小果叶下珠花气味组成及其两性异型性

大戟科(Euphorbiaceae)植物小果叶下珠(Phyllanthus microcarpus)由种特异性细蛾科(Gracillariidae)昆虫头细蛾(Epicephala)专门为其传粉,具体包括:头细蛾在雄花上积极采粉,然后为雌花授粉并在其内产卵等极其不同的传粉行为。花气味在维持小果叶下珠与传粉头细蛾专性传粉互利共生关系中起着至关重要的作用。采用动态顶空吸附法分别收集小果叶下珠雌花和雄花气味,利用气相色谱-质谱(gas chromatography-mass spectrometry,GC-MS)联用技术分析鉴定其成分,并用峰面积归一法与内标法进行定量,最后通过主成分分析法比较两者间的差异性。结果表明:(1)小果叶下珠花气味中共分离出17种化合物,主要以萜类和脂肪族物质为主;顺-β-罗勒烯在雌花和雄花中含量均最高,为主要气味成分;(2)雌花气味释放量显著高于雄花;(3)雌花和雄花之间气味化学成分存在明显的差异,即具有两性异形性。初步推测花气味出现两性异形性是植物为适应传粉头细蛾极其高度特异的传粉行为(雄花采粉,雌花传粉并产卵)而选择进化的结果。     

黑面神雌花气味传粉前后的变化及其生态意义

该文以与头细蛾传粉相关的叶下珠科植物黑面神为材料,采用动态顶空吸附法分别收集了该物种雌花传粉前后释放的挥发物,利用气相色谱-质谱联用技术分析了其化学成分,探索了三者间花气味的异同,并对其生态意义进行了讨论。结果表明:从该物种传粉前、传粉期和传粉后的雌花气味中共分离出22种挥发物(传粉前12种,传粉期15种和传粉后13种),以脂肪族衍生物和萜类物质为主。3-己烯醛、反-2-己烯醛、顺-3-己烯-1-醇、顺-乙酸-3-己烯酯、反-β-罗勒烯、β-石竹烯、β-蛇麻烯、反,反-α-金合欢烯和长叶烯是其主要挥发物。传粉前后雌花气味的化学种类及组成发生了显著分化,且这种变化主要是由于各时期主要挥发物发生改变而引起的。反-β-罗勒烯在传粉期含量最高,而在传粉后显著下降,3-己烯、反-2-己烯醛、顺-3-己烯-1-醇和顺-乙酸-3-己烯酯在传粉前含量均最高,β-石竹烯含量在传粉后显著升高,且长叶烯仅在传粉后出现。在传粉期和传粉后β-蛇麻烯和反,反-α-金合欢烯的含量均显著上升。同时,传粉期雌花的释放量明显高于传粉前和传粉后的。综上结果显示,黑面神雌花传粉前后花气味发生了质与量的改变。初步推测黑面神雌花...     

Assessment of the diversity and species specificity of the mutualistic association between Epicephala moths and Glochidion trees

The obligate mutualisms between flowering plants and their seed-parasitic pollinators constitute fascinating examples of interspecific mutualisms, which are often characterized by high levels of species diversity and reciprocal species specificity. The diversification in these mutualisms has been thought to occur through simultaneous speciation of the partners, mediated by tight reciprocal adaptation; however, recent studies cast doubt over this general view. In this study, we examine the diversity and species specificity of Epicephala moths (Gracillariidae) that pollinate Glochidion trees (Phyllanthaceae), using analysis of mitochondrial and nuclear gene sequences. Phylogenetic analysis of Epicephala moths associated with five Glochidion species in Japan and Taiwan reveal six genetically isolated species that are also distinguishable by male genital morphology: (i) two species specific to single host species (G. acuminatum and G. zeylanicum, respectively); (ii) two species that coexist on G. lanceolatum; and (iii) two species that share two, closely-related parapatric hosts (G. obovatum and G. rubrum). Statistical analysis shows that the two species associated with G. lanceolatum are not sister species, indicating the colonization of novel Glochidion host in at least one lineage. Behavioural observations suggest that all six species possess the actively-pollinating habit, thus none of the studied species has become a nonmutualistic 'cheater' that exploits the benefit resulting from pollination by other species. Our results parallel recent findings in ecologically similar associations, namely the fig-fig wasp and yucca-yucca moth mutualisms, and contribute to a more general understanding of the factors that determine ecological and evolutionary outcomes in these mutualisms.     

