual conflicts have, however, to date collectively investigated only a few species. In this study we used the annual herb Collinsia heterophylla to experimentally test the existence and evolutionary consequences of a potential sexual conflict over onset of stigma receptivity.

Methodology/Principal Findings

We conducted crosses within and between four greenhouse-grown populations originating from two regions. Our experimental setup allowed us to investigate male-female interactions at three levels of geographic distances between interacting individuals. Both recipient and pollen donor identity affected onset of stigma receptivity within populations, confirming previous results that some pollen donors can induce stigma receptivity. We also found that donors were generally better at inducing stigma receptivity following pollen deposition on stigmas of recipients from another population than their own, especially within a region. On the other hand, we found that donors did worse at inducing stigma receptivity in crosses between regions. Interestingly, recipient costs in terms of lowered seed number after early fertilisation followed the same pattern: the cost was apparent only if the pollen donor belonged to the same region as the recipient.

Conclusion/Significance

Our results indicate that recipients are released from the cost of interacting with local pollen donors when crossed with donors from a more distant location, a pattern consistent with a history of sexually antagonistic coevolution within populations. Accordingly, sexual conflicts may have important evolutionary consequences also in plants.     

Vegetative Plant Growth Analysis in Controlled Environments

Current techniques for analysing growth are compared using datafrom young plants grown in artificially-lit growth cabinets.A statistical method of fitting curves to log dry weight andlog leaf areas led to values which often diverged from biologicalexpectation. It was more satisfactory to make the calculationsassuming that a quadratic relation always applied. It appears that the statistical methods cannot be used unmodifiedfor experiments involving comparisons between artificially-litcabinets. Cabinet environments are seldom replicated and thereforethe consequences of isolated anomalies in either the environmentor in a particular harvest are not allowed for and are reproducedin the final curves. In addition the statistical method assumesthat all the growth curves are entirely independent, whereasthere is a tendency for the opposite to be true.     

Dissecting Genetic Architecture Underlying Seed Traits in Multiple Environments

The seeds of flowering plants develop from double fertilization and play a vital role in reproduction and supplying human and animal food. The genetic variation of seed traits is influenced by multiple genetic systems, e.g., maternal, embryo, and/or endosperm genomes. Understanding the genetic architecture of seed traits is a major challenge because of this complex mechanism of multiple genetic systems, especially the epistasis within or between different genomes and their interactions with the environment. In this study, a statistical model was proposed for mapping QTL with epistasis and QTL-by-environment (QE) interactions underlying endosperm and embryo traits. Our model integrates the maternal and the offspring genomes into one mapping framework and can accurately analyze maternal additive and dominant effects, endosperm/embryo additive and dominant effects, and epistatic effects of two loci in the same or two different genomes, as well as interaction effects of each genetic component of QTL with environment. Intensive simulations under different sampling strategies, heritabilities, and model parameters were performed to investigate the statistical properties of the model. A set of real cottonseed data was analyzed to demonstrate our methods. A software package, QTLNetwork-Seed-1.0.exe, was developed for QTL analysis of seed traits.     

Within and Between Plant Variation in Seed Number, Seed Mass and Germinability of Primula elatior: Effect of Population Size

Abstract: In this study, natural variation of seed mass and seed number between and within individual plants of P. elatior, a common forest herb on rich soils in Flanders, was investigated for both small (< 50 flowering individuals) and large (> 1000 flowering individuals) populations. The relationship between seed number and seed mass at both the between and within population level was also quantified. We also investigated how population size affected germinability of seeds through the effects of seed mass. Seed number varied by a factor of twenty, whereas seed mass spanned, on average, a 3.5 range. In both cases variation was highest among populations, indicating that population size has important effects on seed number and seed mass. Next, seed number-seed mass tradeoffs were significantly influenced by population size, with small populations showing strong negative relationships whereas in large populations seed mass was only marginally influenced by seed number. As to germination, larger seeds showed larger germination percentages only for the smallest population. In all other populations, seed mass had little effect on germination.     

Proteinase Inhibitors in Plant Seed

Three different types of proteinase inhibitors, I, II and III, were fractionated from Japanese radish seed by repeated column chromatographies on SE- and CM-cellulose. The finally purified preparation of inhibitor III was found to be homogeneous by both chromatographic and electrophoretic analyses. All three of them strongly and stoichiometrically inhibited trypsin whereas they showed weak inhibition on other proteinases, such as chymotrypsin, Nagarse and Pronase. From nitrogen content and ultraviolet absorption spectra, each of the inhibitors I and III was confirmed to be a protein. The molecular weights of inhibitors I and III were calculated to be 8000 and 12,000, respectively. These inhibitors were stable at temperatures above 90°C in an acidic pH.     

