Polyploid speciation did not confer instant reproductive isolation in Capsella (Brassicaceae)

Polyploid formation is a major mode of sympatric speciation in flowering plants. Unlike other speciation processes, polyploidization is often assumed to confer instant reproductive isolation. Shared polymorphism across ploidy levels has therefore often been attributed to multiple polyploid origins, whereas the alternative hypothesis of introgressive hybridization has rarely been rigorously tested. Here, we sequence 12 nuclear loci representing 6 genes duplicated by polyploidy in 92 accessions of the tetraploid Capsella bursa-pastoris together with the corresponding loci in 21 accessions of its close diploid relative Capsella rubella. In C. bursa-pastoris accessions from western Eurasia, where the 2 species occur in partial sympatry, we find higher levels of nucleotide diversity than in accessions from eastern Eurasia, where C. rubella does not grow. Furthermore, haplotypes are shared across ploidy levels at 4 loci in western but not in eastern Eurasia. We test whether haplotype sharing is due to retention of ancestral polymorphism or due to hybridization and introgression using a coalescent-based isolation-with-migration model. In western but not in eastern Eurasia, there is evidence for unidirectional gene flow from C. rubella to C. bursa-pastoris. An independent estimate of the timing of dispersal of C. bursa-pastoris to eastern Eurasia indicates that it probably predated introgression. Our results show that polyploid speciation need not result in immediate and complete reproductive isolation, that postpolyploidization hybridization and introgression can contribute significantly to genetic variation in a newly formed polyploid, and that divergence population genetic analysis constitutes a powerful way of testing hypotheses on polyploid speciation.     

Maternal environmental effects on the phenotypic responses of the twining vine Ipomoea purpurea to support availability

The presence of physical support elicits a number of morphological changes in the shoot of the common morning glory Ipomoea purpurea , including a shortening of internodes and petioles and a thickening of the main stem. Working with experimentally supported and non-supported plants of I . purpurea , I tested the existence of maternal environmental effects of physical support in this twining vine. I evaluated whether the offspring of supported plants differed from the offspring of non-supported plants in a number of morphological and reproductive characters. Stem diameter was the only shoot trait that showed a significant effect of the maternal environment (support). The stems of the progeny of supported mother plants were thicker than the stems of the progeny of non-supported mother plants. This was true for both supported and non-supported progeny. Stem diameter, however, was not significantly related to plant fitness (seed number) in supported or non-supported progeny plants. The maternal environment did not affect the magnitude of the phenotypic responses to support of shoot traits in the progeny plants. There were no maternal environmental effects of physical support on the proportion of flowering plants at week 10 in both non-supported and supported progeny. Likewise, the presence of physical support in the maternal environment did not affect reproductive traits (seed number, seed size, percentage of reproductive biomass) in supported and non-supported progeny plants. Finally, the relationship between seed size and seed number was affected by the maternal support environment. The progeny of supported mother plants showed a significantly negative association (trade-off) between seed size and number, whereas such a trade-off was not observed in the progeny of non-supported plants. This was true for both supported and non-supported progeny.     

Differential expression of genes important for adaptation in Capsella bursa-pastoris (Brassicaceae)

