Spatial and temporal flower presentation in Apiaceae-Apioideae

Alle Doldengewächse (Apiaceae), darunter die größte, weltweit verbreitete Unterfamilie der Apioideen, weisen in ihren Blütenständen sehr einheitliche Merkmale auf. Die ‚Doppeldolden´ werden aus kleinen, weißen oder gelben Blüten gebildet und von vielen unspezialisierten Insekten besucht. Der uniforme Eindruck, der damit erweckt wird, ist unter Umständen ein Grund, dass die zugrundeliegende Morphologie bislang wenig untersucht wurde. Gegenstand der vorliegenden Dissertation ist es daher, die ‚verborgene Diversität´ im Blütenstandsbereich der Apiaceae -Apioideen mit dem Ziel darzustellen, den Einfluss der Architektur der Pflanzen auf die Art der Blütenpräsentation in Raum und Zeit und damit auf das Reproduktionssystem der Art zu ermitteln. Im ersten Kapitel zeigt der Vergleich von neun ausgewählten Arten, dass in den selbstfertilen und unspezifisch bestäubten Pflanzen durch Synchronisation und Rhythmik in der Präsentation von Blüten Fremdbefruchtung gefördert wird. Entweder durchlaufen die Pflanzen dabei nur eine getrennte männliche und weibliche Blühphase (Xanthoselinum alsaticum) oder der moduläre Bau der Pflanzen führt zu einer Folge männlicher und weiblicher Blühphasen (multizyklische Dichogamie). Die Diözie in Trinia glauca kann in diesem Zusammenhang als eine Trennung der Blühphasen auf verschiedengeschlechtliche Individuen gesehen werden. Für die andromonözischen Arten wird gezeigt, dass der Anteil funktional männlicher Blüten mit steigender Doldenordnung nicht einheitlich zu- oder abnimmt. Dadurch fungieren die Pflanzen zu verschiedenen Zeiten und mit unterschiedlicher Stärke eher als Pollenrezeptoren oder Pollendonatoren. Es wird deutlich, dass das ‚uniforme Muster‘ der Apioideen mit Dolden verschiedener Ordnungen, dichogamen Blüten und deren diversen Geschlechtsausbildungen ein komplexes Raum-Zeit-Gefüge zur Optimierung des Reproduktionssystems darstellt. Das zweite Kapitel stellt die Ergebnisse von Manipulationsexperimenten (Handbestäubung, Bestäuberabschirmung, Entfernen von Dolden niedriger Ordnung) an Chaerophyllum bulbosum dar, die zeigen, dass das Raum-Zeit-Gefüge in der Präsentation der Blüten der Art erlaubt, flexibel auf Umwelteinflüsse zu reagieren. Es stellt sich heraus, dass mechanische Beschädigungen kaum Einfluss auf den Andromonöziegrad und prozentualen Fruchtansatz der Individuen nehmen. Grundvoraussetzung der Reaktionsfähigkeit ist wiederum deren modulärer Bau. Dieser erlaubt es den Pflanzen, zusammen mit dem andromonöziebedingten Reservoir an - geschlechtlich flexiblen - männlichen Blüten, in den später angelegten Dolden fehlenden Fruchtansatz der Blüten früh blühender Dolden zu kompensieren. Im dritten Kapitel wird eine vergleichende Merkmalsanalyse an 255 Apioideen-Arten vorgelegt, die alle Verwandtschaftskreise, Wuchsformen und Verbreitungsgebiete der Gruppe repräsentieren. Ziel der Analyse war die Identifizierung von Merkmalssyndromen, die den Zusammenhang zwischen Architektur und Reproduktionssystem verdeutlichen sollten. Interessanterweise sind die einzigen Merkmale, die miteinander einhergehen, Protogynie und die graduelle Abnahme männlicher Blüten mit steigender Doldenordnung. Alle anderen Merkmale variieren unabhängig voneinander und erzeugen auf vielen verschiedenen Wegen immer wieder das gleiche Funktionsmuster, das als ‚breeding syndrome‘ der Apioideae gedeutet werden kann. Die Arbeit leistet einen wichtigen Beitrag zum Verständnis der Blütenstände der Apiaceen und darüber hinaus zu morphologischer Variation in ‚unspezialisierten‘ Reproduktionssystemen. Offensichtlich liegt in den Apioideen der Selektionsdruck auf der Aufrechterhaltung der generalisistischen Bestäubung und überprägt alle morphologisch-phylogenetischen Merkmalsvarianten.

