Background and Aims
Genome duplication is a central process in plant evolution and contributes to patterns of variation in genome size within and among lineages. Studies that combine cytogeography with genome size measurements contribute to our basic knowledge of cytotype distributions and their associations with variation in genome size.
Ploidy and genome size were assessed with direct chromosome counts and flow cytometry for 78 populations within the Claytonia perfoliata complex, comprised of three diploid taxa with numerous polyploids that range to the decaploid level. The relationship between genome size and temperature and precipitation was investigated within and across cytotypes to test for associations between environmental factors and nuclear DNA content.
A euploid series (n = 6) of diploids to octoploids was documented through chromosome counts, and decaploids were suggested by flow cytometry. Increased variation in genome size among populations was found at higher ploidy levels, potentially associated with differential contributions of diploid parental genomes, variation in rates of genomic loss or gain, or undetected hybridization. Several accessions were detected with atypical genome sizes, including a diploid population of C. parviflora ssp. grandiflora with an 18 % smaller genome than typical, and hexaploids of C. perfoliata and C. parviflora with genomes 30 % larger than typical. There was a slight but significant association of larger genome sizes with colder winter temperature across the C. perfoliata complex as a whole, and a strong association between lower winter temperatures and large genome size for tetraploid C. parviflora.
The C. perfoliata complex is characterized by polyploids ranging from tetraploid to decaploid, with large magnitude variation in genome size at higher ploidy levels, associated in part with environmental variation in temperature.
Claytonia perfoliata; Portulacaceae; flow cytometry; C-value; cytogeography; genome duplication; DNA content
Background and Aims
Gene determination of flowering is the result of complex interactions involving both promoters and inhibitors. In this study, the expression of flowering-related genes at the meristem level in alternate-bearing citrus trees is analysed, together with the interplay between buds and leaves in the determination of flowering.
First defruiting experiments were performed to manipulate blossoming intensity in ‘Moncada’ mandarin, Citrus clementina. Further defoliation was performed to elucidate the role leaves play in the flowering process. In both cases, the activity of flowering-related genes was investigated at the flower induction (November) and differentiation (February) stages.
Study of the expression pattern of flowering-genes in buds from on (fully loaded) and off (without fruits) trees revealed that homologues of FLOWERING LOCUS T (CiFT), TWIN SISTER OF FT (TSF), APETALA1 (CsAP1) and LEAFY (CsLFY) were negatively affected by fruit load. CiFT and TSF activities showed a marked increase in buds from off trees through the study period (ten-fold in November). By contrast, expression of the homologues of the flowering inhibitors of TERMINAL FLOWER 1 (CsTFL), TERMINAL FLOWER 2 (TFL2) and FLOWERING LOCUS C (FLC) was generally lower in off trees. Regarding floral identity genes, the increase in CsAP1 expression in off trees was much greater in buds than in leaves, and significant variations in CsLFY expression (approx. 20 %) were found only in February. Defoliation experiments further revealed that the absence of leaves completely abolished blossoming and severely affected the expression of most of the flowering-related genes, particularly decreasing the activity of floral promoters and of CsAP1 at the induction stage.
These results suggest that the presence of fruit affects flowering by greatly altering gene-expression not only at the leaf but also at the meristem level. Although leaves are required for flowering to occur, their absence strongly affects the activity of floral promoters and identity genes.
Alternate bearing; AP1; citrus; flowering; FT; FD; FLC; LFY; SOC1; TFL1; TFL2; TSF
Background and Aims
Investigating intraspecific karyotypic and genetic variations jointly can provide unique insights into how historical, ecological and cytogenetic factors influence microevolution. A coastal herb, Lysimachia mauritiana, exhibits extensive karyotypic polymorphism and displays a complex cytogeographic pattern across the Ryukyus. To explore whether a similar degree of chromosomal variation exists south of the Ryukyus, and in an attempt to ascertain the mechanisms that may have generated the patterns, comprehensive sampling was conducted in Taiwan.
Karyotypes were analysed at mitotic metaphase for 550 individuals from 42 populations throughout Taiwan Proper and its adjacent islands. In addition, genetic variation was estimated using 12 allozymes (21 loci) of 314 individuals sampled from 12 localities.