Repeated colonization of remote islands by specialized mutualists

Mutualisms are ubiquitous in nature, but constraints imposed by specialization may limit their ability to colonize novel environments synchronously. The ability of mutualisms to reassemble following disturbance is central to understanding their response to global change. Here, we demonstrate that a highly specialized pollination mutualism considered to be obligate (Phyllanthaceae: Glochidion; Lepidoptera: Gracillariidae: Epicephala) has colonized some of the world's most isolated archipelagoes, and we record, to our knowledge, for the first time the presence of Epicephala moths from 19 host Glochidion species on 17 islands in the Pacific Ocean. Our findings appear to offer a remarkable example of mutualism persistence in an insect-plant interaction characterized by reciprocal specialization and mutual dependence. These findings also appear to contradict the island biogeography paradigm that taxa with specialized biotic interactions are unlikely to colonize oceanic islands.     

Natural selection on floral volatile production in Penstemon digitalis: Highlighting the role of linalool

Natural selection is thought to have shaped the evolution of floral scent; however, unlike other floral characters, we have a rudimentary knowledge of how phenotypic selection acts on scent. We found that floral scent was under stronger selection than corolla traits such as flower size and flower color in weakly scented Penstemon digitalis. Our results suggest that to understand evolution in floral phenotypes, including scent in floral selection, studies are crucial. For P. digitalis, linalool was the direct target of selection in the scent bouquet. Therefore, we determined the enantiomeric configuration of linalool because interacting insects may perceive the enantiomers differentially. We found that P. digitalis produces only (S)-(+)-linalool and, more interestingly, it is also taken up into the nectar. Because the nectar is scented and flavored with (S)-(+)-linalool, it may be an important cue for pollinators visiting P. digitalis flowers.     

Morphological and physiological divergences within Quercus ilex support the existence of different ecotypes depending on climatic dryness

Background and Aims

According to the Grant–Stebbins model of pollinator-driven divergence, plants that disperse beyond the range of their specialized pollinator may adapt to a new pollination system. Although this model provides a compelling explanation for pollination ecotype formation, few studies have directly tested its validity in nature. Here we investigate the distribution and pollination biology of several subspecies of the shrub Erica plukenetii from the Cape Floristic Region in South Africa. We analyse these data in a phylogenetic context and combine these results with information on pollinator ranges to test whether the evolution of pollination ecotypes is consistent with the Grant–Stebbins model.

Methods and Key Results

Pollinator observations showed that the most common form of E. plukenetii with intermediate corolla length is pollinated by short-billed Orange-breasted sunbirds. Populations at the northern fringe of the distribution are characterized by long corollas, and are mainly pollinated by long-billed Malachite sunbirds. A population with short corollas in the centre of the range was mainly pollinated by insects, particularly short-tongued noctuid moths. Bird exclusion in this population did not have an effect on fruit set, while insect exclusion reduced fruit set. An analysis of floral scent across the range, using coupled gas chromatography–mass spectrometry, showed that the scent bouquets of flowers from moth-pollinated populations are characterized by a larger number of scent compounds and higher emission rates than those in bird-pollinated populations. This was also reflected in clear separation of moth- and bird-pollinated populations in a two-dimensional phenotype space based on non-metric multidimensional scaling analysis of scent data. Phylogenetic analyses of chloroplast and nuclear DNA sequences strongly supported monophyly of E. plukenetii, but not of all the subspecies. Reconstruction of ancestral character states suggests two shifts from traits associated with short-billed Orange-breasted sunbird pollination: one towards traits associated with moth pollination, and one towards traits associated with pollination by long-billed Malachite sunbirds. The latter shift coincided with the colonization of Namaqualand in which Orange-breasted sunbirds are absent.

