Floral trait differentiation in Anacamptis coriophora: Phenotypic selection on scents,but not on colour

Current divergent selection may promote floral trait differentiation among conspecific populations in flowering plants. However, whether this applies to complex traits such as colour or scents has been little studied, even though these traits often vary within species. In this study, we compared floral colour and odour as well as selective pressures imposed upon these traits among seven populations belonging to three subspecies of the widespread, generalist orchid Anacamptis coriophora. Colour was characterized using calibrated photographs, and scents were sampled using dynamic headspace extraction and analysed using gas chromatography–mass spectrometry. We then quantified phenotypic selection exerted on these traits by regressing fruit set values on floral trait values. We showed that the three studied subspecies were characterized by different floral colour and odour, with one of the two predominant floral volatiles emitted by each subspecies being taxon‐specific. Plant size was positively correlated with fruit set in most populations, whereas we found no apparent link between floral colour and female reproductive success. We detected positive selection on several taxon‐specific compounds in A. coriophora subsp. fragrans, whereas no selection was found on floral volatiles of A. coriophora subsp. coriophora and A. coriophora subsp. martrinii. This study is one of the first to document variation in phenotypic selection exerted on floral scents among conspecific populations. Our results suggest that selection could contribute to ongoing chemical divergence among A. coriophora subspecies.     

Day–night fluctuations in floral scent and their effects on reproductive success in <Emphasis Type="Italic">Lilium auratum</Emphasis>

We examined the contribution of diurnal and nocturnal pollination to male and female reproductive success in Lilium auratum. Plants were bagged for either 12 h during the day or at night to allow either only nocturnal or only diurnal visitors to forage throughout the flowering period. We found that there was no significant difference in the seed:ovule ratio among diurnally pollinated, nocturnally pollinated, or control flowers. However, in terms of male reproductive success, it was more advantageous for the plants to be pollinated both diurnally and nocturnally: the numbers of pollen grains remaining in diurnally pollinated or nocturnally pollinated flowers were significantly greater than those in control flowers. The total amount of floral volatiles of L. auratum was significantly higher at night than during the day. The constituents of floral scent of all time series examined were mostly monoterpenoids, many of which serve as attractants for nocturnal hawkmoths. Such nocturnally biased floral scent emission of L. auratum might achieve male reproductive success by attracting nocturnal visitors, which may suggest that the relative contribution of floral scent in this species is biased towards male reproductive success.     

Floral biology and reproductive isolation by floral scent in three sympatric aroid species in French Guiana

We studied the reproductive biology of three sympatric Araceae species, Anthurium sagittatum, A. thrinax and Spathiphyllum humboldtii in French Guiana. The plants flowered simultaneously and were visited by scent‐collecting male euglossine bees, which were apparently their major pollinators. In total, each species was visited by 3–7 euglossine species, and 2–3 euglossine species accounted for at least 80% of all flower visits, with visits being plant species‐specific. Floral scent consisted of 6–10 main compounds, which made up 76–94% of the total amount of volatiles and were specific in these high amounts to each plant species. We suggest that the different floral scents lead to clear separation of the main pollinating euglossine species, providing a directed and efficient intraspecific pollen flow that results in high reproductive success. Since the simple floral (inflorescence) morphology of the studied plants does not support any morphological mechanisms to exclude visitors, as for example in euglossine‐pollinated perfume orchids, floral scent might be of major importance for the reproductive isolation and sympatric occurrence of these plants.     