Four chromosome numbers and eight cytotypes, including four endemic cytotypes, were detected. Cytotype distributions were highly structured geographically, with single cytotypes present in most populations and four major cytotypes dominating the north, east and south of Taiwan and the Penghu Archipelago. Allozyme variation was very low and F-statistics indicated an extremely high level of population differentiation, implying limited gene flow among populations. Cluster analysis of allozyme variation uncovered four geographic groups, each corresponding perfectly to the four dominant cytotypes. The geographic structure of cytotype distribution and allozyme variation probably resulted from severe genetic drift triggered by genetic bottlenecks, suggesting that Taiwanese populations were likely to be derived from four independent founder events. In the few localities with multiple cytotypes, cytogeographic patterns and inferences of chromosomal evolution revealed a trend of northward dispersal, consistent with the course of the Kuroshio Current that has been influential in shaping the coastal biota of the region.
The data elucidate the patterns of colonization and the effects of the Kuroshio Current on the distribution of L. mauritiana in Taiwan. These inferences are highly relevant to other coastal plant species in the region and will stimulate further studies.
Cytogeography; cytotype; Kuroshio Current; Lysimachia mauritiana; population genetic structure; sea dispersal; Taiwan
Background and Aims
Knowledge of those traits that vary with latitude should be helpful in predicting how they may evolve locally under climate change. In the sea beet Beta vulgaris ssp. maritima, seed dormancy largely controls the timing of germination, is highly heritable and varies geographically; it is therefore thought to be selected by climate. The aim here was to characterize the variation in seed dormancy among sea beet populations across the French distribution area, as well as the ecological factors in situ that are correlated with and that could therefore select for seed dormancy. The relative importance of genetic inheritance vs. non-genetic variation is also evaluated.
The proportions of dormant seeds from 85 natural populations encompassing different climates over the whole French distribution area were measured under controlled conditions. Germination phenology was observed in a common garden experiment. Dormancy variation of seeds collected in situ was compared with that of seeds collected on plants grown in the greenhouse.
The proportions of dormant seeds in the greenhouse were highly variable, covering almost the entire range from 0 to 1, and followed a geographical pattern from lower dormancy at high latitudes to high dormancy at low latitudes. The distribution of dormancy was positively correlated with yearly temperatures, especially summer temperatures. Minimum temperatures in winter did not significantly explain the trait variation. The genetic component of the total variation was significant and is probably completed by an important adjustment to the local conditions brought about by maternal adaptive phenotypic plasticity.
Dormancy in sea beet could be interpreted as a way to limit summer germination and spread germination over the first autumn and spring or following autumns. This highly heritable trait has the potential to evolve in the relatively near future because of climate change.
Beta vulgaris ssp. maritima; trait distribution; seed dormancy; germination phenology; life history; ecological factors; seasons; climatic factors; latitudinal gradient; climate change
Background and Aims
In mountain plant populations, local adaptation has been described as one of the main responses to climate warming, allowing plants to persist under stressful conditions. This is especially the case for marginal populations at their lowest elevation, as they are highly vulnerable. Adequate levels of genetic diversity are required for selection to take place, while high levels of altitudinal gene flow are seen as a major limiting factor potentially precluding local adaptation processes. Thus, a compromise between genetic diversity and gene flow seems necessary to guarantee persistence under oncoming conditions. It is therefore critical to determine if gene flow occurs preferentially between mountains at similar altitudinal belts, promoting local adaptation at the lowest populations, or conversely along altitude within each mountain.
Microsatellite markers were used to unravel genetic diversity and population structure, inbreeding and gene flow of populations at two nearby altitudinal gradients of Silene ciliata, a Mediterranean high-mountain cushion plant.
Genetic diversity and inbreeding coefficients were similar in all populations. Substantial gene flow was found both along altitudinal gradients and horizontally within each elevation belt, although greater values were obtained along altitudinal gradients. Gene flow may be responsible for the homogeneous levels of genetic diversity found among populations. Bayesian cluster analyses also suggested that shifts along altitudinal gradients are the most plausible scenario.
Past population shifts associated with glaciations and interglacial periods in temperate mountains may partially explain current distributions of genetic diversity and population structure. In spite of the predominance of gene flow along the altitudinal gradients, local genetic differentiation of one of the lower populations together with the detection of one outlier locus might support the existence of different selection forces at low altitudes.