Conclusions Erica plukenetii

is characterized by three pollination ecotypes, but only the evolutionary transition from short- to long-billed sunbird pollination can be clearly explained by the Grant–Stebbins model. Corolla length is a key character for both ecotype transitions, while floral scent emission was important for the transition from bird to moth pollination.     

Why do so many petals have conical epidermal cells?

Background

The conical epidermal cells found on the petals of most Angiosperm species are so widespread that they have been used as markers of petal identity, but their function has only been analysed in recent years. This review brings together diverse data on the role of these cells in pollination biology.

Scope

The published effects of conical cells on petal colour, petal reflexing, scent production, petal wettability and pollinator grip on the flower surface are considered. Of these factors, pollinator grip has been shown to be of most significance in the well-studied Antirrhinum majus/bumble-bee system. Published data on the relationship between epidermal cell morphology and floral temperature were limited, so an analysis of the effects of cell shape on floral temperature in Antirrhinum is presented here. Statistically significant warming by conical cells was not detected, although insignificant trends towards faster warming at dawn were found, and it was also found that flat-celled flowers could be warmer on warm days. The warming observed is less significant than that achieved by varying pigment content. However, the possibility that the effect of conical cells on temperature might be biologically significant in certain specific instances such as marginal habitats or weather conditions cannot be ruled out.

Conclusions

Conical epidermal cells can influence a diverse set of petal properties. The fitness benefits they provide to plants are likely to vary with pollinator and habitat, and models are now required to understand how these different factors interact.     

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.     

Geographical matching of volatile signals and pollinator olfactory responses in a cycad brood-site mutualism

Brood-site mutualisms represent extreme levels of reciprocal specialization between plants and insect pollinators, raising questions about whether these mutualisms are mediated by volatile signals and whether these signals and insect responses to them covary geographically in a manner expected from coevolution. Cycads are an ancient plant lineage in which almost all extant species are pollinated through brood-site mutualisms with insects. We investigated whether volatile emissions and insect olfactory responses are matched across the distribution range of the African cycad Encephalartos villosus. This cycad species is pollinated by the same beetle species across its distribution, but cone volatile emissions are dominated by alkenes in northern populations, and by monoterpenes and a pyrazine compound in southern populations. In reciprocal choice experiments, insects chose the scent of cones from the local region over that of cones from the other region. Antennae of beetles from northern populations responded mainly to alkenes, while those of beetles from southern populations responded mainly to pyrazine. In bioassay experiments, beetles were most strongly attracted to alkenes in northern populations and to the pyrazine compound in southern populations. Geographical matching of cone volatiles and pollinator olfactory preference is consistent with coevolution in this specialized mutualism.     

On the roles of colour and scent in a specialized floral mimicry system

Background and Aims

Sexually deceptive orchids achieve cross-pollination by mimicking the mating signals of female insects, generally hymenopterans. This pollination mechanism is often highly specific as it is based primarily on the mimicry of mating signals, especially the female sex pheromones of the targeted pollinator. Like many deceptive orchids, the Mediterranean species Ophrys arachnitiformis shows high levels of floral trait variation, especially in the colour of the perianth, which is either green or white/pinkinsh within populations. The adaptive significance of perianth colour polymorphism and its influence on pollinator visitation rates in sexually deceptive orchids remain obscure.

Methods

The relative importance of floral scent versus perianth colour in pollinator attraction in this orchid pollinator mimicry system was evaluated by performing floral scent analyses by gas chromatography-mass spectrometry (GC-MS) and behavioural bioassays with the pollinators under natural conditions were performed.