Trends in floral scent chemistry in pollination syndromes: floral scent composition in moth-pollinated taxa

KNUDSEN, J. T. & TOLLSTEN, L., Trends in floral scent chemistry in pollination syndromes: floral scent composition in moth-pollinated taxa. Floral scent from 15 moth-pollinated species in nine families was collected by head-space adsorption. The chemical composition was determined by coupled gas chromatography-mass spectrometry (GC-MS). The typical floral scent of moth-pollinated flowers contains some acyclic terpene alcohols, their corresponding hydrocarbons, benzenoid alcohols and esters and small amounts of some nitrogen compounds. The floral scent composition of sphingophilous flowers can be distinguished from that of phalaenophilous flowers by the presence of oxygenated sesquiterpenes. The flowers of three of the studied species had the general appearance and floral scent composition of moth-pollinated flowers, but contained no nectar reward. These species probably rely on deceptive pollination by naive visitors, which are deceived by the similarity of the flowers' morphological and scent chemistry to that of rewarding moth flowers. The finding of similar or structurally closely related floral scent compounds in both temperate and tropical species from both the Old and New worlds suggests that floral scent composition has been selected by a specific group of pollinators, moths that have similar sensory preferences. The functions of floral scent in moth-pollinated flowers are discussed in relation to an often observed over-representation of male moth visitors.     

Three diurnal patterns of anthesis in Ipomoea carnea subsp. fistulosa (Convolvulaceae): Implications for temporal,behavioral and morphological characteristics of pollinators?

Flowers of Ipomoea are characterized mainly by being ephemeral and showy. They attract many floral visitors of different taxonomic groups, whose activity is generally synchronized with opening and closing times of flowers. In this study we tested whether flowering, morphology and floral biology of Ipomoea carnea subsp. fistulosa were related to pollinator dynamics and environmental factors, emphasizing temporal and behavioral aspects in different months of the year, in an area shaped by human activities of the semi-arid region of Bahia, northeastern Brazil. Observations were made for three days each month, from October 2009 to August 2010 in the campus of the State University of Feira de Santana. We investigated morphology, floral biology, reproductive system, and flowering of I. carnea, and collected floral visitors. Flowering occurred in all months. Flowers opened during three periods of the day: morning, afternoon and night, with life-time of the respective flowers being 11, 19, and 16 h in each period, respectively. The study species is self-incompatible. Flowers were visited predominantly by bees and moths, and exhibit morphological traits related to the syndromes of melittophily and phalaenophily. The conspicuous pink flowers attracted bees and the strong sweet scent produced during the night attracted moths. The bees Apis mellifera, Melitomella murihirta, Melitoma aff. segmentaria and Pseudaugochlora pandora were considered as potential diurnal pollinators, and the hawkmoth Agrius cingulata as a potential nocturnal pollinator. The 24 h flower display increases the chance of pollination, especially for ruderal and weedy species such as I. carnea subsp. fistulosa^© 2013 Elsevier GmbH.     

Divergent selection on flowering phenology but not on floral morphology between two closely related orchids

Closely related species often differ in traits that influence reproductive success, suggesting that divergent selection on such traits contribute to the maintenance of species boundaries. Gymnadenia conopsea ss. and Gymnadenia densiflora are two closely related, perennial orchid species that differ in (a) floral traits important for pollination, including flowering phenology, floral display, and spur length, and (b) dominant pollinators. If plant–pollinator interactions contribute to the maintenance of trait differences between these two taxa, we expect current divergent selection on flowering phenology and floral morphology between the two species. We quantified phenotypic selection via female fitness in one year on flowering start, three floral display traits (plant height, number of flowers, and corolla size) and spur length, in six populations of G. conopsea s.s. and in four populations of G. densiflora. There was indication of divergent selection on flowering start in the expected direction, with selection for earlier flowering in two populations of the early‐flowering G. conopsea s.s. and for later flowering in one population of the late‐flowering G. densiflora. No divergent selection on floral morphology was detected, and there was no significant stabilizing selection on any trait in the two species. The results suggest ongoing adaptive differentiation of flowering phenology, strengthening this premating reproductive barrier between the two species. Synthesis: This study is among the first to test whether divergent selection on floral traits contribute to the maintenance of species differences between closely related plants. Phenological isolation confers a substantial potential for reproductive isolation, and divergent selection on flowering time can thus greatly influence reproductive isolation and adaptive differentiation.     