向日葵种群中植株个体大小对其氮素利用策略的影响

我们利用Berendse和Aerts提出的氮素利用效率(NUE)概念及原理研究了高密度一年生草本植物向日葵(Helianthus annuus L.)种群中植株个体大小对其氮素吸收利用的影响,并对种内竞争进行了分析。结果表明,植株对氮素的吸收与其个体大小不成线性关系,说明种群内不同植株个体对土壤氮素的竞争属于非对称竞争。植株的氮素损失随着个体大小的增加而增加。个体较大的植株具有较高的氮素输入率和较低的氮素输出率,因而具有较高的氮素净增加值。植株的氮素生产力(NP)和氮素平均滞留时间(MRT)均与植株个体大小呈正相关。较大的植物个体具有较高的NP和较长的MRT,由于NUE为NP和MRT二者的乘积,因而较大个体植株的NUE高于个体较小的植株。同种植物的不同个体的NP和MRT之间不存在协衡关系。氮素回收效率(NRE)与植株个体大小密切相关。在个体水平上,较大的植株个体具有较高的NUE与其较高的NRE有关。种群内植株个体对土壤氮素的非对称竞争主要由于植株对氮素的吸收和利用效率不同所致。因此,Berendse和Aerts提出的氮素利用效率概念不仅适用于研究种间的养分利用策略,对于种内不同植株的养分策略研究也同样适用。     

向日葵种群中植株个体大小对其氮素利用策略的影响

我们利用Berendse和Aerts提出的氮素利用效率(NUE)概念及原理研究了高密度一年生草本植物向日葵(Helianthus annuus L.)种群中植株个体大小对其氮素吸收利用的影响,并对种内竞争进行了分析.结果表明,植株对氮素的吸收与其个体大小不成线性关系,说明种群内不同植株个体对土壤氮素的竞争属于非对称竞争.植株的氮素损失随着个体大小的增加而增加.个体较大的植株具有较高的氮素输入率和较低的氮素输出率,因而具有较高的氮素净增加值.植株的氮素生产力(NP)和氮素平均滞留时间(MRT)均与植株个体大小呈正相关.较大的植物个体具有较高的NP和较长的MRT,由于NUE为NP和MRT二者的乘积,因而较大个体植株的NUE高于个体较小的植株.同种植物的不同个体的NP和MRT之间不存在协衡关系.氮素回收效率(NRE)与植株个体大小密切相关.在个体水平上,较大的植株个体具有较高的NUE与其较高的NRE有关.种群内植株个体对土壤氮素的非对称竞争主要由于植株对氮素的吸收和利用效率不同所致.因此,Berendse和Aerts提出的氮素利用效率概念不仅适用于研究种间的养分利用策略,对于种内不同植株的养分策略研究也同样适用.     

Effects of Biological Soil Crusts on Seed Bank, Germination and Establishment of Two Annual Plant Species in the Tengger Desert (N China)

The presence of biological soil crusts can affect the germination and survival of vascular plants, but the reasons are not well investigated. We have conducted a field investigation and greenhouse experiments to test the effect of crusts on two desert annual plants, which occur on the stabilized dunes of the Tengger Desert in N China. The results showed that biological soil crusts negatively influenced the seed bank of Eragrostis poaeoides and Bassia dasyphylla. The important effect of biological soil crusts on seed germination and establishment were performed indirectly through reducing the amount of germinating seeds. Field investigation and experimental results with regard to the seed bank indicated that higher seedling density was found in disturbed crust soil and bare soil surface than in intact crust soils. Greenhouse experiments showed that the effects of biological soil crusts on germination and establishment of the two plants are not obvious in moist condition, while disturbed crusts are more favorable to seed germination in dry treatment. Significant differences in biomass were found between disturbed crust soil and bare soil. Survival and growth of the two annual plants were enhanced in both algal and moss crusts during the season of rainfall or in moist environment, but crusts did not affect seedling survival in the dry period. The small seeded E. poaeoides has higher germination than larger-seeded B. dasyphylla in crust soils, but B. dasyphylla has a relatively higher survival rate than E. poaeoides in crust soils.     

Rapid Development of Adaptive,Climate-Driven Clinal Variation in Seed Mass in the Invasive Annual Forb Echium plantagineum L.