Key Results

The relative and absolute amounts of behaviourally active compounds are identical in the two colour morphs of O. arachnitiformis. Neither presence/absence nor the colour of the perianth (green versus white) influence attractiveness of the flowers to Colletes cunicularius males, the main pollinator of O. arachnitiformis.

Conclusion

Chemical signals alone can mediate the interactions in highly specialized mimicry systems. Floral colour polymorphism in O. arachnitiformis is not subjected to selection imposed by C. cunicularius males, and an interplay between different non-adaptive processes may be responsible for the maintenance of floral colour polymorphism both within and among populations.     

Floral closure induced by pollination in gynodioecious Cyananthus delavayi (Campanulaceae): effects of pollen load and type, floral morph and fitness consequences

Background and aims

Pollination-induced floral changes, which have been widely documented in flowering plants, have been assumed to enhance the plant''s reproductive success. However, our understanding of the causes and consequences of these changes is still limited. Using an alpine gynodioecious species, Cyananthus delavayi, we investigated the factors affecting floral closure and estimated the fitness consequences of floral closure.

Methods

The timings of floral closure and fertilization were determined. The effects of pollen load, pollen type (cross- or self-pollen) and floral morph (female or perfect flower) on the occurrence of floral closure were examined. Ovule fertilization and seed production were examined to investigate the causes and consequences of floral closure. Flowers were manipulated to prevent closing to detect potential benefits for female fitness.

Key Results

Floral closure, which could be induced by a very low pollen load, occurred within 4–7 h after pollination, immediately following fertilization. The proportion of closed flowers was influenced by pollen load and floral morph, but not by pollen type. Floral closure was more likely to occur in flowers with a higher proportion of fertilized ovules, but there was no significant difference in seed production between closed and open flowers. Those flowers in which closure was induced by natural pollination had low fruit set and seed production. Additionally, seed production was not influenced by closing-prevented manipulation when sufficient pollen deposition was received.

Conclusions

The occurrence of floral closure may be determined by the proportion of fertilized ovules, but this response can be too sensitive to ensure sufficient pollen deposition and can, to some extent, lead to a cost in female fitness. These results implied that the control of floral receptivity by the recipient flowers does not lead to an optimal fitness gain in C. delavayi.     

Hummingbird responses to gender-biased nectar production: are nectar biases maintained by natural or sexual selection?

Pollinators mediate the evolution of secondary floral traits through both natural and sexual selection. Gender-biased nectar, for example, could be maintained by one or both, depending on the interactions between plants and pollinators. Here, I investigate pollinator responses to gender-biased nectar using the dichogamous herb Chrysothemis friedrichsthaliana (Gesneriaceae) which produces more nectar during the male floral phase. Previous research showed that the hummingbird pollinator Phaethornis striigularis visited male-phase flowers more often than female-phase flowers, and multiple visits benefited male more than female fecundity. If sexual selection maintains male-biased rewards, hummingbirds should prefer more-rewarding flowers independent of floral gender. If, however, differential rewards are partially maintained through natural selection, hummingbirds should respond to asymmetry with visits that reduce geitonogamy, i.e. selfing and pollen discounting. In plants with male biases, these visit types include single-flower visits and movements from low to high rewards. To test these predictions, I manipulated nectar asymmetry between pairs of real or artificial flowers on plants and recorded foraging behaviour. I also assessed maternal costs of selfing using hand pollinations. For plants with real flowers, hummingbirds preferred more-rewarding flowers and male-phase morphology, the latter possibly owing to previous experience. At artificial arrays, hummingbirds responded to extreme reward asymmetry with increased single-flower visits; however, they moved from high to low rewards more often than low to high. Finally, selfed flowers did not produce inferior seeds. In summary, sexual selection, more so than geitonogamy avoidance, maintains nectar biases in C. friedrichsthaliana, in one of the clearest examples of sexual selection in plants, to date.     