Gene flow; genetic variation; glacial refuge; local adaptation; mountain plant; altitudinal range; Silene ciliata; Caryophyllaceae
Background and Aims
The holoparasitic flowering plant Balanophora displays extreme floral reduction and was previously found to have enormous rate acceleration in the nuclear 18S rDNA region. So far, it remains unclear whether non-ribosomal, protein-coding genes of Balanophora also evolve in an accelerated fashion and whether the genes with high substitution rates retain their functionality. To tackle these issues, six different genes were sequenced from two Balanophora species and their rate variation and expression patterns were examined.
Sequences including nuclear PI, euAP3, TM6, LFY and RPB2 and mitochondrial matR were determined from two Balanophora spp. and compared with selected hemiparasitic species of Santalales and autotrophic core eudicots. Gene expression was detected for the six protein-coding genes and the expression patterns of the three B-class genes (PI, AP3 and TM6) were further examined across different organs of B. laxiflora using RT-PCR.
Balanophora mitochondrial matR is highly accelerated in both nonsynonymous (dN) and synonymous (dS) substitution rates, whereas the rate variation of nuclear genes LFY, PI, euAP3, TM6 and RPB2 are less dramatic. Significant dS increases were detected in Balanophora PI, TM6, RPB2 and dN accelerations in euAP3. All of the protein-coding genes are expressed in inflorescences, indicative of their functionality. PI is restrictively expressed in tepals, synandria and floral bracts, whereas AP3 and TM6 are widely expressed in both male and female inflorescences.
Despite the observation that rates of sequence evolution are generally higher in Balanophora than in hemiparasitic species of Santalales and autotrophic core eudicots, the five nuclear protein-coding genes are functional and are evolving at a much slower rate than 18S rDNA. The mechanism or mechanisms responsible for rapid sequence evolution and concomitant rate acceleration for 18S rDNA and matR are currently not well understood and require further study in Balanophora and other holoparasites.
Balanophora; Balanophoraceae; B-class genes; LFY; RPB2; mitochondrial matR; substitution rate; phylogeny; Santalales; parasitic plants.
Background and Aims
Heterostyly is a floral polymorphism that has fascinated evolutionary biologists since Darwin's seminal studies on primroses. The main morphological characteristic of heterostyly is the reciprocal placement of anthers and stigmas in two distinct (distyly) floral morphs. Variation in the degree of intermorph sexual reciprocity is relatively common and known to affect patterns of pollen transfer within species. However, the partitioning of sexual organ reciprocity within and between closely related species remains unknown. This study aimed at testing whether intermorph sexual reciprocity differs within vs. between primrose species that hybridize in nature and whether the positions of sexual organs are correlated with other floral traits.
Six floral traits were measured in both floral morphs of 15 allopatric populations of Primula elatior, P. veris and P. vulgaris, and anther–stigma reciprocity was estimated within and between species. A combination of univariate and multivariate approaches was used to test whether positions of reproductive organs were less reciprocal between than within species, to assess correlations between sexual organ positions and other corolla traits, and to quantify differences between morphs and species.
The three species were morphologically well differentiated in most floral traits, except that P. veris and P. vulgaris did not differ significantly in sexual organ positions. Overall, lower interspecific than intraspecific sexual organ reciprocity was detected. This decrease was marked between P. elatior and P. vulgaris, intermediate and variable between P. elatior and P. veris, but negligible between P. veris and P. vulgaris.
Differences in anther and stigma heights between the analysed primrose species were of the same magnitude or larger than intraspecific differences that altered pollen flow within other heterostylous systems. Therefore, it is possible to suggest that considerable reductions of sexual organ reciprocity between species may lower interspecific pollen flow, with potential effects on reproductive isolation.
reciprocal herkogamy; sexual organ reciprocity; Primula; primrose; distyly; heterostyly; floral morphology; hybridization; reproductive isolation; pollen flow; pre-mating barriers; speciation
Background and Aims
Prolonged storage generally reduces seed viability and vigour, although the rate of deterioration varies among species and environmental conditions. Here, we suggest a possible ageing molecular marker: At3g08030 mRNA. At3g08030 is a member of the DUF642 highly conserved family of cell-wall-associated proteins that is specific for spermatophytes.
At3g08030 expression was performed by RT-PCR and qRT-PCR analysis in seed samples differing in their rate of germination and final germination following a matrix priming and/or controlled deterioration (rapid ageing) treatment.