Understanding the genetic basis of natural variation is of primary interest for evolutionary studies of adaptation. In Capsella bursa-pastoris, a close relative of Arabidopsis (Arabidopsis thaliana), variation in flowering time is correlated with latitude, suggestive of an adaptation to photoperiod. To identify pathways regulating natural flowering time variation in C. bursa-pastoris, we have studied gene expression differences between two pairs of early- and late-flowering C. bursa-pastoris accessions and compared their response to vernalization. Using Arabidopsis microarrays, we found a large number of significant differences in gene expression between flowering ecotypes. The key flowering time gene FLOWERING LOCUS C (FLC) was not differentially expressed prior to vernalization. This result is in contrast to those in Arabidopsis, where most natural flowering time variation acts through FLC. However, the gibberellin and photoperiodic flowering pathways were significantly enriched for gene expression differences between early- and late-flowering C. bursa-pastoris. Gibberellin biosynthesis genes were down-regulated in late-flowering accessions, whereas circadian core genes in the photoperiodic pathway were differentially expressed between early- and late-flowering accessions. Detailed time-series experiments clearly demonstrated that the diurnal rhythm of CIRCADIAN CLOCK-ASSOCIATED1 (CCA1) and TIMING OF CAB EXPRESSION1 (TOC1) expression differed between flowering ecotypes, both under constant light and long-day conditions. Differential expression of flowering time genes was biologically validated in an independent pair of flowering ecotypes, suggesting a shared genetic basis or parallel evolution of similar regulatory differences. We conclude that genes involved in regulation of the circadian clock, such as CCA1 and TOC1, are strong candidates for the evolution of adaptive flowering time variation in C. bursa-pastoris.     

Details of local dispersion improve the fit of neighborhood competition models

I performed a series of greenhouse experiments to explore how patterns in the dispersion of local competitors affect the reproductive performance of Capsella bursa-pastoris, Poa annua and Senecio vulgaris. I manipulated the density and relative frequency of competitors in each of three concentric rings surrounding a central plant, thereby creating a variety patterns by which local competitors were distributed. Neighborhood competition models were used to predict the seed output of these central plants. For both Senecio vulgaris and Capsella bursa-pastoris, I found that models which incorporated the dispersion of competitors, as well as the relative emergence date of plants, performed substantially better than those that considered only the distance between the central plant and each of its competitors. I was unable to measure the seed output of Poa annua but neither emergence data nor the dispersion of competitors were important in determining its final dry-weight. Present address: Department of Biology, Box 1137, Washington University, 1 Brookings Drive, St. Louis, MO 63130, USA     

Host responses in life-history traits and tolerance to virus infection in Arabidopsis thaliana

Knowing how hosts respond to parasite infection is paramount in understanding the effects of parasites on host populations and hence host-parasite co-evolution. Modification of life-history traits in response to parasitism has received less attention than other defence strategies. Life-history theory predicts that parasitised hosts will increase reproductive effort and accelerate reproduction. However, empirical analyses of these predictions are few and mostly limited to animal-parasite systems. We have analysed life-history trait responses in 18 accessions of Arabidopsis thaliana infected at two different developmental stages with three strains of Cucumber mosaic virus (CMV). Accessions were divided into two groups according to allometric relationships; these groups differed also in their tolerance to CMV infection. Life-history trait modification upon virus infection depended on the host genotype and the stage at infection. While all accessions delayed flowering, only the more tolerant allometric group modified resource allocation to increase the production of reproductive structures and progeny, and reduced the length of reproductive period. Our results are in agreement with modifications of life-history traits reported for parasitised animals and with predictions from life-history theory. Thus, we provide empirical support for the general validity of theoretical predictions. In addition, this experimental approach allowed us to quantitatively estimate the genetic determinism of life-history trait plasticity and to evaluate the role of life-history trait modification in defence against parasites, two largely unexplored issues.     

Genetic structure among arable populations of Capsella bursa‐pastoris is linked to functional traits and in‐field conditions

Wild arable plants can be an economic burden but they also support diverse arable food webs and contribute to valuable ecosystem functions. These benefits may have been compromised over recent decades by declining weed diversity. The decline in wild arable plant diversity has been viewed predominantly in terms of species shifts a view that ignores the genetic and functional variation existing within species and the impact on ecological and evolutionary processes which this may have. To examine within‐species diversity, ISSR markers were used in parallel with environmental and phenotypic characterisation, to investigate the population structure and diversity of Capsella bursa‐pastoris (shepherd's purse) from arable fields in the UK. Analysis of 338 ISSR products for 109 individuals from 51 accessions obtained from the seed banks of 33 arable fields showed that in‐field populations of shepherd's purse were genetically differentiated between individuals, and among accessions and fields. In addition, cluster analysis identified three genetically distinct regional‐scale populations. Phenotypic variation was present at all scales of genetic differentiation, including the regional scale where populations differed in their key life‐history traits: flowering time, fecundity and dormancy. Genetic drift is proposed as a contributor to differentiation among genetically isolated but locally co‐occurring accessions. In addition, the genetic and phenotypic variation in shepherd's purse exhibited large scale, spatial trends and showed statistically significant associations with cropping intensity and soil‐pH. These results suggest that adaptation as a result of selection by cropping practise and soil‐pH has played a role in the ability of shepherd's purse to colonise and persist in arable fields.     