Phenotypic selection to increase floral scent emission, but not flower size or colour in bee-pollinated Penstemon digitalis

Fragrance is a putatively important character in the evolution of flowering plants, but natural selection on scent is rarely studied and thus poorly understood. We characterized floral scent composition and emission in a common garden of Penstemon digitalis from three nearby source populations. We measured phenotypic selection on scent as well as floral traits more frequently examined, such as floral phenology, display size, corolla pigment, and inflorescence height. Scent differed among populations in a common garden, underscoring the potential for scent to be shaped by differential selection pressures. Phenotypic selection on flower number and display size was strong. However, selection favoured scent rather than flower size or colour, suggesting that smelling stronger benefits reproductive success in P. digitalis. Linalool was a direct target of selection and its high frequency in floral-scent bouquets suggests that further studies of both pollinator- and antagonist-mediated selection on this compound would further our understanding of scent evolution. Our results indicate that chemical dimensions of floral display are just as likely as other components to experience selective pressure in a nonspecialized flowering herb. Therefore, studies that integrate visual and chemical floral traits should better reflect the true nature of floral evolutionary ecology.     

Why Do Floral Perfumes Become Different? Region-Specific Selection on Floral Scent in a Terrestrial Orchid

Geographically structured phenotypic selection can lead to adaptive divergence. However, in flowering plants, such divergent selection has rarely been shown, and selection on floral signals is generally little understood. In this study, we measured phenotypic selection on display size, floral color, and floral scent in four lowland and four mountain populations of the nectar-rewarding terrestrial orchid Gymnadenia odoratissima in two years. We also quantified population differences in these traits and pollinator community composition. Our results show positive selection on display size and positive, negative, or absence of selection on different scent compounds and floral color. Selection on the main scent compounds was consistently stronger in the lowlands than in the mountains, and lowland plants emitted higher amounts of most of these compounds. Pollinator community composition also differed between regions, suggesting different pollinators select for differences in floral volatiles. Overall, our study is the first to document consistent regional differences in selection on floral scent, suggesting this pattern of selection is one of the evolutionary forces contributing to regional divergence in floral chemical signaling.     

PLANT POLYPLOIDY AND POLLINATION: FLORAL TRAITS AND INSECT VISITS TO DIPLOID AND TETRAPLOID HEUCHERA GROSSULARIIFOLIA

In many polyploid species, polyploids often have different suites of floral traits and different flowering times than their diploid progenitor species. We hypothesized that such differences in floral traits in polyploids may subsequently affect their interactions with pollinating and other insect visitors. We measured floral morphology and flowering phenology in 14 populations of diploid and autotetraploid Heuchera grossulariifolia Rydb. (Saxifragaceae), determined if repeated evolution of independent polyploid lineages resulted in differentiation in floral morphology among those lineages, and ascertained if there was a consistent pattern of differentiation among genetically similar diploid and autotetraploid populations. In addition, we evaluated the differences in suites of floral visitors within a natural community where diploids and autotetraploids occur sympatrically. Overall, flowers of autotetraploid plants were larger and shaped differently than those of diploids, had a different flowering phenology than that of diploids, and attracted different suites of floral visitors. In comparison with flowers of diploids, tetraploid floral morphology varied widely from pronounced differences between cytotypes in some populations to similar flower shapes and sizes between ploidal levels in other populations. Observations of floral visitors to diploids and autotetraploids in a natural sympatric population demonstrated that the cytotypes had different suites of floral visitors and six of the 15 common visitors preferentially visited one ploidy more frequently. Moreover, we also found that floral morphology differed among independent autotetraploid origins, but there was no consistent pattern of differentiation between genetically similar diploid and autotetraploid populations. Hence, the results suggest that the process of polyploidization creates the potential for attraction of different suites of floral visitors. Multiple origins of polyploidy also presents the opportunity for new or different plant-insect interactions among independent polyploid lineages. These differences in turn may affect patterns of gene flow between diploids and polyploids and also among plants of independent polyploid origin. Polyploidy, therefore, may result in a geographic mosaic of interspecific interactions across a species' range, contributing to diversification in both plant and insect groups.     