The At3g08030 gene transcript was present during the entire Arabidopsis thaliana plant life cycle and in seeds, during maturation, the ripening period and after germination. Matrix priming treatment increased the rate of germination of control seeds and seeds aged by controlled deterioration. Priming treatments also increased At3g08030 expression. To determine whether the orthologues of this gene are also age markers in other plant species, At3g08030 was cloned in two wild species, Ceiba aesculifolia and Wigandia urens. As in A. thaliana, the At3g08030 transcript was not present in aged seeds of the tested species but was present in recently shed seeds. A reduction in germination performance of the aged seeds under salt stress was determined by germination assays.
At3g08030 mRNA detection in a dry seed lot has potential for use as a molecular marker for germination performance in a variety of plant species.
Seed ageing; molecular marker; At3g08030; DUF642 gene family; Arabidopsis thaliana; Ceiba aesculifolia; Wigandia urens
Background and Aims
Waxy proteins are responsible for amylose synthesis in wheat seeds, being encoded by three waxy genes (Wx-A1, Wx-B1 and Wx-D1) in hexaploid wheat. In addition to their role in starch quality, waxy loci have been used to study the phylogeny of wheat. The origin of European spelt (Triticum aestivum ssp. spelta) is not clear. This study compared waxy gene sequences of a Spanish spelt collection with their homologous genes in emmer (T. turgidum ssp. dicoccum), durum (T. turgidum ssp. durum) and common wheat (T. aestivum ssp. aestivum), together with other Asian and European spelt that could be used to determine the origin of European spelt.
waxy genes were amplified and sequenced. Geneious Pro software, DNAsp and MEGA5 were used for sequence, nucleotide diversity and phylogenetic analysis, respectively.
Three, four and three new alleles were described for the Wx-A1, Wx-B1 and Wx-D1 loci, respectively. Spelt accessions were classified into two groups based on the variation in Wx-B1, which suggests that there were two different origins for the emmer wheat that has been found to be part of the spelt genetic make-up. One of these groups was only detected in Iberian material. No differences were found between the rest of the European spelt and the Asiatic spelt, which suggested that the Iberian material had a different origin from the other spelt sources.
The results suggested that the waxy gene variability present in wheat is undervalued. The evaluation of this variability has permitted the detection of ten new waxy alleles that could affect starch quality and thus could be used in modern wheat breeding. In addition, two different classes of Wx-B1 were detected that could be used for evaluating the phylogenetic relationships and the origins of different types of wheat.
Wheat; Triticum aestivum ssp. spelta; molecular characterization; phylogeny; spelt origin; waxy genes
Background and Aims
The competition–colonization trade-off theory postulates that the competitive and colonizing abilities of organisms are negatively related; this trade-off has been proposed as a major force in the maintenance of diversity. In plants, the competition–colonization trade-off is often considered to result from variation in resource partitioning, thus generating heavy competitive (non-dispersing) seeds and light (dispersing) non-competitive seeds. Here, the possibility is explored that early germination provides a competitive advantage, thus mediating competitive interactions.
Using eight populations of the heterocarpic species Crepis sancta (Asteraceae), the possibility was tested that dispersing and non-dispersing achenes differ in germination timing, and the impact of early germination on individual fitness components was analysed in the context of intraspecific competition. To evaluate whether seed reserve varies among achene types, endosperm size was also measured by analysing photographs of cross-sections taken under a binocular microscope.
Key Results and Conclusions
The results show that non-dispersing achenes germinated 4 d earlier (on average) than dispersing achenes. It is also shown that early germination provides a positive advantage for the survival and final biomass of individuals, a pattern that was consistent over the eight populations and independent of achene type. Dispersing and non-dispersing achenes did not differ in terms of seed reserve (endosperm size). It is proposed that germination phenology may mediate the competition–colonization trade-off in Crepis sancta and the evolutionary significance of this phenomenon is discussed.
Competition–colonization trade-off; germination timing; dispersal; seed heteromorphism; Crepis sancta; Asteraceae
Grasslands are a major part of the global ecosystem, covering 37 % of the earth's terrestrial area. For a variety of reasons, mostly related to overgrazing and the resulting problems of soil erosion and weed encroachment, many of the world's natural grasslands are in poor condition and showing signs of degradation. This review examines their contribution to global food supply and to combating climate change.