Variability in reproductive traits in Jatropha curcas L. accessions during early developmental stages under warm subtropical conditions

Variability in floral, fruit, and seed characteristics, and oil content of 15 accession of Jatropha curcas during early development were assessed during two flowering periods in south Florida subtropical climate. The two flowering periods had leaf flushing in March. Field evaluation using 18 quantitative traits showed significant variation among accessions. The number of female flowers and female : male flower ratio ranged from 1 to 15 and 1 : 8.8 to 1 : 67.8, respectively. Fruit set by natural pollination was 89 and 66% during the first (1st) and second (2nd) flowering periods, respectively. A higher number of female‐type inflorescences were observed during summer. There were significant differences in seed traits, except for number of seeds per fruit. Accession TREC 31 had the highest individual seed dry weight and 100‐seed weight (0.83 g and 79.7 g, respectively). The oil content varied from 19.30% to 35.62%. Seed dry weight had positive correlation with seed fresh weight, seed length, seed thickness, seed width, and 100‐seed weight, but negative correlation with oil content. Based on the cluster analysis using 15 morphological traits, jatropha accessions were grouped into five main clusters and accessions from different geographic regions grouped together in a cluster. Principal component analyses (PCA) revealed morphological variation. The first three components explained 73.5% of the total variation and seed dry weight, 100‐seed weight, total flowers per inflorescence, male flowers per inflorescence and fruit set can be used to distinguish accessions. The PCA also indicated that flowering traits were more influenced by seed origin while seed traits were affected by flowering spans. Although evaluations were performed in plants during the juvenile phase, accessions TREC 31 and TREC 55 had superior averages for almost all characters evaluated. These results provide a preliminary assessment of the high variability in jatropha accessions evaluated and their potential for use in breeding and genetic improvement programs.     

Intrageneric phylogeny of Capsella (Brassicaceae) and the origin of the tetraploid C. bursa-pastoris based on chloroplast and nuclear DNA sequences

Polyploidization, often accompanied by hybridization, has been of major importance in flowering plant evolution. Here we investigate the importance of these processes for the evolution of the tetraploid crucifer Capsella bursa-pastoris using DNA sequences from two chloroplast loci as well as from three nuclear low-copy genes. The near-absence of variation at the C. bursa-pastoris chloroplast markers suggests a single and recent origin of the tetraploid. However, despite supporting a single phylogeny, chloroplast data indicate that neither of the extant Capsella diploids is the maternal parent of the tetraploid. Combined with data from the three nuclear loci, our results do not lend support to previous hypotheses on the origin of C. bursa-pastoris as an allopolyploid between the diploids C. grandiflora and C. rubella or an autopolyploid of C. grandiflora. Nevertheless, for each locus, some of the C. bursa-pastoris accessions harbored C. rubella alleles, indicating that C. rubella contributed to the gene pool of C. bursa-pastoris, either through allopolyploid speciation or, more likely, through hybridization and introgression. To our knowledge, this study is the first of a wild, nonmodel plant genus that uses a combination of chloroplast and multiple low-copy nuclear loci for phylogenetic inference of polyploid evolution.     