Sexual and temporal variations in floral scent in the subdioecious shrub Eurya japonica Thunb

In many flowering plants, floral scents are a significant trait for visitors, playing an important role in attracting pollinators and/or detracting herbivores. The evolution of flowering plants from hermaphroditism to dioecy is often accompanied by sexual dimorphism in floral scent. In this study, floral scents emitted by different sexual morphs of the subdioecious shrub Eurya japonica Thunb. were collected using a dynamic headspace method, and sexual and temporal variations were evaluated by gas chromatography–mass spectrometry (GC–MS). Two volatiles, α‐pinene and linalool, were identified as the major components of floral scents in females, hermaphrodites, and males. The males emit higher amounts of floral scents, particularly α‐pinene, compared to females or hermaphrodites. Floral scents emitted by males generally decrease as flowers enter senescence, whereas those from females or hermaphrodites do not significantly differ. Intraspecific variations in floral scents of subdioecious species provided by this study would contribute to better understanding of sexual dimorphism in floral scent.     

HUA2 caused natural variation in shoot morphology of A. thaliana

Differences in life-history strategy are thought to contribute to adaptation to specific environmental conditions. Among life-history traits in plants, flowering time and shoot morphology are particularly important for reproductive success. Even though flowering time and shoot morphology are linked, the evolutionary changes in the genetic circuitry that simultaneously affects both traits remain obscure. Here, we have identified changes in a putative pre-mRNA processing factor, HUA2, as being responsible for the distinct shoot morphology and flowering behavior in Sy-0, a natural strain of Arabidopsis. HUA2 has previously been shown to positively regulate two MADS box genes affecting flowering time (FLOWERING LOCUS C [FLC]) and floral patterning (AGAMOUS [AG]) [1, 2]. We demonstrate that natural changes in HUA2 activity have opposite effects on its known functions, thus having implications for the coordinate control of induction and maintenance of floral fate. The changes in Sy-0 lead to enhanced FLC expression, resulting in an enlarged basal rosette and aerial rosettes, whereas suppression of AG function favors a reversion of floral meristems from determinate to indeterminate development. Natural variation in HUA2 activity thus coordinates changes in two important life-history traits, flowering time and shoot morphology.     

Evolutionary breakdown of distyly to homostyly is accompanied by reductions of floral scent in Primula oreodoxa

Reproductive traits that function in pollinator attraction may be reduced or lost during evolutionary transitions from outcrossing to selfing. Although floral scent plays an important role in attracting pollinators in outcrossing species, few studies have investigated associations between floral scent variation and intraspecific mating system transitions. The breakdown of distyly to homostyly represents a classic example of a shift from outcrossing to selfing and provides an opportunity to test whether floral fragrances have become reduced and/or changed in composition with increased selfing. Here, we evaluate this hypothesis by quantifying floral volatiles using gas chromatography-mass spectrometry in two distylous and four homostylous populations of Primula oreodoxa Franchet, a perennial herb from SW China. Our analysis revealed significant variation of volatile organic compounds (VOCs) among populations of P. oreodoxa. Although there was no difference in VOCs between floral morphs in distylous populations as predicted, we detected a substantial reduction in VOC emissions and the average number of scent compounds in homostylous compared with distylous populations. A total of 12 compounds, mainly monoterpenoids and sesquiterpenoids, distinguished homostylous and distylous morphs; of these, (E)-β-ocimene was the most important in contributing to the difference in volatiles, with significantly lower emissions in homostyles. Our findings support the hypothesis that the transition from outcrossing to selfing is accompanied by the loss of floral volatiles. The modification to floral fragrances in P. oreodoxa associated with mating system change might occur because high selfing rates in homostylous populations result in relaxed selection for floral attractiveness.     