Are tetraploids more successful? Floral signals,reproductive success and floral isolation in mixed-ploidy populations of a terrestrial orchid

Background and Aims Polyploidization, the doubling of chromosome sets, is common in angiosperms and has a range of evolutionary consequences. Newly formed polyploid lineages are reproductively isolated from their diploid progenitors due to triploid sterility, but also prone to extinction because compatible mating partners are rare. Models have suggested that assortative mating and increased reproductive fitness play a key role in the successful establishment and persistence of polyploids. However, little is known about these factors in natural mixed-ploidy populations. This study investigated floral traits that can affect pollinator attraction and efficiency, as well as reproductive success in diploid and tetraploid Gymnadenia conopsea (Orchidaceae) plants in two natural, mixed-ploidy populations.Methods Ploidy levels were determined using flow cytometry, and flowering phenology and herbivory were also assessed. Reproductive success was determined by counting fruits and viable seeds of marked plants. Pollinator-mediated floral isolation was measured using experimental arrays, with pollen flow tracked by means of staining pollinia with histological dye.Key Results Tetraploids had larger floral displays and different floral scent bouquets than diploids, but cytotypes differed only slightly in floral colour. Significant floral isolation was found between the two cytotypes. Flowering phenology of the two cytotypes greatly overlapped, and herbivory did not differ between cytotypes or was lower in tetraploids. In addition, tetraploids had higher reproductive success compared with diploids.Conclusions The results suggest that floral isolation and increased reproductive success of polyploids may help to explain their successful persistence in mixed-ploidy populations. These factors might even initiate transformation of populations from pure diploid to pure tetraploid.     

Ancient fig wasps indicate at least 34 Myr of stasis in their mutualism with fig trees

Fig wasps and fig trees are mutually dependent, with each of the 800 or so species of fig trees (Ficus, Moraceae) typically pollinated by a single species of fig wasp (Hymenoptera: Agaonidae). Molecular evidence suggests that the relationship existed over 65 Ma, during the Cretaceous. Here, we record the discovery of the oldest known fossil fig wasps, from England, dated at 34 Ma. They possess pollen pockets that contain fossil Ficus pollen. The length of their ovipositors indicates that their host trees had a dioecious breeding system. Confocal microscopy and scanning electron microscopy reveal that the fossil female fig wasps, and more recent species from Miocene Dominican amber, display the same suite of anatomical characters associated with fig entry and pollen-carrying as modern species. The pollen is also typical of modern Ficus. No innovations in the relationship are discernible for the last tens of millions of years.     

Do pollinators simultaneously select for inflorescence size and amount of floral scents? An experimental assessment on Escallonia myrtoidea

Abstract Correlation among phenotypic traits may be explained by correlational selection, the simultaneous selection of more than one trait, or by genetic and/or developmental factors. In Escallonia myrtoidea, a tree with scented flowers from central Chile, inflorescence size and the amount of floral scents were positively correlated. Independent manipulation of scent and inflorescence size in a factorial design was used to assess the occurrence of pollinator‐mediated correlational selection. Dependency on pollinators for seed set was also assessed. If pollinator‐mediated correlational selection occurs, nonadditive effects of both traits are expected, albeit only when the effect of manipulating the state of such traits is disadvantageous with respect to the naturally occurring inflorescences, and provided that plants are not limited by pollinators for seed set and pollen export. Escallonia myrtoidea was very strongly pollinator‐limited for seed set and pollen export. Pollinator‐mediated additive effects were not observed in the frequency of visits by pollinators, pollen export, and seed set of E. myrtoidea after experiencing scent and inflorescence size manipulations. Consequently, there was no support for pollinator‐mediated correlational selection between those traits, suggesting the prevalence of genetic and/or developmental factors.     