Bayesian inference of evolutionary history from chloroplast microsatellites in the cosmopolitan weed Capsella bursa-pastoris (Brassicaceae)

Besides showing an extraordinary degree of phenotypic variability, Capsella bursa-pastoris (Brassicaceae) is also one of the world's most common plant species and a serious weed in many countries. We have employed a coalescent-based Bayesian analysis of chloroplast microsatellite data to infer demographic and evolutionary parameters of this species. Two different demographic models applied to data from seven chloroplast microsatellite loci among 59 accessions show that the effective population size of C. bursa-pastoris is very small indicating a rapid expansion of the species, a result that is in accordance with fossil and historical data. Against this background, analysis of flowering time variation among accessions suggests that ecotypic differentiation in flowering time has occurred recently in the species' history. Finally, our results also indicate that mononucleotide repeat loci in the chloroplast genome can deteriorate in relatively short periods of evolutionary time.     

Relationships between flowering phenology,plant size and reproductive success in shape Lotus corniculatus (Fabaceae)

Over three years the flowering phenology of individuals of Lotus corniculatus has been studied in relation to fruit set and seed predation to determine the relationships between four components of flowering time, plant size and reproductive success. Timings of first and peak flowering, and duration and synchrony of flowering differed between individuals in the same years. Between years, timing of first flowering was highly correlated for the same individuals, and was closely correlated with plant size and duration of flowering–larger plants flowered earlier and for a longer period. Peak flowering and synchrony were not correlated between-years for individuals.Fruit production and seed predation were correlated with some of the components of flowering phenology in some years, but not in others. The inconstancy of these relationships suggests that directional or stabilising selection is not acting consistently on the aspects of reproductive success studied in this work. The inconstancy of selection may result in the rather asynchronous flowering phenologies of individuals of L. corniculatus observed.We emphasize the importance of studying different components of flowering phenology in relation to individual plant size over several seasons. This work has shown that plant size not only has a direct effect on individual plant fecundity but also can influence flowering time and hence indirectly affect reproductive output.     

Population age structure and reproductive behavior of the monocarpic perennial Heracleum mantegazzianum (Apiaceae) in its native and invaded distribution ranges

Many invasive species are benign in their native region-are there interactions between their key traits and the new habitats that explain invasion success? The giant perennial herb Heracleum mantegazzianum is a problematic invader in Europe and is also naturalized in North America. We compared its population structure and reproductive behavior in the native (W. Caucasus) and invaded (Czech Republic) areas in managed (pastures) and unmanaged sites. The age structure of the populations and age at flowering were analyzed using herb-chronology, a method based on counting annual rings in the secondary xylem of roots. The species was strictly monocarpic; most plants in unmanaged sites in the invaded range flowered in the third and fourth yr (maximum 12 yr). In unmanaged habitats, plants from the native range flowered later than those from the invaded range. In both ranges, flowering was delayed in managed sites where the population density was higher and most plants flowered around the fifth year. Reproductive output of individual plants was neither related to population density nor to age at flowering. More favorable climatic conditions in the invaded region, together with increased chances for dispersal in a densely colonized central Europe, seemed to allow the massive invasion.     

Magnitude and timing of leaf damage affect seed production in a natural population of Arabidopsis thaliana (Brassicaceae)

Background

The effect of herbivory on plant fitness varies widely. Understanding the causes of this variation is of considerable interest because of its implications for plant population dynamics and trait evolution. We experimentally defoliated the annual herb Arabidopsis thaliana in a natural population in Sweden to test the hypotheses that (a) plant fitness decreases with increasing damage, (b) tolerance to defoliation is lower before flowering than during flowering, and (c) defoliation before flowering reduces number of seeds more strongly than defoliation during flowering, but the opposite is true for effects on seed size.