Reproductive isolation of two sympatric subspecies ofJuniperus phoenicea (Cupressaceae) in southern Spain

The phenology, reproductive cycle and cone crop of two sympatric subspecies ofJuniperus phoenicea (Cupressaceae) were studied during three consecutive years in southern Spain. The flowering pattern of each subspecies was constant during this period: inJ. phoenicea subsp.turbinata flowering was always in October–November, whileJ. phoenicea subsp.phoenicea flowered in February–March. There was no overlap between the flowering periods of the two taxa. The reproductive cycle of the two subspecies was similar, though there were some important differences because of their flowering times. Male cone development in both subspecies occurred in autumn, but the male cones ofJ. phoenicea subsp.phoenicea did not shed pollen until the end of February. InJ. phoenicea subsp.turbinata, the gap between pollination and fertilisation was seven months while inJ. phoenicea subsp.phoenicea it was only three months, fertilisation taking place at the same time in the two taxa. Post-fertilisation events were similar in the two subspecies, leading to a cycle of two years inJ. phoenicea subsp.turbinata and a shorter one of about 20 months inJ. phoenicea subsp.phoenicea. Alternating good and slight seed cone crops were found in both taxa during the three years studied, the good crops of one subspecies coinciding with the slight crops of the other one. Although the proximity of the two subspecies and method of pollination could make hybridisation between the taxa possible, the different flowering seasons prevent hybridisation isolating them reproductively.     

The generalist Inga subnuda subsp. luschnathiana (Fabaceae): negative effect of floral visitors on reproductive success?

Inga species are characterised by generalist or mixed pollination system. However, this feature does not enhance reproductive rates in species with very low fruit set under natural conditions. Some ecological and genetic factors are associated with this feature, and to test the effect of massive visits on pollination success in Inga subnuda subsp. luschnathiana, we studied the efficacy of polyads deposited on stigmas of flowers isolated from visitors and polyads exposed to visitors. The proportion of polyads fixed in stigmas decreased after exposure to visitors (24 h) in comparison to stigmas isolated from visitors (hummingbirds, bees, wasps, hawkmoths and bats), and fruit set was very low. Furthermore, nectar production, sugar composition and other floral biology traits were evaluated. Increased nectar production, sugar availability and sucrose dominance during the night indicates adaptation to nocturnal visitors and supports their role as main pollinators; although the brush‐flower morphology, time of anthesis, nectar dynamics and chemical composition also allow daytime visitors. Thus the species is an important resource for a diverse group of floral visitors. We conclude that excess visits (diurnal and nocturnal) are responsible for the decrease in fixed polyads in stigmas of I. subnuda subsp. luschnathiana flowers, thus contributing, with others factors, to its low fruit set. Therefore, the generalist pollination system does not result in reproductive advantages because the low fruit set in natural conditions could be the result of a negative effect of visitors/pollinators.     

The genetic architecture of natural variation in flower morphology

A pollination syndrome is defined as a suite of floral traits that are associated with the attraction of a specific group of animals as pollinators. Traits such as flower morphology, color, scent, and rewards contribute to the plant's reproductive success by attracting pollinators. Here we focus on the genetics of natural variation in flower morphology and how the adaptation between plants and their cognate pollinator class contributes to plant's reproductive success. We review recent work on the genetic basis of interspecific differences in reproductive organ morphology and discuss possible genetic mechanisms for coordinated changes in complex syndromes.     