The importance of visual and olfactory stimuli during flower visits in Apis mellifera

Flowers attract honeybees using colour and scent signals. Bimodality (having both scent and colour) in flowers leads to increased visitation rates, but how the signals influence each other in a foraging situation is still quite controversial. We studied four basic questions: When faced with conflicting scent and colour information, will bees choose by scent and ignore the “wrong” colour, or vice versa? To get to the bottom of this question, we trained bees on scent-colour combination AX (rewarded) versus BY (unrewarded) and tested them on AY (previously rewarded colour and unrewarded scent) versus BX (previously rewarded scent and unrewarded colour). It turned out that the result depends on stimulus quality: if the colours are very similar (unsaturated blue and blue-green), bees choose by scent. If they are very different (saturated blue and yellow), bees choose by colour. We used the same scents, lavender and rosemary, in both cases. Our second question was: Are individual bees hardwired to use colour and ignore scent (or vice versa), or can this behaviour be modified, depending on which cue is more readily available in the current foraging context? To study this question, we picked colour-preferring bees and gave them extra training on scent-only stimuli. Afterwards, we tested if their preference had changed, and if they still remembered the scent stimulus they had originally used as their main cue. We came to the conclusion that a colour preference can be reversed through scent-only training. We also gave scent-preferring bees extra training on colour-only stimuli, and tested for a change in their preference. The number of animals tested was too small for statistical tests (n = 4), but a common tendency suggested that colour-only training leads to a preference for colour. A preference to forage by a certain sensory modality therefore appears to be not fixed but flexible, and adapted to the bee’s surroundings. Our third question was: Do bees learn bimodal stimuli as the sum of their parts (elemental learning), or as a new stimulus which is different from the sum of the components’ parts (configural learning)? We trained bees on bimodal stimuli, then tested them on the colour components only, and the scent components only. We performed this experiment with a similar colour set (unsaturated blue and blue-green, as above), and a very different colour set (saturated blue and yellow), but used lavender and rosemary for scent stimuli in both cases. Our experiment yielded unexpected results: with the different colours, the results were best explained by elemental learning, but with the similar colour set, bees exhibited configural learning. Still, their memory of the bimodal compound was excellent. Finally, we looked at reverse-learning. We reverse-trained bees with bimodal stimuli to find out whether bimodality leads to better reverse-learning compared to monomodal stimuli. We trained bees on AX (rewarded) versus BY (unrewarded), then on AX (unrewarded) versus BY (rewarded), and finally on AX (rewarded) and BY (unrewarded) again. We performed this experiment with both colour sets, always using the same two scents (lavender and rosemary). It turned out that bimodality does not help bees “see the pattern” and anticipate the switch. Generally, bees trained on the different colour set performed better than bees trained on the similar colour set, indicating that stimulus salience influences reverse-learning.

A novel allele of FILAMENTOUS FLOWER reveals new insights on the link between inflorescence and floral meristem organization and flower morphogenesis