Methodology/Principal Findings

In a first experiment, between 0 and 75% of the leaf area was removed in May from plants that flowered or were about to start flowering. In a second experiment, 0, 25%, or 50% of the leaf area was removed from plants on one of two occasions, in mid April when plants were either in the vegetative rosette or bolting stage, or in mid May when plants were flowering. In the first experiment, seed production was negatively related to leaf area removed, and at the highest damage level, also mean seed size was reduced. In the second experiment, removal of 50% of the leaf area reduced seed production by 60% among plants defoliated early in the season at the vegetative rosettes, and by 22% among plants defoliated early in the season at the bolting stage, but did not reduce seed output of plants defoliated one month later. No seasonal shift in the effect of defoliation on seed size was detected.

Conclusions/Significance

The results show that leaf damage may reduce the fitness of A. thaliana, and suggest that in this population leaf herbivores feeding on plants before flowering should exert stronger selection on defence traits than those feeding on plants during flowering, given similar damage levels.     

Weak impact of fine‐scale landscape heterogeneity on evolutionary potential in Arabidopsis lyrata

Microhabitat heterogeneity can lead to fine‐scale local adaptation when gene flow is restricted, which may be important for the maintenance of genetic variation within populations. This study tested whether microhabitat heterogeneity was associated with trait differences in a population of Arabidopsis lyrata and studied its impact on the genetic variance–covariance (G) matrix. Maternal seed families were collected from dune tops and bottoms, two microhabitats known to vary significantly in water availability. In a common garden experiment, replicate individuals per family were raised under wet and dry conditions, and physiological, morphological and life‐history traits were assessed. Plants from the two microenvironments differed in their response to treatment in two performance components, in stomata density and most strongly in flowering time. Under wet conditions, plants originating from dune bottoms flowered 4 weeks earlier than those from dune tops. Only one of three G‐matrix comparisons revealed that habitat heterogeneity and evolutionary potential were positively linked. The number of independent trait dimensions was larger in the entire population than within subpopulations separated by microhabitat under wet conditions. However, the size of the G‐matrix was no larger in the entire population than within subpopulations separated by microhabitat, and trait correlation structure between microhabitats and treatments was not significantly different. These results indicate that fine‐scale habitat heterogeneity likely led to local adaptation, which weakly affected levels of across‐trait genetic variation.     

Production and genetic analysis of partial hybrids in intertribal crosses between Brassica species (B. rapa, B. napus) and Capsella bursa-pastoris

Capsella bursa-pastoris (L.) Medic (2n = 4x = 32) is a natural double-low (erucic acid < 1%, glucosinolates < 30 micromol/g) germplasm and shows high degree of resistance to Sclerotinia sclerotiorum. Hybridizations were carried out between two Brassica species viz. B. rapa (2n = 20) and B. napus (2n = 38) as female and C. bursa-pastoris as male parent to introduce these desirable traits into cultivated Brassica species. Majority of F(1) plants resembled female parents in morphology and only a few expressed some characters of male parent, including the white petals. Based on cytological observation of somatic cells, the F(1) plants were classified into five types: two types from the cross with B. rapa, type I had 2n = 27-29; type II had 2n = 20; three types from the crosses with B. napus, type III was haploids with 2n = 19; type IV had 2n = 29; type V had 2n = 38. One to two chromosomes of C. bursa-pastoris were detected in pollen mother cells (PMCs) of type I plant by genomic in situ hybridization (GISH), together with chromosomal segments in ovary cells and PMCs of some F1 plants. Amplified fragment length polymorphism (AFLP) bands specific for the male parent, novel for two parents and absent bands in Brassica parents were generated in majority of F1 plants, even in Brassica-types and haploids, indicating the introgressions at various levels from C. bursa-pastoris and genomic alterations following hybridization. Some Brassica-type progeny plants had reduced contents of erucic acid and glucosinolates associated with improved resistance to S. sclerotiorum. The cytological and molecular mechanisms behind these results are discussed.     