Grasslands make a significant contribution to food security through providing part of the feed requirements of ruminants used for meat and milk production. Globally, this is more important in food energy terms than pig meat and poultry meat. Grasslands are considered to have the potential to play a key role in greenhouse gas mitigation, particularly in terms of global carbon storage and further carbon sequestration. It is estimated that grazing land management and pasture improvement (e.g. through managing grazing intensity, improved productivity, etc) have a global technical mitigation potential of almost 1·5 Gt CO2 equivalent in 2030, with additional mitigation possible from restoration of degraded lands. Milk and meat production from grassland systems in temperate regions has similar emissions of carbon dioxide per kilogram of product as mixed farming systems in temperate regions, and, if carbon sinks in grasslands are taken into account, grassland-based production systems can be as efficient as high-input systems from a greenhouse gas perspective.
Grasslands are important for global food supply, contributing to ruminant milk and meat production. Extra food will need to come from the world's existing agricultural land base (including grasslands) as the total area of agricultural land has remained static since 1991. Ruminants are efficient converters of grass into humanly edible energy and protein and grassland-based food production can produce food with a comparable carbon footprint as mixed systems. Grasslands are a very important store of carbon, and they are continuing to sequester carbon with considerable potential to increase this further. Grassland adaptation to climate change will be variable, with possible increases or decreases in productivity and increases or decreases in soil carbon stores.
Grasslands; climate change; food security; carbon sequestration
Background and Aims
Disturbances occur in most ecological systems, and play an important role in biological invasions. We delimit five key disturbance aspects: intensity, frequency, timing, duration and extent. Few studies address more than one of these aspects, yet interactions and interdependence between aspects may lead to complex outcomes.
In a two-cohort experimental study, we examined how multiple aspects (intensity, frequency and timing) of a mowing disturbance regime affect the survival, phenology, growth and reproduction of an invasive thistle Carduus nutans (musk thistle).
Our results show that high intensity and late timing strongly delay flowering phenology and reduce plant survival, capitulum production and plant height. A significant interaction between intensity and timing further magnifies the main effects. Unexpectedly, high frequency alone did not effectively reduce reproduction. However, a study examining only frequency and intensity, and not timing, would have erroneously attributed the importance of timing to frequency.
We used management of an invasive species as an example to demonstrate the importance of a multiple-aspect disturbance framework. Failure to consider possible interactions, and the inherent interdependence of certain aspects, could result in misinterpretation and inappropriate management efforts. This framework can be broadly applied to improve our understanding of disturbance effects on individual responses, population dynamics and community composition.
Carduus nutans; thistle; disturbance timing; frequency; intensity; invasive species; mowing; population biology
Background and Aims
Models assessing the prospects of plant species at the landscape level often focus primarily on the relationship between species dynamics and landscape structure. However, the short-term prospects of species with slow responses to landscape changes depend on the factors affecting local population dynamics. In this study it is hypothesized that large herbivores may be a major factor affecting the short-term prospects of slow-responding species in the European landscape, because large herbivores have increased in number in this region in recent decades and can strongly influence local population dynamics.
The impact of browsing by large herbivores was simulated on the landscape-level dynamics of the dry grassland perennial polycarpic herb Scorzonera hispanica. A dynamic, spatially explicit model was used that incorporated information on the location of patches suitable for S. hispanica, local population dynamics (matrices including the impact of large herbivores), initial population sizes and dispersal rate of the species. Simulations were performed relating to the prospects of S. hispanica over the next 30 years under different rates of herbivory (browsing intensity) and varying frequencies of population destruction (e.g. by human activity).
Although a high rate of herbivory was detected in most populations of S. hispanica, current landscape-level dynamics of S. hispanica were approximately in equilibrium. A decline or increase of over 20 % in the herbivory rate promoted rapid expansion or decline of S. hispanica, respectively. This effect was much stronger in the presence of population destruction.
Browsing by large herbivores can have a dramatic effect on the landscape dynamics of plant species. Changes in the density of large herbivores and the probability of population destruction should be incorporated into models predicting species abundance and distribution.