Evolution and diversity of floral scent chemistry in the euglossine bee-pollinated orchid genus Gongora

•Background and Aims Animal-pollinated angiosperms have evolved a variety of signalling mechanisms to attract pollinators. Floral scent is a key component of pollinator attraction, and its chemistry modulates both pollinator behaviour and the formation of plant–pollinator networks. The neotropical orchid genus Gongora exhibits specialized pollinator associations with male orchid bees (Euglossini). Male bees visit orchid flowers to collect volatile chemical compounds that they store in hind-leg pouches to use subsequently during courtship display. Hence, Gongora floral scent compounds simultaneously serve as signalling molecules and pollinator rewards. Furthermore, because floral scent acts as the predominant reproductive isolating barrier among lineages, it has been hypothesized that chemical traits are highly species specific. A comparative analysis of intra- and inter-specific variation of floral scent chemistry was conducted to investigate the evolutionary patterns across the genus.•Methods Gas chromatography–mass spectrometry (GC-MS) was used to analyse the floral scent of 78 individuals belonging to 28 different species of Gongora from two of the three major lineages sampled across the neotropical region. Multidimensional scaling and indicator value analyses were implemented to investigate the patterns of chemical diversity within and among taxonomic groups at various geographic scales. Additionally, pollinator observations were conducted on a sympatric community of Gongora orchids exhibiting distinct floral scent phenotypes.•Key Results A total of 83 floral volatiles, mainly terpenes and aromatic compounds, were detected. Many of the identified compounds are common across diverse angiosperm families (e.g. cineole, eugenol, β-ocimene, β-pinene and terpinen-4-ol), while others are relatively rare outside euglossine bee-pollinated orchid lineages. Additionally, 29 volatiles were identified that are known to attract and elicit collection behaviour in male bees. Floral scent traits were less variable within species than between species, and the analysis revealed exceptional levels of cryptic diversity. Gongora species were divided into 15 fragrance groups based on shared compounds. Fragrance groups indicate that floral scent variation is not predicted by taxonomic rank or biogeographic region.•Conclusions Gongora orchids emit a diverse array of scent molecules that are largely species specific, and closely related taxa exhibit qualitatively and quantitatively divergent chemical profiles. It is shown that within a community, Gongora scent chemotypes are correlated with near non-overlapping bee pollinator assemblies. The results lend support to the hypothesis that floral scent traits regulate the architecture of bee pollinator associations. Thus, Gongora provides unique opportunities to examine the interplay between floral traits and pollinator specialization in plant–pollinator mutualisms.     

Floral adaptation to local pollinator guilds in a terrestrial orchid

Background and Aims

Studies of local floral adaptation in response to geographically divergent pollinators are essential for understanding floral evolution. This study investigated local pollinator adaptation and variation in floral traits in the rewarding orchid Gymnadenia odoratissima, which spans a large altitudinal gradient and thus may depend on different pollinator guilds along this gradient.

Methods

Pollinator communities were assessed and reciprocal transfer experiments were performed between lowland and mountain populations. Differences in floral traits were characterized by measuring floral morphology traits, scent composition, colour and nectar sugar content in lowland and mountain populations.

Key Results

The composition of pollinator communities differed considerably between lowland and mountain populations; flies were only found as pollinators in mountain populations. The reciprocal transfer experiments showed that when lowland plants were transferred to mountain habitats, their reproductive success did not change significantly. However, when mountain plants were moved to the lowlands, their reproductive success decreased significantly. Transfers between populations of the same altitude did not lead to significant changes in reproductive success, disproving the potential for population-specific adaptations. Flower size of lowland plants was greater than for mountain flowers. Lowland plants also had significantly higher relative amounts of aromatic floral volatiles, while the mountain plants had higher relative amounts of other floral volatiles. The floral colour of mountain flowers was significantly lighter compared with the lowland flowers.

Conclusions

Local pollinator adaptation through pollinator attraction was shown in the mountain populations, possibly due to adaptation to pollinating flies. The mountain plants were also observed to receive pollination from a greater diversity of pollinators than the lowland plants. The different floral phenotypes of the altitudinal regions are likely to be the consequence of adaptations to local pollinator guilds.     