Introduced plants of Lupinus polyphyllus are larger but flower less frequently than conspecifics from the native range: Results of the first year

Introduced species, which establish in novel environments, provide an opportunity to explore trait evolution and how it may contribute to the distribution and spread of species. Here, we explore trait changes of the perennial herb Lupinus polyphyllus based on 11 native populations in the western USA and 17 introduced populations in Finland. More specifically, we investigated whether introduced populations outperformed native populations in traits measured in situ (seed mass) and under common garden conditions during their first year (plant size, flowering probability, and number of flowering shoots). We also explored whether climate of origin (temperature) influenced plant traits and quantified the degree to which trait variability was explained collectively by country and temperature as compared to other population‐level differences. Three out of four plant traits differed between the native and introduced populations; only seed mass was similar between countries, with most of its variation attributed to other sources of intraspecific variation not accounted for by country and temperature. Under common garden conditions, plants originating from introduced populations were larger than those originating from native populations. However, plants from the introduced range flowered less frequently and had fewer flowering shoots than their native‐range counterparts. Temperature of a population''s origin influenced plant size in the common garden, with plant size increasing with increasing mean annual temperature in both native and introduced populations. Our results of the first year reveal genetic basis for phenotypic differences in some fitness‐related traits between the native and introduced populations of L. polyphyllus. However, not all of these trait differences necessarily contribute to the invasion success of the species and thus may not be adaptive, which raises a question how persistent the trait differences observed in the first year are later in individuals’ life for perennial herbs.     

湖南省德夯峡谷生境种子植物功能性状多样性

为探明峡谷生境植物功能性状多样性组成基本规律,该研究以湖南省德夯峡谷1 627种种子植物为对象,选择生长型、叶型、叶级等7个营养性状以及性系统、花序类型、果实类型等6个繁殖性状为参数,建立该区域种子植物功能性状数据库并进行统计分析。结果表明：(1)受峡谷温热潮湿环境影响,德夯种子植物营养性状既有中亚热带又有南亚热带植物功能性状特点,生长型以多年生草本为主,叶性质以中小型叶、单叶、纸质、全缘、不裂、互生、两面都无毛为主,且中型叶多于小型叶。(2)德夯种子植物繁殖性状以两性花、顶生和腋生无限花序、干果、动物传播种子为主,且雌雄同株植物多于雌雄异株,表现出对峡谷生境的适应特性;花期主要集中在4~8月,果期主要集中在7~10月。研究发现,植物功能性状数据库在探寻特定环境下植物多样性组成规律时具有重要作用,值得进一步深入研究和运用。     

Seed traits are pleiotropically regulated by the flowering time gene PERPETUAL FLOWERING 1 (PEP1) in the perennial Arabis alpina

The life cycles of plants are characterized by two major life history transitions—germination and the initiation of flowering—the timing of which are important determinants of fitness. Unlike annuals, which make the transition from the vegetative to reproductive phase only once, perennials iterate reproduction in successive years. The floral repressor PERPETUAL FLOWERING 1 (PEP1), an ortholog of FLOWERING LOCUS C, in the alpine perennial Arabis alpina ensures the continuation of vegetative growth after flowering and thereby restricts the duration of the flowering episode. We performed greenhouse and garden experiments to compare flowering phenology, fecundity and seed traits between A. alpina accessions that have a functional PEP1 allele and flower seasonally and pep1 mutants and accessions that carry lesions in PEP1 and flower perpetually. In the garden, perpetual genotypes flower asynchronously and show higher winter mortality than seasonal ones. PEP1 also pleiotropically regulates seed dormancy and longevity in a way that is functionally divergent from FLC. Seeds from perpetual genotypes have shallow dormancy and reduced longevity regardless of whether they after‐ripened in plants grown in the greenhouse or in the experimental garden. These results suggest that perpetual genotypes have higher mortality during winter but compensate by showing higher seedling establishment. Differences in seed traits between seasonal and perpetual genotypes are also coupled with differences in hormone sensitivity and expression of genes involved in hormonal pathways. Our study highlights the existence of pleiotropic regulation of seed traits by hub developmental regulators such as PEP1, suggesting that seed and flowering traits in perennial plants might be optimized in a coordinated fashion.     