Bromion erecti; grazing; landscape-level modelling; large ungulates; roe deer
Background and Aims
The enemy release hypothesis assumes that invasive plants lose their co-evolved natural enemies during introduction into the new range. This study tested, as proposed by the evolution of increased competitive ability (EICA) hypothesis, whether escape from enemies results in a decrease in defence ability in plants from the invaded range. Two straightforward aspects of the EICA are examined: (1) if invasives have lost their enemies and their defence, they should be more negatively affected by their full natural pre-invasion herbivore spectrum than their native conspecifics; and (2) the genetic basis of evolutionary change in response to enemy release in the invasive range has not been taken sufficiently into account.
Lythrum salicaria (purple loosestrife) from several populations in its native (Europe) and invasive range (North America) was exposed to all above-ground herbivores in replicated natural populations in the native range. The experiment was performed both with plants raised from field-collected seeds as well as with offspring of these where maternal effects were removed.
Absolute and relative leaf damage was higher for introduced than for native plants. Despite having smaller height growth rate, invasive plants attained a much larger final size than natives irrespective of damage, indicating large tolerance rather than effective defence. Origin effects on response to herbivory and growth were stronger in second-generation plants, suggesting that invasive potential through enemy release has a genetic basis.
The findings support two predictions of the EICA hypothesis – a genetically determined difference between native and invasive plants in plant vigour and response to enemies – and point to the importance of experiments that control for maternal effects and include the entire spectrum of native range enemies.
Biological control; field experiment; herbivory; purple loosestrife; enemy release; EICA hypothesis; invasion; Lythrum salicaria
Background and Aims
There is currently much speculation about the role of epigenetic variation as a determinant of heritable variation in ecologically important plant traits. However, we still know very little about the phenotypic consequences of epigenetic variation, in particular with regard to more complex traits related to biotic interactions.
Here, a test was carried out to determine whether variation in DNA methylation alone can cause heritable variation in plant growth responses to jasmonic acid and salicylic acid, two key hormones involved in induction of plant defences against herbivores and pathogens. In order to be able to ascribe phenotypic differences to epigenetic variation, the hormone responses were studied of epigenetic recombinant inbred lines (epiRILs) of Arabidopsis thaliana – lines that are highly variable at the level of DNA methylation but nearly identical at the level of DNA sequence.
Significant heritable variation was found among epiRILs both in the means of phenotypic traits, including growth rate, and in the degree to which these responded to treatment with jasmonic acid and salicylic acid. Moreover, there was a positive epigenetic correlation between the responses of different epiRILs to the two hormones, suggesting that plant responses to herbivore and pathogen attack may have a similar molecular epigenetic basis.
This study demonstrates that epigenetic variation alone can cause heritable variation in, and thus potentially microevolution of, plant responses to defence hormones. This suggests that part of the variation of plant defences observed in natural populations may be due to underlying epigenetic, rather than entirely genetic, variation.
Arabidopsis thaliana; DNA methylation; epigenetic recombinant inbred line; epiRIL; growth rate; induced defence; jasmonic acid; salicylic acid
Plant facilitation occurs when the presence of a plant (i.e. a nurse plant) modifies the environment, making it more favourable for the establishment and survival of other species (i.e. facilitated plants), which can germinate and grow nearby. Facilitative associations can be maintained or turned into competition as the facilitated seedling grows. According to the competition-relatedness hypothesis that suggests that closely related species tend to compete more, facilitation turns into competition between phylogenetically close species. However, some examples of facilitation between congeneric species, which are supposed to be closely related species, have been found in nature.
In this work, some examples of congeneric facilitation and subsequent coexistence are reviewed and an attempt is made to explain those exceptions to the competition-relatedness hypothesis.
Two mechanisms are proposed that can switch the facilitation–competition balance: trait divergence and indirect interactions. When traits have diverged within the genus, the niche overlap is reduced and competition relaxed, thus allowing the coexistence of congeneric species. The presence of third interplayers (mycorrhizal fungi, seed dispersers, pollinators or pathogens) participating in the interaction between plants can alleviate the competition or enhance the reproduction and allow the coexistence of species that could not coexist in their absence.
Associational defences; competition; facilitation; indirect interactions; mycorrhizal networks; phylogenetic relatedness; pollination; seed dispersal; trait divergence
Background and Aims
Genome size is known to be correlated with a number of phenotypic traits associated with cell sizes and cell-division rates. Genome size was therefore used as a proxy for them in order to assess how common plant traits such as height, specific leaf area and seed size/number predict species regional abundance. In this study it is hypothesized that if there is residual correlation between genome size and abundance after these traits are partialled out, there must be additional ecological effects of cell size and/or cell-division rate.