Sex-linked transcriptional divergence in the hermaphrodite fungus Neurospora tetrasperma

In the filamentous ascomycete Neurospora tetrasperma, a large (approx. 7 Mbp) region of suppressed recombination surrounds the mating-type (mat) locus. While the remainder of the genome is largely homoallelic, this region of recombinational suppression, extending over 1500 genes, is associated with sequence divergence. Here, we used microarrays to examine how the molecular phenotype of gene expression level is linked to this divergent region, and thus to the mating type. Culturing N. tetrasperma on agar media that induce sexual/female or vegetative/male tissue, we found 196 genes significantly differentially expressed between mat A and mat a mating types. Our data show that the genes exhibiting mat-linked expression are enriched in the region genetically linked to mating type, and sequence and expression divergence are positively correlated. Our results indicate that the phenotype of mat A strains is optimized for traits promoting sexual/female development and the phenotype of mat a strains for vegetative/male development. This discovery of differentially expressed genes associated with mating type provides a link between genotypic and phenotypic divergence in this taxon and illustrates a fungal analogue to sexual dimorphism found among animals and plants.     

Speciation genes in the genus Petunia

A major innovation in angiosperms is the recruitment of animal pollinators as a means to enhance the efficiency and specificity of pollen transfer. The implementation of this reproductive strategy involved the rapid and presumably coordinated evolution of multiple floral traits. A major question concerns the molecular identity of the genetic polymorphisms that specify the phenotypic differences between distinct pollination syndromes. Here, we report on our work with Petunia, an attractive model system for quantitative plant genetics and genomics. From interspecific crosses, we obtained F2 plants that differed in the length of the floral tube or the size of the limb. We used these plants to study the behaviour of the hawkmoth pollinator, Manduca sexta. Plants with larger limbs were preferentially visited, consistent with the notion that flower size affects visibility under low light conditions. The moths also displayed an innate preference for shorter tubes. However, in those cases that flowers with long tubes were chosen, the animals fed for equal time. Thus, the perception of tube length may help the moths, early on, to avoid those plants that are more difficult to handle.     

Insect Choice and Floral Size Dimorphism: Sexual Selection or Natural Selection?

In considerations of sexual floral size dimorphism, there is a conflict between sexual selection theory, which predicts that larger floral displays attract more pollinators, and optimality theory—particularly the ideal free distribution—which predict that pollinators' visits should match nutritional rewards. As an alternate explanation of this dimorphism, Müller reported that pollinators tend to visit larger male flowers before visiting smaller female flowers, thereby promoting effective pollination. To investigate optimality predictions, I offered pollinators a choice between smaller, less numerous, but more rewarding flowers; and larger, more numerous, but less rewarding flowers. Foragers initially favored the larger and more numerous flowers, but rapidly shifted preferences to conform with the predictions of the ideal free distribution. To test Müller's hypothesis, I offered pollinators choices between larger and smaller corollas of equal caloric reward. Results showed that although pollinators tended to visit larger corollas first, they did not visit them more often. These experiments highlight the need for further investigation into the tradeoff between natural and sexual selection, and their respective influences in pollination ecology.     

The contribution of a pollinating seed predator to selection on Silene latifolia females

Interactions, antagonistic or mutualistic, can exert selection on plant traits. We explored the role of Hadena bicruris, a pollinating seed predator, as a selective agent on its host, the dioecious plant Silene latifolia. We exposed females from artificial-selection lines (many, small flowers (SF) vs. few, large flowers (LF)) to this moth. Infestation did not differ significantly between lines, but the odds of attacked fruits aborting were higher in SF females. We partitioned selection between that caused by moth attack and that resulting from all other factors. In both lines, selection via moth attack for fewer, smaller flowers contrasted with selection via other factors for more flowers. In LF females, selection via the two components was strongest and selection via moth attack also favoured increased fruit abortion. This suggests that the moths act as more of a selective force on flower size and number via their predating than their pollinating role.