Impact of enhanced ultraviolet-B radiation on flower, pollen, and nectar production

Intensified ultraviolet-B radiation or UV-B (wavelengths between 280 and 320 nm) can delay flowering and diminish lifetime flower production in a few plants. Here we studied the effects of enhanced UV-B on floral traits crucial to pollination and pollinator reproduction. We observed simultaneous flowering responses of a new crop plant, Limnanthes alba (Limnathaceae), and a wildflower, Phacelia campanularia (Hydrophyllaceae), to five lifetime UV-B dosages ranging between 2.74 and 15.93 kJ·m·d. Floral traits known to link plant pollination with bee host preference, host fidelity and larval development were measured. Intensified UV-B had no overall effect on nectar and pollen production of L. alba and P. campanularia flowers. A quadratic relationship between UV-B and nectar sugar production occurred in P. campanularia and showed that even subambient UV-B dosages can be deleterious for a floral trait. Other floral responses to UV-B were more dramatic and idiosyncratic. As UV-B dosage increased, L. alba plants were less likely to flower, but suffered no delays in flowering or reductions to lifetime flower production for those that did flower. Conversely, an equal proportion of P. campanularia plants flowered under all UV-B treatments, but these same plants experienced delayed onset to bloom and produced fewer flowers at greater UV-B intensities. Therefore, intensified UV-B elicits idiosyncratic responses in flowering phenology and flower production from these two annual plants. Diurnal patterns in nectar and pollen production strongly coincided with fluctuating humidity and only weakly with UV-B dosage. Overall, our results indicated that intensified UV-B can alter some flowering traits that impinge upon plant competition for pollinator services, as well as plant and pollinator reproductive success.     

Flowering time and transcriptome variation in Capsella bursa-pastoris (Brassicaceae)

? Flowering is a major developmental transition and its timing in relation to environmental conditions is of crucial importance to plant fitness. Understanding the genetic basis of flowering time variation is important to determining how plants adapt locally. ? Here, we investigated flowering time variation of Capsella bursa-pastoris collected from different latitudes in China. We also used a digital gene expression (DGE) system to generate partial gene expression profiles for 12 selected samples. ? We found that flowering time was highly variable and most strongly correlated with day length and winter temperature. Significant differences in gene expression between early- and late-flowering samples were detected for 72 candidate genes for flowering time. Genes related to circadian rhythms were significantly overrepresented among the differentially expressed genes. ? Our data suggest that circadian rhythms and circadian clock genes play an important role in the evolution of flowering time, and C. bursa-pastoris plants exhibit expression differences for candidate genes likely to affect flowering time across the broad range of environments they face in China.     

Pre-dispersal seed predation in gynodioecious Geranium sylvaticum is not affected by plant gender or flowering phenology

Sex-specific interactions with antagonists may explain female maintenance in gynodioecious populations if seeds produced by hermaphroditic plants are preferred over seeds produced by female plants. Among antagonistic interactions, pre-dispersal seed predators have received relatively little attention even though they may exert sex-specific selective pressures on the evolution of floral and flowering traits. In this work, I investigate temporal variation in seed predation in gynodioecious Geranium sylvaticum, where in addition to female and hermaphrodite individuals, plants with an intermediate sexual expression are also present in most populations. Specifically, I examined whether seed predation is linked to flowering phenology, plant gender, and sexual dimorphism in floral and seed traits over the flowering season using an experimental field population. Within the population, I selected female, intermediate, and hermaphrodite plants with different timing of flowering onset (early, mid, or late), and collected seeds across the fruiting period. Seeds were weighed and examined for seed predator damage. The results show that the three genders experienced similar levels of seed predation attack regardless of their flowering phenology, and that overall seed predation was not related to changes in seed production or seed mass. These results suggest that sexual dimorphism in seed predation cannot be responsible for female maintenance in this species.