Variation in genome size, plant traits and regional abundance were examined in 436 herbaceous species of central European flora, and relationships were sought for among these variables by correlation and path analysis.
Species regional abundance was weakly but significantly correlated with genome size; the relationship was stronger for annuals (R2 = 0·145) than for perennials (R2 = 0·027). In annuals, genome size was linked to abundance via its effect on seed size, which constrains seed number and hence population growth rate. In perennials, it weakly affected (via height and specific leaf area) competitive ability. These relationships did not change qualitatively after phylogenetic correction. In both annuals and perennials there was an unresolved effect of genome size on abundance.
The findings indicate that additional predictors of regional abundance should be sought among variables that are linked to cell size and cell-division rate. Signals of these cell-level processes remain identifiable even at the landscape scale, and show deep differences between perennials and annuals. Plant population biology could thus possibly benefit from more systematic use of indicators of cell-level processes.
Annuals; C-value; functional traits; genome size; LEDA traitbase; native herbaceous plant species; path analysis; phylogenetic correction; perennials
Background and Aims
Gene flow by seed and pollen largely shapes the genetic structure within and among plant populations. Seed dispersal is often strongly spatially restricted, making gene flow primarily dependent on pollen dispersal within and into populations. To understand distance-dependent pollination success, pollen dispersal and gene flow were studied within and into a population of the alpine monocarpic perennial Campanula thyrsoides.
A paternity analysis was performed on sampled seed families using microsatellites, genotyping 22 flowering adults and 331 germinated offspring to estimate gene flow, and pollen analogues were used to estimate pollen dispersal. The focal population was situated among 23 genetically differentiated populations on a subalpine mountain plateau (<10 km2) in central Switzerland.
Paternity analysis assigned 110 offspring (33·2 %) to a specific pollen donor (i.e. ‘father’) in the focal population. Mean pollination distance was 17·4 m for these offspring, and the pollen dispersal curve based on positive LOD scores of all 331 offspring was strongly decreasing with distance. The paternal contribution from 20–35 offspring (6·0–10·5 %) originated outside the population, probably from nearby populations on the plateau. Multiple potential fathers were assigned to each of 186 offspring (56·2 %). The pollination distance to ‘mother’ plants was negatively affected by the mothers' degree of spatial isolation in the population. Variability in male mating success was not related to the degree of isolation of father plants.
Pollen dispersal patterns within the C. thyrsoides population are affected by spatial positioning of flowering individuals and pollen dispersal may therefore contribute to the course of evolution of populations of this species. Pollen dispersal into the population was high but apparently not strong enough to prevent the previously described substantial among-population differentiation on the plateau, which may be due to the monocarpic perenniality of this species.
Gene flow; pollen dispersal; Campanula thyrsoides; European Alps; male mating success; monocarpic perenniality; paternity analysis; pollen analogues; pollination distance
Despite the importance of the Galápagos Islands for the development of central concepts in ecology and evolution, the understanding of many ecological processes in this archipelago is still very basic. One such process is pollination, which provides an important service to both plants and their pollinators. The rather modest level of knowledge on this subject has so far limited our predictive power on the consequences of the increasing threat of introduced plants and pollinators to this unique archipelago.
As a first step toward building a unified view of the state of pollination in the Galápagos, a thorough literature search was conducted on the breeding systems of the archipelago's flora and compiled all documented flower–visitor interactions. Based on 38 studies from the last 100 years, we retrieved 329 unique interactions between 123 flowering plant species (50 endemics, 39 non-endemic natives, 26 introduced and eight of unknown origin) from 41 families and 120 animal species from 13 orders. We discuss the emergent patterns and identify promising research avenues in the field.
Although breeding systems are known for <20 % of the flora, most species in our database were self-compatible. Moreover, the incidence of autogamy among endemics, non-endemic natives and alien species did not differ significantly, being high in all groups, which suggests that a poor pollinator fauna does not represent a constraint to the integration of new plant species into the native communities. Most interactions detected (approx. 90 %) come from a single island (most of them from Santa Cruz). Hymenopterans (mainly the endemic carpenter bee Xylocopa darwinii and ants), followed by lepidopterans, were the most important flower visitors. Dipterans were much more important flower visitors in the humid zone than in the dry zone. Bird and lizard pollination has been occasionally reported in the dry zone. Strong biases were detected in the sampling effort dedicated to different islands, time of day, focal plants and functional groups of visitors. Thus, the existing patterns need to be confronted with new and less biased data. The implementation of a community-level approach could greatly increase our understanding of pollination on the islands and our ability to predict the consequences of plant invasions for the natural ecosystems of the Galápagos.