We examined adaptive clinal variation in seed mass among populations of an invasive annual species, Echium plantagineum, in response to climatic selection. We collected seeds from 34 field populations from a 1,000 km long temperature and rainfall gradient across the species'' introduced range in south-eastern Australia. Seeds were germinated, grown to reproductive age under common glasshouse conditions, and progeny seeds were harvested and weighed. Analyses showed that seed mass was significantly related to climatic factors, with populations sourced from hotter, more arid sites producing heavier seeds than populations from cooler and wetter sites. Seed mass was not related to edaphic factors. We also found that seed mass was significantly related to both longitude and latitude with each degree of longitude west and latitude north increasing seed mass by around 2.5% and 4% on average. There was little evidence that within-population or between-population variation in seed mass varied in a systematic manner across the study region. Our findings provide compelling evidence for development of a strong cline in seed mass across the geographic range of a widespread and highly successful invasive annual forb. Since large seed mass is known to provide reproductive assurance for plants in arid environments, our results support the hypothesis that the fitness and range potential of invasive species can increase as a result of genetic divergence of populations along broad climatic gradients. In E. plantagineum population-level differentiation has occurred in 150 years or less, indicating that the adaptation process can be rapid.     

植物生长调节剂对降香黄檀种子萌发的影响

用6-BA、IBA、GA 3等3种植物生长调节剂对降香黄檀种子进行萌发处理,测定降香黄檀种子中可溶性糖、淀粉、蛋白质和脂肪含量的变化。结果表明,降香黄檀种子在不同的萌发处理过程中,可溶性糖含量均呈下降趋势,萌发结束时淀粉含量由第3 d的0.6%下降至0.2%以下,其中6-BA处理后种子萌发前期（3～6 d）淀粉含量变化不大,后期则有一个显著的下降趋势;3种植物生长调节剂对降香黄檀种子蛋白质、脂肪含量变化影响不明显。     

Waterlogging Stress and Ethylene Production in the Dune Slack Plant, Scirpus americanus

The sedge, Scirpus americanus Pers., grows in dune slacks andother freshwater and brackish water wetland communities. Whenwaterlogged in a greenhouse, the concentration of ethylene increased4-fold in stems of S. americanus plants. This increase was associatedwith a decrease in plant height and an increase in aerenchymaas exhibited under waterlogged conditions. Endogenous ethyleneproduction in S. americanus was compared to that in anotherdune slack species, Panicum amarulum, and also to Spartina aherniflorafrom a salt marsh. These species did not respond by increasingendogenous ethylene upon waterlogging. In the field, a 16 cmrainfall significantly increased the endogenous ethylene productionin S. americanus. As the water table subsided the concentrationof accumulated ethylene in stem tissue decreased. Exposure ofS. americanus to exogenous ethylene inhibited stem extensionand increased aerenchyma formation, thus linking ethylene tothe morphological characteristics of waterlogged plants of thisspecies. These experiments support the hypothesis that ethylenemodulates S. americanus morphology in natural waterlogged environmentsand may be of importance in adapting this species to life inthe wetland environment. Key words: Dune slack, waterlogging, ethylene     

Legacies of Prehistoric Agricultural Practices Within Plant and Soil Properties Across an Arid Ecosystem

Closely integrated research between archaeologists and ecologists provides a long-term view of human land use that is rare in the ecological literature, allowing for investigation of activities that lead to enduring environmental outcomes. This extended temporal perspective is particularly important in aridlands where succession occurs slowly and ecosystem processes are mediated by abiotic, geomorphic factors. Numerous studies show that impacts from ancient human actions can persist, but few have explored the types of practices or mechanisms that lead to either transient or long-term environmental change. We compared plant and soil properties and processes from a range of landscape patch types in the Sonoran Desert of the US Southwest that supported different, well-documented prehistoric farming practices from AD 750–1300. Our results show that the types of ancient human activities that leave long-term ecological legacies in aridlands are those that fundamentally alter “slow variables” such as soil properties that regulate the timing and supply of water. Prehistoric Hohokam floodwater-irrigation practices, but not dryland farming techniques, substantially altered soil texture, which was strongly associated with desert plant community and functional composition. However, prehistoric agriculture did not consistently alter long-term nutrient availability and thus had no impact on “fast variables” such as production of seasonal annual plants that are restricted to periods of ample rainfall. In this arid ecosystem, the inverse texture model explained patterns in plant functional composition at large scales, but is less predictive of production of short-lived desert annuals that experience a more mesic precipitation regime.