Background The Arabidopsis FILAMENTOUS FLOWER (FIL) gene encodes a YABBY (YAB) family putative transcription factor that has been implicated in specifying abaxial cell identities and thus regulating organ polarity of lateral organs. In contrast to double mutants of fil and other YAB genes, fil single mutants display mainly floral and inflorescence morphological defects that do not reflect merely a loss of abaxial identity. Recently, FIL and other YABs have been shown to regulate meristem organization in a non-cell-autonomous manner. In a screen for new mutations affecting floral organ morphology and development, we have identified a novel allele of FIL, fil-9 and characterized its floral and meristem phenotypes. Results The fil-9 mutation results in highly variable disruptions in floral organ numbers and size, partial homeotic transformations, and in defective inflorescence organization. Examination of meristems indicates that both fil-9 inflorescence and floral meristems are enlarged as a result of an increase in cell number, and deformed. Furthermore, primordia emergence from these meristems is disrupted such that several primordia arise simultaneously instead of sequentially. Many of the organs produced by the inflorescence meristems are filamentous, yet they are not considered by the plant as flowers. The severity of both floral organs and meristem phenotypes is increased acropetally and in higher growth temperature. Conclusions Detailed analysis following the development of fil-9 inflorescence and flowers throughout flower development enabled the drawing of a causal link between multiple traits of fil-9 phenotypes. The study reinforces the suggested role of FIL in meristem organization. The loss of spatial and temporal organization of fil-9 inflorescence and floral meristems presumably leads to disrupted cell allocation to developing floral organs and to a blurring of organ whorl boundaries. This disruption is reflected in morphological and organ identity aberrations of fil-9 floral organs and in the production of filamentous organs that are not perceived as flowers. Here, we show the role of FIL in reproductive meristem development and emphasize the potential of using fil mutants to study mersitem organization and the related effects on flower morphogenesis.

Pollinator responses to variation in floral display and flower size in dioecious Sagittaria latifolia (Alismataceae)

In animal-pollinated plants with unisexual flowers, sexual dimorphism in floral traits may be the consequence of pollinator-mediated selection. Experimental investigations of the effects of variation in flower size and floral display on pollinator visitation can provide insights into the evolution of floral dimorphism in dioecious plants. Here, we investigated pollinator responses to experimental arrays of dioecious Sagittaria latifolia in which we manipulated floral display and flower size. We also examined whether there were changes in pollinator visitation with increasing dimorphism in flower size. In S. latifolia, males have larger flowers and smaller floral displays than females. Visitation by pollinators, mainly flies and bees, was more frequent for male than for female inflorescences and increased with increasing flower size, regardless of sex. The number of insect visits per flower decreased with increasing floral display in males but remained constant in females. Greater sexual dimorphism in flower size increased visits to male inflorescences but had no influence on the number of visits to female inflorescences. These results suggest that larger flower sizes would be advantageous to both females and males, and no evidence was found that females suffer from increased flower-size dimorphism. Small daily floral displays may benefit males by allowing extended flowering periods and greater opportunities for effective pollen dispersal.

Support for the predictions of the pollinator-mediated stabilizing selection hypothesis

Aims Floral traits are frequency used in traditional plant systematics because Of their assumed constancy. One potential reason for the apparent constancy of flower size is that effective pollen transfer between flowers depends oil the accuracy of the physical fit between the flower and pollinator. Therefore, dowels are likely to he under stronger stabilizing selection for uniform size than vegetative plant parts. Moreover, as predicted by the pollinator-mediated stabilizing selection (PMSS) hypothesis, all accurate fit between flowers and their pollinators is likely to he more important for specialized pollination systems as found in many species with bilaterally symmetric (zygomorphic) flowers than for species, with radially symmetric (actinomorphic) flowers. Methods In a comparative study of 15 zygomorphic and 13 actinomorphic species ill Switzerland, we tested whether variation in flower size, among and within individuals, is smaller than variation ill leaf size and whether variation in flower size is smaller ill zygomorphic compared to actinomorphic species. Important findings Indeed, variation ill leaf length was significantly larger than variation in flower length and width. Within-individual variation ill flower and leaf sizes did not differ significantly between zygomorphic and actinomorphic species. In line with the predictions of the PMSS, among-individual variation ill flower length and flower width was significantly smaller for zygomorphic species than for actinomorphic species, while the two groups did not differ in leaf length variation. This suggests that plants with zygomorphic flowers have undergone stronger selection for uniform flowers than plants with actinomorphic flowers. This supports that the uniformity of flowers compared to vegetative structures within species, as already observed in traditional plant systematics, is, at least in part, a consequence of the requirement for effective pollination.

Paying with karma in the Buddha’s Flower Shop: Spiritual Economics in Early Indian Buddhism

Shen Weirong