Galápagos; flower visitation; mutualistic interactions; oceanic islands; plant breeding systems; plant–animal interactions; pollination networks
Background and aims
Species in plant communities segregate along fine-scale hydrological gradients. Although this phenomenon is not unique to fynbos, this community regenerates after fire and therefore provides an opportunity to study the ecological genesis of hydrological niche segregation.
Following wildfires at two field sites where we had previously mapped the vegetation and monitored the hydrology, seeds were moved experimentally in >2500 intact soil cores up and down soil-moisture gradients to test the hypothesis that hydrological niche segregation is established during the seedling phase of the life cycle. Seedling numbers and growth were then monitored and they were identified using DNA bar-coding, the first use of this technology for an experiment of this kind.
At the site where niche segregation among Restionaceae had previously been found, the size of seedlings was significantly greater, the wetter the location into which they were moved, regardless of the soil moisture status of their location of origin, or of the species. Seedling weight was also significantly greater in a competition treatment where the roots of other species were excluded. No such effects were detected at the control site where niche segregation among Restionaceae was previously found to be absent.
The finding that seedling growth on hydrological gradients in the field is affected by soil moisture status and by root competition shows that hydrological niche segregation could potentially originate in the seedling stage. The methodology, applied at a larger scale and followed-through for a longer period, could be used to determine whether species are differently affected by soil moisture.
Translocation experiment; seedling regeneration; fire; soil-moisture gradient; hydrological niche; root competition; DNA bar-coding; regeneration niche
Background and Aims
Differences in competitive ability between the sexes of dioecious plants are expected as a result of allocation trade-offs associated with sex-differential reproductive costs. However, the available data on competitive ability in dioecious plants are scarce and contradictory. In this study sexual competition was evaluated using the dioecious plant Antennaria dioica in a common garden transplantation experiment.
Male and female plants were grown for 3 years either in isolation, or in competition with a plant of the same sex or the opposite sex. Flowering phenology, sexual and asexual reproduction, plant growth, nutrient content and arbuscular mycorrhizal colonization in the roots were assessed.
Our results showed little evidence of sexual differences in competitive ability. Both sexes suffered similarly from competition, and competitive effects were manifested in some traits related to fitness but not in others. Survival was unaffected by competition, but competing plants reduced their vegetative growth and reproductive investment compared with non-competing plants. In addition, differences in sexual competitive ability were observed in relation to flowering frequency, an important life history trait not reported in previous studies.
The findings indicate that female and male A. dioica plants possess similar intersexual competitive abilities which may be related to the similar costs of reproduction between sexes in this species. Nevertheless, intrasexual competition is higher in females, giving support for asymmetric niche segregation between the sexes.
Antennaria dioica; competition; dioecy; niche segregation; sexual dimorphism
Background and aims
Changes in the sex allocation (i.e. in pollen versus seed production) of hermaphroditic plants often occur in response to the environment. In some homosporous ferns, gametophytes choose their gender in response to chemical cues sent by neighbours, such that spores develop as male gametophytes if they perceive a female or hermaphrodite nearby. Here it is considered whether a similar process might occur in the androdioecious angiosperm species Mercurialis annua, in which males co-occur with hermaphrodites; previous work on a Spanish population of M. annua found that individuals were more likely to develop as males at high density.
Using a novel approach to treat plants with leachate from pots containing males or hermaphrodites of M. annua, the hypothesis that individuals assess their mating opportunities, and adjust their sex expression accordingly, was tested through an exchange of chemical cues through the soil.
For the population under study, from Morocco, no evidence was found for soil-signal-dependent sex expression: neither sex ratios nor sex allocation differed among experimental treatments.
The results imply either that the Moroccan population under study behaves differently from that previously studied in Spain (pointing to potential geographical variation in plasticity for sex expression), or that our method failed to capture the signals used by M. annua for adjustment of sex expression.
Androdioecy; environmental sex determination; environmental cues; hermaphroditism; phenotypic plasticity