POLLINATOR-MEDIATED SELECTION ON FLORAL DISPLAY AND FLOWERING TIME IN THE PERENNIAL HERB ARABIDOPSIS LYRATA

The evolution of floral display and flowering time in animal-pollinated plants is commonly attributed to pollinator-mediated selection. Yet, the causes of selection on flowering phenology and traits contributing to floral display have rarely been tested experimentally in natural populations. We quantified phenotypic selection on morphological and phenological characters in the perennial, outcrossing herb Arabidopsis lyrata in two years using female reproductive success as a proxy of fitness. To determine whether selection on floral display and flowering phenology can be attributed to interactions with pollinators, selection was quantified both for open-pollinated controls and for plants receiving supplemental hand-pollination. We documented directional selection for many flowers, large petals, late start of flowering, and early end of flowering. Seed output was pollen-limited in both years and supplemental hand-pollination reduced the magnitude of selection on number of flowers, and reversed the direction of selection on end of flowering. The results demonstrate that interactions with pollinators may affect the strength of selection on floral display and the direction of selection on phenology of flowering in natural plant populations. They thus support the contention that pollinators can drive the evolution of both floral display and flowering time.     

Floral scent emission is the highest at the second night of anthesis in Lonicera japonica (Caprifoliaceae)

Floral color change in diverse plants has been thought to be a visual signal reflecting changes in floral rewards, promoting pollinator foraging efficiency as well as plant reproductive success. It remains unclear whether olfactory signals co-vary with floral color change. We investigated the production rhythms of floral scent and nectar associated with floral color change in Lonicera japonica. The flowers generally last 2–3 days. They are white on opening at night (N1) and become light yellow the following day (D1), yellow on the second night (N2), and golden on the second day of flowering (D2). Our measurements in the four stages indicated that nectar production decreased significantly from N1 and D1 to N2 and D2, tracking the floral color change. A total of 34 compounds were detected in floral scent and total scent emission was significantly higher in N2 than in the other three stages. The scent emission of three major compounds, Linalool, cis-3-Hexenyl tiglate, and Germacrene D was also significantly higher in N2, but the relative content of Linalool decreased gradually, cis-3-Hexenyl tiglate increased gradually, and the relative content of Germacrene D did not differ among the four measured stages. Greater scent emission by night than by day suggested a strong olfactory signal to attract nocturnal hawkmoths, the effective pollinators. However, floral scent rhythms in the four stages did not match the color change and nectar secretion, suggesting that floral color (visual) and scent (olfactory) in this species may play different roles in attracting or filtering various visitors.     

Herbivore‐induced changes in flower scent and morphology affect the structure of flower–visitor networks but not plant reproduction

Herbivory induces various responses in plants, thus altering the plants’ phenotype in chemical and morphological traits. Herbivore‐induced changes in vegetative plant parts, plant‐physiological mechanisms, and effects on plant‐animal interactions have been intensively studied from species to community level. In contrast, we are just beginning to examine herbivore‐induced effects on reproductive plant parts and flower–visitor interactions, especially in a community context. We investigated the effect of herbivory at different plant developmental stages on plant growth, floral and vegetative phenotype and reproduction in Sinapis arvensis (Brassicaceae). Additionally, we tested how herbivore‐induced plant responses affect flower–visitor interactions and plant reproduction in species‐rich communities. Our results indicate that the timing of herbivory affects the magnitude of changes in plant traits. Herbivory in early but not in late development accelerated the plant's flowering phenology, reduced vegetative growth, increased stem trichome density and altered floral morphology and scent. These findings suggest age‐dependent tradeoffs between growth, defense and reproduction. Herbivore‐induced changes in flower traits also affected flower–visitor interactions in a community context with effects on the structure of flower–visitor networks. However, changes in the network structure had neglectable effects on plant reproduction, i.e. plants were able to compensate altered flower visitor behavior. Thus, herbivory is a source of intraspecific variation in reproductive traits, which can be behaviorally relevant for potential pollinators. However, plants were capable to maintain reproductive success suggesting a tolerance against herbivory. We conclude that in our study system induced direct or indirect defenses that have often been shown to decrease negative effects of herbivores on vegetative plant parts come at no costs for plant reproduction.